Endocrine Disorders and Laminitis E

152 EQUINE VETERINARY EDUCATION / AE / MARCH 2013

Review Article Endocrine disorders and laminitis E. M. Tadros† and N. Frank*‡§ †Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, Tennessee, USA; ‡Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, Massachusetts, USA; and §Division of Medicine, School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, UK. *Corresponding author email: [email protected]

Keywords: horse; endocrinopathic laminitis; Cushing’s; equine metabolic syndrome; pars intermedia; insulin resistance

Summary Neuronal degeneration appears to result from age-related Two common endocrine disorders, pituitary pars intermedia oxidative stress (McFarlane 2007; McFarlane and Holbrook dysfunction and equine metabolic syndrome, predispose 2008), but other systemic conditions such as obesity may also horses and ponies to laminitis and may even induce the play a role. Obesity in human is associated with increased condition. The exact mechanisms involved in endocrinopathic oxidative stress due to the production of inflammatory laminitis have not been elucidated but hyperinsulinaemia and mediators (Fernandez-Sanchez et al. 2011), although one insulin resistance are currently being investigated. Obesity and study evaluating oxidative stress markers in obese ponies regional adiposity may also contribute to laminitis produced equivocal results (Treiber et al. 2009). Clinical signs susceptibility through the release of inflammatory cytokines of PPID are attributable to higher circulating concentrations of and adipokines. In the case of pituitary pars intermedia POMC-derived hormones as well as the space-occupying dysfunction, glucocorticoid excess is likely to weaken hoof effects of adenomas on surrounding tissues in advanced structures, alter vascular dynamics within the foot and induce cases. Classical signs include delayed shedding of the winter or exacerbate insulin resistance. This review will summarise haircoat, hypertrichosis (commonly referred to as hirsutism), current theories regarding the pathophysiology of skeletal muscle atrophy, polyuria and polydipsia. Pituitary pars endocrinopathic laminitis and provide recommendations for intermedia dysfunction is associated with laminitis (Johnson the diagnosis and management of these common equine et al. 2002; Donaldson et al. 2004), but a direct cause and endocrine disorders. effect relationship has not been established. Equine metabolic syndrome is both an endocrine and metabolic disorder and is described in greater detail Introduction in a consensus statement released by the American The 2 endocrine disorders that we will discuss in this review are College of Veterinary Internal Medicine (Frank et al. 2010c). pituitary pars intermedia dysfunction (PPID), also known as Key components of EMS include enhanced metabolic equine Cushing’s disease, and equine metabolic syndrome efficiency, increased adiposity, insulin resistance (IR) and (EMS). Alternative names for EMS include insulin resistance hyperinsulinaemia. Most importantly, affected horses and syndrome, peripheral Cushing’s syndrome and prelaminitic ponies are predisposed to pasture-associated laminitis (Treiber metabolic syndrome. Pituitary pars intermedia dysfunction et al. 2006). This syndrome is more common in ponies, Morgan is an endocrine disorder of older horses and ponies and horses, Paso Finos, Arabians and Warmbloods and is likely to be has been reviewed in greater detail by McFarlane (2011). a heritable trait (Treiber et al. 2006). Genetically predisposed Most affected animals are more than 15 years of age when horses often express the phenotype after overfeeding so both clinical signs of PPID are first noted and the risk of disease inherent and environmental factors play a role in the increases with age (Table 1). Horses with PPID suffer from development of EMS (Bailey et al. 2008; Carter et al. 2009b). hyperplasia or neoplasia of the pars intermedia, whereas Excess grain feeding or grazing on large pastures induce pituitary-dependent hyperadrenocorticism in other species obesity, which is a component of EMS in most cases. Regional such as the dog usually develops in the pars distalis. adiposity also develops as adipose tissues expand within the Corticotrophs of the pars distalis and melanotrophs of the pars neck region and other sites throughout the body. Enlargement intermedia secrete hormones derived from the prohormone of the neck crest is a physical characteristic that has pro-opiomelanocortin (POMC). While adrenocorticotropin been used as a phenotypic marker for EMS because neck hormone (ACTH), beta-endorphin and beta-lipotropin are the circumference and neck crest scores are negatively correlated primary products of POMC processing in the pars distalis, with insulin sensitivity in horses and ponies (Frank et al. 2006; melanotrophs of the pars intermedia further process ACTH and Carter et al. 2009a). Fat pads can also develop near the release alpha melanocyte stimulating hormone (a MSH) and tailhead or within the prepuce or mammary gland regions. corticotropin-like intermediate peptide (CLIP). Mammalian Many horses with EMS develop laminitis after being turned out pars intermedia melanotrophs are under tonic inhibition by on a new pasture or following rapid growth of grass in the spring dopaminergic periventricular neurons (Saland 2001) and or late summer, and obesity, regional adiposity and IR are all loss of dopaminergic inhibition results in pars intermedia established risk factors for pasture-associated laminitis in ponies hyperplasia. (Treiber et al. 2006; Carter et al. 2009c).

TABLE 1: Clinical presentation of pituitary pars intermedia dysfunction and equine metabolic syndrome

Pituitary pars intermedia dysfunction Equine metabolic syndrome

Pathophysiology Pathophysiology Loss of dopaminergic inhibition leads to hyperplasia or neoplasia Genetic predisposition (suspected) to obesity and insulin of the pituitary pars intermedia resistance Clinical presentation Clinical presentation Typically older than 15 years Typically 5–15 years of age when detected Hypertrichosis (hirsutism) or delayed shedding of haircoat; long Obesity and regional adiposity; prominent fat pads along the hairs may be retained year round on palmar and plantar crest of the neck, above the tail head or in the sheath/ aspect of limbs, behind elbows, or under mandibles; coat may mammary region; animals often described by owners as ‘easy appear dull keepers’ Hyperhidrosis, especially over neck and shoulders Occasional animals may be lean with abnormal fat deposition Polyuria and polydipsia Infertility or abnormal cyclicity in mares Weight loss or skeletal muscle atrophy; some animals may Chronic laminitis; acute episodes may occur after exposure to develop a sway-backed or pot-bellied appearance pasture that is high in nonstructural carbohydrate content Abnormal deposition of fat along the crest of the neck, above Insulin resistance is a consistent finding; dynamic endocrine the tail head, or in the sheath/mammary region testing may be necessary to detect insulin resistance if resting Recurrent or chronic infections such as sinusitis, skin infection, samples are inconclusive dental disease, or hoof abscesses Therapeutic goals Reproductive abnormalities including infertility and persistent Improvement in insulin sensitivity through weight loss, exercise lactation and a reduction in dietary carbohydrate consumption; Chronic laminitis, often insidious in onset pharmacological intervention in some cases Therapeutic goals Appropriate farrier care to manage chronic laminitis Improvement in clinical signs and endocrine abnormalities through pharmacological intervention Provision of supportive care including body clipping, appropriate farrier care, dentistry and nutrition

Insulin resistance and hyperinsulinaemia are components concurrently affected by EMS and PPID and may be at higher of EMS. Hyperinsulinaemia accompanies IR in most animals risk of developing laminitis. Insulin resistance associated with and is used as a diagnostic marker for this problem (Treiber EMS likely persists after PPID develops and may be et al. 2005). The degree of IR can vary in an individual animal exacerbated by glucocorticoid excess. over time due to factors such as dietary changes (Hoffman et al. 2003), fluctuations in body condition and fitness Potential pathophysiological mechanisms of (Freestone et al. 1992; Carter et al. 2009b), the production of endocrinopathic laminitis stress hormones (Geor et al. 2000; Tiley et al. 2007) and by season (Bailey et al. 2008; Frank et al. 2010a). Insulin resistance Hyperadrenocorticism is defined as failure of tissues to respond appropriately to insulin When PPID develops, melanotrophs of the pars intermedia (Kahn 1978). There are several reasons why tissues become secrete more POMC-derived hormones, including aMSH, insulin resistant, including a reduction in the density of insulin CLIP and ACTH. Higher ACTH concentrations are detected receptors on cell surfaces, malfunction of insulin receptors, in affected animals and this hormone stimulates defective internal signalling pathways and interference with cortisol secretion from the adrenal glands. A state of the synthesis or function of glucose transporter 4 proteins hyperadrenocorticism is induced, although serum cortisol (GLUT4). Although the exact mechanism of IR in EMS remains concentrations sometimes fall within reference range in horses to be fully elucidated, altered GLUT4 protein trafficking has with PPID and gross adrenal hyperplasia is an uncommon recently been demonstrated in adipose tissue and skeletal finding (Schott 2002; Miller et al. 2008). It is therefore assumed muscle from insulin-resistant horses (Waller et al. 2011a,b). that hyperadrenocorticism results from loss of circadian rhythm It is also important to consider the concept of converging and increased daily cumulative cortisol concentrations endocrinopathies in middle aged horses (10–20 years of age). (Dybdal et al. 1994; Haritou et al. 2008). Cortisol concentrations The authors hypothesise that ponies and horses with EMS are can also be lower than expected in horses with high ACTH predisposed to PPID because low grade inflammation and concentrations, suggesting that ACTH has lower biological oxidative stress associated with obesity contributes to activity in some PPID horses. neuronal degeneration and loss of dopaminergic inhibition. Histological alterations in the integument associated with Animals with EMS should therefore be closely monitored for hyperadrenocorticism in other species include protein PPID as they enter middle age and clinical signs of both depletion, inhibition of fibroblast growth and reduced endocrinopathies are detected in some cases. One important collagen synthesis (Johnson et al. 2002; Kahan et al. 2009). indication that this is occurring comes from the history with Johnson et al. (2002) described lengthening and attenuation owners often reporting that their obese middle-aged horse, of primary and secondary dermal lamellae in horses with with a history of EMS, has undergone a shift in metabolism and glucocorticoid excess and suggested that this represents begun to lose condition. The same horse might have retained pulling apart of lamellae as structures weaken. Vascular its winter haircoat for a few weeks longer or seemed to have changes may also accompany hyperadrenocorticism. aged rapidly in the last few months. These animals are Flow-mediated vasodilation of the brachial artery is reduced in

human with Cushing’s disease (Baykan et al. 2007) and Insulin Insulin hypertrophic remodelling of small resistance arteries occurs SENSITIVE RESISTANT within subcutaneous tissues (Rizzoni et al. 2009). Hooves of horses with PPID may therefore be more susceptible to lamellar ENDOTHELIAL CELL ENDOTHELIAL CELL failure and less capable of repair after laminitis has occurred. PI3K pathway MAPK pathway These assumptions are based on theory rather than scientific [Phosphatidylinositol-3 kinase] [Mitogen-activated protein kinase] evidence at this point and further studies are required to examine hooves from horses with PPID. Glucocorticoids inhibit the actions of insulin by disrupting post receptor signalling pathways (Buren et al. 2002; Ruzzin VASODILATION VASOCONSTRICTION et al. 2005) and administration of dexamethasone has been Nitric oxide Endothelin-1 shown to induce IR in horses (Tiley et al. 2007, 2008; Tóth et al. 2010). Interestingly, hyperinsulinaemia is detected in some horses with PPID (Reeves et al. 2001; Schott 2002), whereas others have normal insulin concentrations. One explanation for this observation is that IR only occurs with PPID when the horse is predisposed to this problem. An alternative explanation is that horses with PPID differ in the types and amounts of POMC-derived hormones secreted from the pars Fig 1: Theoretical relationships between insulin sensitivity and intermedia, so those with IR have higher ACTH-stimulated vascular tone in horses. Alterations in insulin sensitivity may cortisol secretion. It is important to assess insulin sensitivity in determine which pathway predominates after activation by circulating insulin. horses with PPID because affected animals respond differently to their diet and are predisposed to laminitis. In a recent study, horses with PPID had higher overall insulin enhances insulin sensitivity, so lower plasma concentrations concentrations across a 12 month period while grazing on are associated with IR (Kearns et al. 2006). Low adiponectin pasture when compared to unaffected aged horses (Frank concentrations are also associated with impaired et al. 2010b). Insulin concentrations above 188.6 mu/ml have endothelium-dependent vasodilation in obese humans also been identified as a poor prognostic indicator for 1–2 (Ritchie et al. 2004). Resistin is another adipokine that affects year survival in horses with PPID (McGowan et al. 2004). It insulin sensitivity. This hormone has been examined in mice and should also be noted that insulin concentrations can increase human and hyper-resistinaemia is associated with IR and type for other reasons, including systemic inflammation, stress and 2 diabetes mellitus (Radin et al. 2009). pain (Marik and Raghavan 2004; Frank 2009) and responses It should be noted that some insulin resistant horses exhibit may differ in horses with PPID. One final point is that some a leaner overall body condition. Abnormal fat deposition is horses with PPID suffer from laminitis whereas others do not. present regionally in some lean animals and may be The authors have observed that horses with PPID and responsible for the production of inflammatory mediators and concurrent IR are more likely to suffer from laminitis than adipokines that lower insulin sensitivity. Other horses appear those with normal insulin sensitivity, which suggests that IR is a normal and the mechanisms underlying IR in these animals key determinant or marker of laminitis susceptibility. require further study. Finally, laminitis may occur more readily in obese horses because they carry more weight on their hooves, which Obesity increases forces exerted upon dermo-epidermal attachments. Obesity, IR, hyperinsulinaemia and laminitis are associated in equids, but it should be noted that some obese animals exhibit Insulin resistance and vascular dynamics normal insulin sensitivity when tested (Treiber et al. 2006; Vick Insulin possesses vasoregulatory properties and this might et al. 2007; Carter et al. 2009c). These animals may be more explain why IR predisposes horses to laminitis. Slow vasodilation tolerant of obesity or require more time for IR to develop. One occurs in response to insulin through increased synthesis of theory linking obesity with IR is the release of inflammatory nitric oxide (NO) by endothelial cells (Muniyappa et al. 2007). cytokines from adipose tissues. More tumour necrosis factor However, insulin also promotes vasoconstriction by stimulating alpha (TNFa) is secreted from adipose tissues as body mass endothelin-1 (ET-1) synthesis and activating the sympathetic index increases in human and this inflammatory cytokine nervous system. Under normal conditions, the opposing inhibits insulin receptor signalling, which lowers insulin sensitivity actions of NO (vasodilation) and ET-1 (vasoconstriction) are in (Hartge et al. 2007). Vick et al. (2007) detected higher blood balance because both arms of the insulin signalling cascade TNFa mRNA expression in obese horses, which suggests that the are active; activation of the insulin receptor therefore same mechanism contributes to obesity-associated IR in stimulates 2 different signalling pathways within the vascular equids. Increased inflammatory cytokine production by endothelial cell (Fig 1). Nitric oxide is secreted when the adipose tissues may also contribute to laminitis susceptibility. phosphatidylinositol 3-kinase (PI3K) pathway is activated, Obesity also affects adipokine production by adipose whereas activation of the mitogen-activated protein kinase tissues. Adipokines are hormones produced by adipocytes (MAPK) pathway leads to release of ET-1 (Muniyappa et al. that have local (paracrine) and remote (endocrine) effects on 2008). Both the vasodilatory effects of insulin and tissues. Leptin and adiponectin are the most well known insulin-dependent stimulation of glucose uptake are mediated adipokines and obesity has been associated with elevated by PI3K and this pathway becomes disrupted when IR plasma leptin concentrations and lower plasma adiponectin develops. Consequently, vasoconstriction is promoted in concentrations in horses (Kearns et al. 2006). Adiponectin insulin resistant animals because only the MAPK pathway

remains fully functional. Development of compensatory hyperinsulinaemia in response to IR can further stimulate MAPK signalling and increase ET-1 synthesis (Kim et al. 2006). Eades et al. (2007) detected an increase in plasma ET-1 concentration within blood collected from digital veins 12 h after carbohydrate was administered to induce laminitis in healthy horses. This finding suggests that digital vessels undergo vasoconstriction as a result of carbohydrate overload in horses, which may contribute to the development of laminitis. Horses with chronic IR may be more likely to develop laminitis since vasoconstriction is already promoted.

Hyperinsulinaemia and vascular dynamics Laminitis has been experimentally-induced in healthy ponies and Standardbred horses by inducing hyperinsulinaemia (Asplin et al. 2007; de Laat et al. 2010). In both studies, glucose and insulin were infused i.v. according to the euglycaemic-hyperinsulinaemic clamp procedure, with mean Fig 2: Photograph of the right side of a horse with retained winter serum insulin concentrations exceeding 1000 mu/ml. Mean time hairs. Longer hairs that were lighter in colour were present in this to onset of Obel grade 2 laminitis was 46 h in horses and region. 55 h in ponies and hoof wall surface temperature increased in response to insulin infusion, indicating that vasodilation mandibles. These hairs can become lighter in colour over occurred within the foot. These results suggest that hyperinsulinaemia itself induces laminitis through a time as a result of exposure to sunlight (Fig 2). mechanism involving vasodilation. If this is the case, then hyperinsulinaemia-induced vasodilation would overcome Shift in metabolism vasoconstriction promoted by IR. It has also been proposed Owners sometimes report that their horse has undergone a that hyperinsulinaemia-induced vasodilation increases glucose shift in metabolism and is now losing weight and body delivery to hoof tissues, leading to local glucotoxicity (de Laat condition. This problem is difficult to confirm unless a et al . 2010). This may lead to the formation of advanced complete dietary history has been recorded but clinicians glycation end products that damage tissues. Advanced should suspect PPID when a middle-aged horse begins to glycation end products develop as glucose reacts with amino acids within tissues and these products play an important role in lose muscle mass and requires more calories than it did in the development of diabetic angiopathy in human (Yamagishi the past. 2009). Regional adiposity Clinical diagnosis and management of pituitary This clinical sign is associated with both EMS and PPID. In pars intermedia dysfunction the case of EMS, regional adiposity first develops at an earlier age and then persists. In contrast, detection of Presenting complaints regional adiposity for the first time in an older (>15 years) Classical clinical signs of PPID include hypertrichosis horse indicates the development of PPID. As discussed (commonly referred to as hirsutism) and affected horses are below, horses with EMS can develop PPID as they get older. relatively easy to identify once the condition has become advanced. Early disease, however, is more challenging to These patients have fat deposits that were previously recognise. Early signs of PPID include delayed shedding of associated with EMS and then become a component of the winter haircoat, a perceived shift in metabolism, regional PPID. adiposity, infertility and laminitis. Infertility Delayed shedding of the winter haircoat Pituitary pars intermedia dysfunction should be considered Affected horses exhibit delayed shedding of the winter if an aged mare develops fertility problems. More research haircoat, increased hair length (hypertrichosis) and is required to determine the effects of PPID on the dullness of the haircoat. If this problem is suspected, owners reproductive cycle and uterine environment. At present, should record the time that their horse sheds its winter only anecdotal evidence is available to suggest that haircoat and compare it with other horses in the same reproductive performance improves in mares with PPID barn. that receive treatment.

Diagnostic testing Retention of winter hairs in certain regions of the body Resting ACTH concentrations and the overnight Some horses with early PPID shed most of their winter dexamethasone suppression test (DST) are easily performed haircoat, but retain hairs along the palmar or plantar (Table 2), but the sensitivity of these tests must be questioned aspects of the legs, behind the elbow or beneath the for early PPID. In a study performed by Miller et al. (2008),

TABLE 2: Recommended diagnostic tests for pituitary pars intermedia dysfunction

PPID: Resting ACTH concentration PPID: Dexamethasone suppression test

Considerations Considerations • Higher concentrations are detected in healthy horses in the • False positives are detected in healthy horses in the late late summer and autumn summer and autumn • Pain and stress raise ACTH concentrations • Owner concerns about inducing laminitis Procedure Procedure • Collect blood in a tube containing EDTA • Collect a preinjection blood sample (optional) • Keep the blood sample cool at all times • Inject 0.04 mg/kg bwt (20 mg for a 500-kg horse) • Centrifuge the same morning or afternoon dexamethasone i.v. or i.m. • Mail to the laboratory with a cool pack • Collect a blood sample 19 or 24 h later Interpretation Interpretation • Positive if ACTH >35 pg/ml (>50 pg/ml in August to October) • Positive if cortisol concentration >10 ng/ml (27 nmol/l) at 19 • Results may fall within reference range for horses with early/ or 24 h mild PPID. • Results may be normal in horses with early/mild PPID • Use the fall as a natural stimulation test • Only the negative result is significant when testing in the late summer or autumn

resting ACTH concentrations were within reference range for inhibition of melanotrophs. Interaction of the drug with D2 5 of 5 horses with grade 3/5 pituitary pars intermedia lesions, receptors inhibits hormone secretion and may also slow the 6 of 12 horses with grade 4/5 lesions and 1 of 4 horses with progression of disease (Donaldson et al. 2002). Pergolide grade 5/5 lesions. In addition, measurement of plasma ACTH is prescribed on a total dose basis, using a starting dose during the late summer and early fall has been avoided of 1.0 mg/day for horses and larger ponies with PPID. A to minimise the likelihood of obtaining false-positive results due to seasonal increases in ACTH concentration (McFarlane lower starting dose of 0.002 mg/kg bwt (range of et al. 2004; Donaldson et al. 2005). However, recent studies 0.002–0.01 mg/kg bwt daily) can be calculated for small have suggested that differences in plasma ACTH ponies or miniature horses. Some owners report loss of concentrations between normal horses and those affected appetite when pergolide is first started. If anorexia by PPID may be most pronounced during this time (Frank develops, treatment should be halted for 2 days or until et al. 2010a), therefore establishing season-specific reference appetite improves and then restarted at 0.25 mg/day for 2 ranges to facilitate testing in the late summer and early fall days, 0.5 mg/day for 2 days and 0.75 mg/day for 2 days. could improve the sensitivity of this diagnostic procedure. The Another side effect of pergolide treatment is temporary DST had high specificity when examined by Beech et al. dullness after initiating therapy and this can be addressed (2007), but sensitivity ranged from 23–66% depending upon which groups were compared. Other tests for PPID are being using the same approach. Horses with advanced PPID developed, including the thyrotropin-releasing hormone receive higher dosages, with a maximum daily dosage of stimulation test (Beech et al. 2007) and oral domperidone 5 mg/day for horses with severe disease. Pergolide and challenge (Miller et al. 2008) and these tests warrant cyproheptadine can also be administered in combination. consideration. It must be recognised that the goals of medical treatment A complicating factor in the development of antemortem vary with disease severity; the dosage selected for horses diagnostic tests is the lack of a reliable gold standard for with early PPID should be adjusted until normal diagnostic identifying PPID. Results have been compared to post mortem test results are obtained, whereas treatment is palliative in histological evaluation of the pituitary; however, there is little consensus among pathologists on the histological criteria that horses with advanced disease. It is only reasonable to define PPID and therefore only moderate agreement expect medical treatment to ameliorate disease in these between antemortem and post mortem diagnosis (McFarlane advanced cases of PPID. et al. 2005). Pituitary lesions have also been identified in clinically normal animals (van der Kolk et al. 2004) and overlap between normal ageing changes and early disease further Cyproheptadine complicates diagnosis. It should also be noted that all Both pergolide and cyproheptadine lower plasma ACTH available antemortem diagnostic tests are limited in their concentrations in horses with PPID (Perkins et al. 2002), but ability to detect early or mild disease so the clinician must pergolide is more effective (Donaldson et al. 2002). sometimes decide to institute treatment on the basis of clinical Donaldson et al. (2002) reported that 17 of 20 horses (85%) judgement alone. In these cases, pergolide can be with PPID improved with pergolide treatment, compared administered as a therapeutic trial. with only 2/7 horses treated with cyproheptadine. Cyproheptadine antagonises serotonin, which is thought Management to be a stimulatory neurotransmitter for pars intermedia Pergolide mesylate melanotrophs. Treated horses occasionally exhibit This ergot alkaloid dopamine receptor agonist is sedation when treatment is initiated. A dosage of administered to horses with PPID to restore dopaminergic 0.25 mg/kg bwt per os q. 12 h is recommended.

Trilostane This drug is a 3-beta hydroxysteroid dehydrogenase inhibitor and acts by inhibiting corticosteroid synthesis within the adrenal cortex. Trilostane is commonly used in dogs for the management of pituitary-dependent hyperadrenocorticism when increased ACTH secretion from the pars distalis induces adrenal hyperplasia. However, the reported incidence of adrenal hyperplasia is low (20%) in horses with PPID (Schott 2002) so this may limit the usefulness of trilostane in this species. With this stated, McGowan and Neiger (2003) reported improved clinical signs in 20 horses with PPID treated with trilostane at a mean dosage of 0.5 mg/kg bwt. Lethargy resolved, polyuria/polydipsia decreased and recurrent or chronic laminitis improved in 13 of 16 affected horses. Combined dexamethasone/thyrotropin-releasing hormone test results improved after treatment but did not return to normal. The Fig 3: Photograph of the enlarged neck crest of a horse with Equine recommended dosage for trilostane has subsequently Metabolic Syndrome. been increased to 1.0 mg/kg bwt (q. 24 h; given in the evening) for horses with PPID. In general, EMS should be suspected in any obese horse with regional adiposity that the owner describes as an Combination therapy ‘easy keeper’ or ‘good doer’. Some horses with PPID respond to combination treatment with pergolide and cyproheptadine. One approach is to reach the maximum pergolide dosage of 5 mg/day and Obesity and regional adiposity then add cyproheptadine treatment (0.25 mg/kg bwt per Most horses with EMS are obese and show enlargement of et al os q.12 h) to the regimen. Other clinicians add adipose tissues within the neck crest (Frank . 2006; et al cyproheptadine when the pergolide dosage reaches Carter . 2009a), commonly referred to as a cresty neck Fig 3 3 mg/day (Schott 2006). ( ). Fat pads can also develop close to the tailhead and within the prepuce or mammary gland region and horses sometimes present with the complaint of preputial Dietary management of PPID swelling or mammary gland enlargement. Affected horses Since some horses with PPID are insulin-resistant and occasionally have randomly distributed subcutaneous others have normal insulin sensitivity, the diet of each adipose tissue deposits. If regional adiposity first develops in affected horse must be adjusted accordingly. an older horse (>15 years), it is more likely to be associated Insulin-resistant PPID horses are challenging to manage if with PPID. the animal is losing weight or being worked. In these cases caloric intake must be increased without exacerbating IR. A diet of hay and low-sugar/low-starch Laminitis pellets is recommended with one half to 1 cup vegetable Acute laminitis is the presenting complaint for many horses oil added twice daily to increase digestible energy with EMS. Laminitis appears to occur spontaneously intake. Pasture access should be controlled to avoid without any history of grain overload, bacterial disease or sudden changes in carbohydrate intake. In contrast, retained placenta. However, further questioning of the insulin-sensitive PPID horses can be fed as normal, with owner or examination of the surroundings may reveal that senior feeds, sweet feed or oats fed with hay to provide laminitis is associated with changes in the pasture grass, additional calories if needed. including rapid growth in the spring, drought in the summer, frost in the winter or transfer to a new pasture. Laminitis may also occur at a subclinical level and lead to structural Clinical diagnosis and management of equine changes within the hoof that manifest as divergent hoof metabolic syndrome rings or radiographic evidence of distal (third) phalanx Presenting complaints rotation. Age Equine metabolic syndrome first develops in the younger Infertility horse (<15 years of age) and it is likely that this condition Impaired reproductive performance may be a presenting has a genetic basis. Some horses become obese when complaint for EMS. Alterations in reproductive cycling have they reach maturity whereas others develop obesity later been detected in obese insulin-resistant mares (Vick et al. in life when they are overfed and inadequately exercised. 2006).

TABLE 3: Recommended diagnostic tests for insulin resistance

EMS: Resting insulin concentration EMS: Combined glucose insulin test

Considerations Considerations • Use as a screening test • Used to detect insulin resistance (IR) when the fasting insulin • Also measure the glucose concentration; persistent concentration is normal or when you want to quantify hyperglycaemia is a major concern insulin sensitivity • Risk of inducing clinical hypoglycaemia in insulin-sensitive horses • Administer 60–120 ml 50% dextrose and feed the horse if hypoglycaemia occurs Procedure Procedure • Ask the owner to leave only one flake of hay in the stall • Collect a preinjection blood sample after 22.00 h the night before and do not feed the horse • Infuse 150 mg/kg bwt glucose (50% dextrose) and then 0.10 until after samples are collected iu insulin i.v. • Collect blood in the morning • Collect blood samples at 1, 5, 15, 25, 35, 45, 60, 75, 90, 105, • Submit samples for glucose and insulin concentrations 120, 135 and 150 min (or until normal result) and measure glucose on a hand-held glucometer. • Measure insulin concentrations at 0 and 45 min Interpretation Interpretation • Hyperinsulinaemia if the insulin concentration exceeds • Insulin resistance is present if the blood glucose 20 mu/ml (mu/l) concentration is above the preinjection value for Ն45 min • Glucose concentrations are within reference range in most • An insulin concentration >100 mu/ml at 45 min indicates an cases (euglycaemia) excessive pancreatic response consistent with • Detection of persistent hyperglycaemia indicates type 2 compensated IR diabetes mellitus; insulin concentration may be normal or elevated

New tests in development Oral sugar test: Corn syrup (0.15 ml/kg bwt) is administered orally via dose syringe and a blood sample is drawn 60–90 min later. Higher blood glucose (>115 mg/dl [6.4 mmol/l]) and insulin (>60 mu/ml) concentrations are detected in insulin-resistant horses. Infeed oral glucose challenge test: Dextrose powder (1 g/kg bwt) is mixed with a nonglycaemic feed (e.g. chaff) and fed to the horse. A blood sample is collected 2 h later and an insulin concentration >85 mu/ml is supportive of IR.

Diagnostic testing with caution. Results that fall far outside the normal range Diagnostic testing for EMS currently focuses upon detection of are more likely to indicate a true positive. IR and hyperinsulinaemia. Tests vary in their complexity and a Glucose concentrations should be measured at compromise must be reached between accuracy and ease the same time. Most insulin-resistant horses maintain of testing. It must also be recognised that all of the available euglycaemia and hyperglycaemia is a significant concern. tests are affected by pain and stress, which accompanies Hyperglycaemia signals loss of glycaemic control, which is laminitis and testing should be delayed until the animal has stabilised. Unfortunately this prevents the clinician from seen in some patients with pancreatic insufficiency. Resting assessing the animal in its exacerbated state, which is when insulin concentrations may be high or within reference laminitis first developed. Results must be interpreted range in these patients and hyperglycaemia is the key accordingly as horses with mild IR at the time of testing may finding. This is referred to as type 2 diabetes mellitus if have been more severely affected when laminitis developed hyperglycaemia persists (Durham et al. 2009). several weeks beforehand.

Resting insulin concentration Dynamic testing This is a screening test for IR and easy to perform. Horses There are occasions when EMS is strongly suspected on the must undergo a short fast before samples are collected basis of the history and clinical findings, yet resting insulin and this is accomplished by leaving only one flake of hay concentrations fall within the reference range. In these with the animal after 22.00 h the night before and situations, a dynamic test should be performed to then collecting a blood sample the following morning. challenge the system. This can be accomplished by Reference ranges for insulin vary among laboratories performing an i.v. glucose tolerance test, administering according to the assay used and control population. With dextrose orally or feeding a test meal. For all of these tests, the radioimmunoassay used in our laboratory, a cut-off the horse or pony should be fasted by leaving only one value of 20 mu/ml defines hyperinsulinaemia (Table 3). flake of hay in the stall after 22.00 h the night before. A Because factors such as stress, duration of fasting and combined glucose-insulin test (CGIT) has been developed possibly diurnal variation can impact insulin sensitivity over for use in horses and can be used to assess insulin sensitivity short periods of time (Ralston 2002), single resting insulin in approximately 1 h (Eiler et al. 2005; Frank 2009). This test concentrations outside of reference range or small involves insertion of an i.v. catheter and administration of variations in serial measurements should be interpreted dextrose followed immediately by insulin. An oral sugar test

(OST) has also been introduced in the USA where corn Levothyroxine sodium syrup is readily available in supermarkets. Corn syrup is When administered at high dosages, levothyroxine induces administered orally after a short fast at a dosage of weight loss in horses and is accompanied by increased 0.15 ml/kg bwt (150 mg sugar/kg bwt) and a blood sample insulin sensitivity (Sommardahl et al. 2005; Frank et al. is drawn 60–90 min later. Higher blood glucose (>115 mg/dl 2008a,b). Pretreatment with levothyroxine for 14 days has [6.4 mmol/l]) and insulin (>60 mu/ml) concentrations are also been shown to prevent horses from developing IR detected in insulin-resistant horses. An in-feed oral glucose following endotoxin infusion (Tóth et al. 2010). Levothyroxine challenge test (OGT) can be performed as an alternative has been administered at an approximate dosage of by mixing dextrose powder at a dosage of 1 g/kg bwt with 0.1 mg/kg bwt, which is rounded to 48 mg/day for horses a nonglycaemic feed. A blood sample is collected 2 h weighing 450–525 kg. It is assumed that levothyroxine later and insulin concentrations >85 mu/ml are consistent induces weight loss by raising circulating thyroxine with IR. Although administration of sugar to insulin-resistant concentrations and stimulating basal metabolic rate. horses may be of concern to some owners, the authors are Weight loss is enhanced by restricting caloric intake and not aware of any cases in which testing procedures have increasing exercise at the same time that levothyroxine is induced laminitis. administered. Horses should not be permitted to graze on pasture because levothyroxine is likely to induce Management hyperphagia, which offsets the effects of treatment. Equine metabolic syndrome is a disorder that should be Levothyroxine is primarily administered for the purpose of managed with diet, housing and exercise changes, rather accelerating weight loss in obese horses and is prescribed than drugs in most cases. The 2 principal strategies for for 3–6 months while other management practices are addressing IR in horses are to 1) induce weight loss in obese instituted. This drug is reasonably priced in the United States horses and ponies and 2) improve insulin sensitivity through but is considerably more expensive in Europe. dietary management and exercise (Geor and Harris 2009). Obese horses should be placed on a weight reduction diet composed of hay plus a protein, vitamin and mineral Metformin hydrochloride supplement. Horses should initially receive hay in amounts Metformin has been used for decades in human medicine. equivalent to 1.5% of ideal bwt per day (i.e. 7.5 kg for a 500 kg This biguanide drug is administered to control horse). If the horse or pony does not begin to lose weight after hyperglycaemia and increase tissue insulin sensitivity in one month on this diet, the amount of hay fed should be lowered to 1.0% of ideal bwt (5 kg for a 500 kg horse). The human with diabetes mellitus. It suppresses hepatic weight reduction diet should be continued until an ideal body glucose production by activating AMP-activated protein condition score has been attained. Grain or pellets should be kinase (AMPK), which inhibits gluconeogenesis and completely eliminated from the diet and there should be no lipogenesis while increasing fatty acid oxidation and access to pasture during the weight loss period. Analysis of hay lipolysis (Kim et al. 2008). Two key gluconeogenesis is recommended to ensure that the nonstructural enzymes, phosphoenolpyruvate carboxykinase and carbohydrate (NSC) content of the forage is low. Hay with NSC glucose-6-phosphatase are inhibited by metformin content less than 10% on a dry matter basis is ideal for through this mechanism. The insulin-sensitising effects of insulin-resistant horses. Hay can be soaked for 1 h in cold water to reduce NSC content; however, this strategy does not reliably metformin may also be mediated by skeletal muscle reduce NSC content below 10% and may not be adequate AMPK, causing increased GLUT4 abundance within cell when managing an insulin-resistant animal (Longland et al. membranes and enhanced glucose uptake (Musi et al. 2009). Obese horses should also be exercised because 2002). One study also describes AMPK-independent effects exercise induces weight loss (Carter et al. 2010) and is likely to of metformin on cardiac muscle, with results indicating that lower appetite and improve insulin sensitivity. A horse with EMS p38 mitogen-activated protein kinase and protein kinase C should ideally be housed in a small paddock 0.25 to 0.5 acre so pathways are activated (Saeedi et al. 2008). that there is sufficient room for exercise. With the exception of Only a small number of studies have been performed severely affected animals with recurrent laminitis, horses with to explore the use of metformin in horses. Durham et al. EMS can be housed in grass paddocks, as long as a grazing muzzle is used to restrict grass consumption. One additional (2008) reported that resting insulin concentrations and benefit of grazing muzzles is that the horse or pony exercises proxy measures of insulin sensitivity improved in horses and more as it works harder to graze on grass. Interacting with a ponies with presumed insulin resistance when treated with companion horse in the same paddock also increases metformin at a dosage of 15 mg/kg bwt per os q. 12 h. exercise. Refer to the section on PPID for dietary management Administration of metformin at this dosage was associated of lean insulin-resistant horses. with positive clinical outcomes, but a subsequent study Veterinarians have a responsibility to recommend evaluating the same dose did not demonstrate improved management changes and discourage horse owners from insulin sensitivity or changes in indices of glucose and insulin administering drugs as a substitute. However, there are 2 indications for pharmacological intervention: 1) short-term dynamics in nonobese insulin-resistant ponies (Tinworth (3–6 months) treatment while management changes are et al. 2011). Hustace et al. (2009) reported that the oral taking effect and 2) refractory cases. Two drugs have been bioavailability of 3 g metformin was 7.1 Ϯ 1.5% in fasted examined to date. horses and 3.9 Ϯ 1.0% in fed animals and both trough and

predicted peak concentrations were lower in ponies Bailey, S.R., Habershon-Butcher, J.L., Ransom, K.J., Elliott, J. and receiving metformin at 15 mg/kg bwt per os q. 12 h for 21 Menzies-Gow, N.J. (2008) Hypertension and insulin resistance in a mixed-breed population of ponies predisposed to laminitis. Am. J. days than values associated with therapeutic efficacy in vet. Res. 69, 122-129. human (Tinworth et al. 2010). The current recommendation Baykan, M., Erem, C., Gedikli, O., Hacihasanoglu, A., Erdogan, T., Kocak, for metformin is, therefore, 30 mg/kg bwt per os q. 8–12 h. M., Durmus, I., Korkmaz, L. and Celik, S. (2007) Impairment of flow-mediated vasodilatation of brachial artery in patients with Cushing’s Syndrome. Endocrine 31, 300-304. Response to treatment Beech, J., Boston, R., Lindborg, S. and Russell, G.E. (2007) Weight loss can be monitored using a weight tape or Adrenocorticotropin concentration following administration of walk-on scale and neck circumference measurements thyrotropin-releasing hormone in healthy horses and those with pituitary pars intermedia dysfunction and pituitary gland may be useful for assessing improvement in regional hyperplasia. J. Am. vet. med. Ass. 231, 417-426. adiposity. Fasting blood glucose and insulin concentrations Buren, J., Liu, H.X., Jensen, J. and Eriksson, J.W. (2002) Dexamethasone and dynamic test results should return to normal with impairs insulin signalling and glucose transport by depletion of insulin treatment. However, there are some patients that remain receptor substrate-1, phosphatidylinositol 3-kinase and protein kinase B in primary cultured rat adipocytes. Eur. J. Endocrinol. 146, insulin-resistant in the face of management changes and 419-429. medical treatments. These animals remain at higher risk for Carter, R.A., Geor, R.J., Burton Staniar, W., Cubitt, T.A. and Harris, P.A. laminitis and every effort should be made to avoid triggers (2009a) Apparent adiposity assessed by standardised scoring for this disease. Severely affected horses and ponies should systems and morphometric measurements in horses and ponies. Aust. vet. J. 179, 204-210. be held off pasture and housed in dry lots or small grass Carter, R.A., McCutcheon, L.J., George, L.A., Smith, T.L., Frank, N. and paddocks. Geor, R.J. (2009b) Effects of diet-induced weight gain on insulin Type 2 diabetes mellitus is a concern because sensitivity and plasma hormone and lipid concentrations in horses. Am. J. vet. Res. 70, 1250-1258. glucosuria causes electrolyte depletion and anorexia. Diabetic horses are also more susceptible to Carter, R.A., McCutcheon, L.J., Valle, E., Meilahn, E.N. and Geor, R.J. (2010) Effects of exercise training on adiposity, insulin sensitivity, and hypertriglyceridaemia when lipids are mobilised in response plasma hormone and lipid concentrations in overweight or obese, to stress and negative energy balance. Horses with insulin-resistant horses. Am. J. vet. Res. 71, 314-321. diabetes mellitus that are in good general heath should be Carter, R.A., Treiber, K.H., Geor, R.J., Douglass, L. and Harris, P.A. (2009c) Prediction of incipient pasture-associated laminitis from managed with dietary changes and administration of hyperinsulinaemia, hyperleptinaemia and generalised and metformin, whereas patients in crisis require exogenous localised obesity in a cohort of ponies. Equine vet. J. 41, 171-178. insulin. Short-acting regular (soluble) insulin can be de Laat, M.A., McGowan, C.M., Sillence, M.N. and Pollitt, C.C. (2010) administered i.v. via constant rate infusion or long-acting Equine laminitis: induced by 48 h hyperinsulinaemia in Standardbred horses. Equine vet. J. 42, 129-135. insulin can be given by subcutaneous injection. The Donaldson, M.T., Jorgensen, A.J. and Beech, J. (2004) Evaluation of decision to administer insulin is based upon the degree of suspected pituitary pars intermedia dysfunction in horses with glucosuria and hypertriglyceridaemia. Diabetes mellitus is laminitis. J. Am. vet. med. Ass. 224, 1123-1127. sometimes associated with PPID and pergolide should be Donaldson, M.T., LaMonte, B.H., Morresey, P., Smith, G. and Beech, J. administered to these patients. (2002) Treatment with pergolide or cyproheptadine of pituitary pars intermedia dysfunction (equine Cushing’s disease). J. vet. Intern. Med. 16, 742-746. Future directions Donaldson, M.T., McDonnell, S.M., Schanbacher, B.J., Lamb, S.V., McFarlane, D. and Beech, J. (2005) Variation in plasma The endocrine disorders discussed increase the risk of laminitis adrenocorticotropic hormone concentration and dexamethasone and diagnostic testing should be performed to detect these suppression test results with season, age, and sex in healthy ponies conditions. Body condition scoring should also be conducted and horses. J. vet. Intern. Med. 19, 217-222. as part of biannual wellness evaluations and owners must Durham, A.E., Rendle, D.I. and Newton, J.E. (2008) The effect of recognise that obesity threatens the health of their horse. It is metformin on measurements of insulin sensitivity and beta cell response in 18 horses and ponies with insulin resistance. Equine vet. relatively easy to diagnose endocrine disorders in advanced J. 40, 493-500. cases but greater emphasis should be placed upon identifying Durham, A.E., Hughes, K.J., Cottle, H.J., Rendle, D.I. and Boston, R.C. and treating endocrinopathies in their earlier stages. Research (2009) Type 2 diabetes mellitus with pancreatic b cell dysfunction in should focus upon the development of more sensitive 3 horses confirmed with minimal model analysis. Equine vet. J. 41, screening tests for EMS and PPID in horses, with the aim of 924-929. preventing laminitis. Dybdal, N.O., Hargreaves, K.M., Madigan, J.E., Gribble, D.H., Kennedy, P.C. and Stabenfeldt, G.H. (1994) Diagnostic testing for pituitary pars intermedia dysfunction in horses. J. Am. vet. med. Ass. 204, 627- Authors’ declaration of interests 632. Dr Frank is a consultant for Boehringer Ingelheim, manufacturer Eades, S.C., Stokes, A.M., Johnson, P.J., Leblanc, C.J., Ganjam, V.K., Buff, P.R. and Moore, R.M. (2007) Serial alterations in digital of pergolide. The trade name and product name are not hemodynamics and endothelin-1 immunoreactivity, mentioned. platelet-neutrophil aggregation, and concentrations of nitric oxide, insulin, and glucose in blood obtained from horses following carbohydrate overload. Am. J. vet. Res. 68, 87-94. References Eiler, H., Frank, N., Andrews, F.M., Oliver, J.W. and Fecteau, K.A. (2005) Asplin, K.E., Sillence, M.N., Pollitt, C.C. and McGowan, C.M. (2007) Physiologic assessment of blood glucose homeostasis via combined Induction of laminitis by prolonged hyperinsulinaemia in clinically intravenous glucose and insulin testing in horses. Am. J. vet. Res. 66, normal ponies. Aust. vet. J. 174, 530-535. 1598-1604.

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Rizzoni, D., Porteri, E., De Ciuceis, C., Rodella, L.F., Paiardi, S., Rizzardi, N., Tóth, F., Frank, N., Geor, R.J. and Boston, R.C. (2010) Effects of Platto, C., Boari, G.E., Pilu, A., Tiberio, G.A., Giulini, S.M., Favero, G., pretreatment with dexamethasone or levothyroxine sodium on Rezzani, R., Rosei, C.A., Bulgari, G., Avanzi, D. and Rosei, E. (2009) endotoxin-induced alterations in glucose and insulin dynamics in Hypertrophic remodeling of subcutaneous small resistance arteries horses. Am. J. vet. Res. 71, 60-68. in patients with Cushing’s syndrome. J. Clin. Endocrinol. Metab. 94, Treiber, K., Carter, R., Gay, L., Williams, C. and Geor, R. (2009) 5010-5018. Inflammatory and redox status of ponies with a history of Ruzzin, J., Wagman, A.S. and Jensen, J. (2005) Glucocorticoid-induced pasture-associated laminitis. Vet. Immunol. Immunopathol. 129, insulin resistance in skeletal muscles: defects in insulin signalling and 216-220. the effects of a selective glycogen synthase kinase-3 inhibitor. Treiber, K.H., Kronfeld, D.S., Hess, T.M., Boston, R.C. and Harris, P.A. (2005) Diabetologia 48, 2119-2130. Use of proxies and reference quintiles obtained from minimal model Saeedi, R., Parsons, H.L., Wambolt, R.B., Paulson, K., Sharma, V., analysis for determination of insulin sensitivity and pancreatic Dyck, J.R., Brownsey, R.W. and Allard, M.F. (2008) Metabolic beta-cell responsiveness in horses. Am. J. vet. Res. 66, 2114-2121. actions of metformin in the heart can occur by AMPK-independent Treiber, K.H., Kronfeld, D.S., Hess, T.M., Byrd, B.M., Splan, R.K. and Staniar, mechanisms. Am. J. Physiol. Heart Circ. Physiol. 294, H2497-H2506. W.B. (2006) Evaluation of genetic and metabolic predispositions and Saland, L.C. (2001) The mammalian pituitary intermediate lobe: an nutritional risk factors for pasture-associated laminitis in ponies. update on innervation and regulation. Brain Res. Bull. 54, 587-593. J. Am. vet. med. Ass. 228, 1538-1545. Schott, H.C. (2006) Pituitary pars intermedia dysfunction: challenges van der Kolk, J.H., Heinrichs, M., van Amerongen, J.D., Stooker, R.C., in of diagnosis and treatment. Proc. Am. Ass. equine Practnrs. 52, de Wal, L.J. and van den Ingh, T.S. (2004) Evaluation of pituitary 60-73. gland anatomy and histopathologic findings in clinically normal horses and horses and ponies with pituitary pars intermedia Schott, H.C., 2nd (2002) Pituitary pars intermedia dysfunction: equine adenoma. Am. J. vet. Res. 65, 1701-1707. Cushing’s disease. Vet. Clin. N. Am.: Equine Pract. 18, 237-270. Vick, M.M., Adams, A.A., Murphy, B.A., Sessions, D.R., Horohov, D.W., Sommardahl, C.S., Frank, N., Elliott, S.B., Webb, L.L., Refsal, K.R., Denhart, Cook, R.F., Shelton, B.J. and Fitzgerald, B.P. (2007) Relationships J.W. and Thompson, D.L., Jr (2005) Effects of oral administration of among inflammatory cytokines, obesity, and insulin sensitivity in the levothyroxine sodium on serum concentrations of thyroid gland horse. J. anim. Sci. 85, 1144-1155. hormones and responses to injections of thyrotropin-releasing hormone in healthy adult mares. Am. J. vet. Res. 66, 1025-1031. Vick, M.M., Sessions, D.R., Murphy, B.A., Kennedy, E.L., Reedy, S.E. and Fitzgerald, B.P. (2006) Obesity is associated with altered Tiley, H.A., Geor, R.J. and McCutcheon, L.J. (2007) Effects of metabolic and reproductive activity in the mare: effects of dexamethasone on glucose dynamics and insulin sensitivity in metformin on insulin sensitivity and reproductive cyclicity. Reprod. healthy horses. Am. J. vet. Res. 68, 753-759. Fertil. Dev. 18, 609-617. Tiley, H.A., Geor, R.J. and McCutcheon, L.J. (2008) Effects of Waller, A.P., Burns, T.A., Mudge, M.C., Belknap, J.K. and Lacombe, V.A. dexamethasone administration on insulin resistance and (2011a) Insulin resistance selectively alters cell-surface glucose components of insulin signaling and glucose metabolism in equine transporters but not their total protein expression in equine skeletal skeletal muscle. Am. J. vet. Res. 69, 51-58. muscle. J. vet. Intern. Med. 25, 315-321. Tinworth, K.D., Edwards, S., Noble, G.K., Harris, P.A., Sillence, M.N. and Waller, A.P., Kohler, K., Burns, T.A., Mudge, M.C., Belknap, J.K. and Hackett, L.P. (2010) Pharmacokinetics of metformin after enteral Lacombe, V.A. (2011b) Naturally occurring compensated insulin administration in insulin-resistant ponies. Am. J. vet. Res. 71, resistance selectively alters glucose transporters in visceral and 1201-1206. subcutaneous adipose tissue without change in AS160 activation. Biochim. Biophys. Acta 1812, 1098-1103. Tinworth, K.D., Boston, R.C., Harris, P.A., Sillence, M.N., Raidal, S.L. and Noble, G.K. (2011) The effect of oral metformin on insulin sensitivity in Yamagishi, S. (2009) Advanced glycation end products and insulin-resistant ponies. Vet. J. Epub ahead of print; doi:10.1016/ receptor-oxidative stress system in diabetic vascular complications. j.tvjl.2011.01.015. Ther. Apher. Dial. 13, 534-539.

Non-steroidal anti-inflammatory drug for intravenous that has not been previously diagnosed. Since many NSAIDs possess the potential Effectiveness: The effectiveness of EQUIOXX Injection was established in a use in horses only. to produce gastrointestinal ulcerations and/or gastrointestinal perforation, biocomparability study evaluating EQUIOXX Oral Paste and EQUIOXX Injection. concomitant use of EQUIOXX Injection with other anti-inflammatory drugs, such as Thus, additional field studies were not performed to support the effectiveness of CAUTION: Federal law restricts this drug to use by NSAIDs or corticosteroids, should be avoided. EQUIOXX Injection. Two hundred fifty-three client-owned horses of various breeds, or on the order of a licensed veterinarian. ranging in age from 2 to 37 years and weighing from 595 to 1638 lbs, were The concomitant use of protein bound drugs with EQUIOXX Injection for horses has randomly administered EQUIOXX Oral Paste or an active control drug in multi-center EQUIOXX Injection is administered for up Indications: not been studied in horses. The influence of concomitant drugs that may inhibit the field studies. Two hundred forty horses were evaluated for effectiveness and 252 to 5 days for the control of pain and inflammation associated with osteoarthritis metabolism of firocoxib Injection has not been evaluated. Drug compatibility should horses were evaluated for safety. Horses were assessed for lameness, pain on in horses. be monitored in patients requiring adjunctive therapy. manipulation, range of motion, joint swelling, and overall clinical improvement in a non-inferiority evaluation of EQUIOXX Oral Paste compared to an active control. Contraindications: Horses with hypersensitivity to firocoxib should not receive The safe use of EQUIOXX Injection for horses has not been evaluated in horses less EQUIOXX Injection. than one year of age, horses used for breeding, or in pregnant or lactating mares. At study’s end, 84.4% of horses treated with EQUIOXX Oral Paste were judged improved on veterinarians’ clinical assessment, and 73.8% were also rated Warnings: For intravenous use in horses only. Do not use in horses Consider appropriate washout times when switching from one NSAID to another intended for human consumption. improved by owners. Horses treated with EQUIOXX Oral Paste showed improvement NSAID or corticosteroid. in veterinarian-assessed lameness, pain on manipulation, range of motion, and joint Human Warnings: Not for use in humans. Keep this and all medications out of the Adverse Reactions: The effectiveness Adverse Reactions Seen in U.S. swelling that was comparable to the active control. reach of children. Consult a physician in case of accidental human exposure. of EQUIOXX Injection was established in a Field Studies with EQUIOXX Oral Paste Animal Safety: A target animal safety study was conducted to assess the safety biocomparability study demonstrating that Adverse Reactions EQUIOXX® n=127 Active Control n=125 Animal Safety: Clients should be advised to observe for signs of potential drug of EQUIOXX Injection followed by EQUIOXX Oral Paste in the horse. Thirty-two EQUIOXX Oral Paste is bioequivalent to EQUIOXX Abdominal pain 0 1 toxicity and be give a Client Information Sheet with each prescription. clinically healthy adult horses received EQUIOXX Injection intravenously once daily Injection. Thus, additional field studies were Diarrhea 2 0 Excitation 1 0 for five days at doses of either 0 mg/kg (control group); 0.09 mg/kg (1X); 0.27 For technical assistance or to report suspected adverse events, call 1-877-217- not performed to support the effectiveness of mg/kg (3X); or 0.45 mg/kg (5X the recommended dose). This was followed by once Lethargy 0 1 3543. EQUIOXX Injection. daily oral administration of EQUIOXX Oral paste for nine days at doses of either Loose stool 1 0 0 mg/kg (control group); 0.1 mg/kg (1X); 0.3 mg/kg (3X); or 0.5 mg/kg (5X the Precautions: Horses should undergo a thorough history and physical examination In controlled field studies, 127 horses (ages 3 to Polydipsia 0 1 37 years) were evaluated for safety when given recommended dose). This sequence (five days of EQUIOXX Injection followed by before initiation of NSAID therapy. Appropriate laboratory tests should be Urticaria 0 1 nine days EQUIOXX Oral Paste, for a total of 14 days) was repeated three times for conducted to establish hematological and serum biochemical baseline data before EQUIOXX® (firocoxib) Oral Paste for Horses at EQUIOXX Oral Paste was safely used concomitantly with a dose of 0.045 mg/lb (0.1 mg/kg) orally once a total treatment duration of 42 days (3X the recommended treatment duration and periodically during administration of any NSAID. Clients should be advised to other therapies, including vaccines, anthelmintics, and of 14 days). observe for signs of potential drug toxicity and be given a Client Information Sheet daily for up to 14 days. The following adverse antibiotics, during the field studies. with each prescription. See Information for Owner or Person Treating Horse reactions were observed. Horses may have Two male 5X horses demonstrated a white focus in the renal cortex which section of this package insert. experienced more than one of the observed adverse reactions during the study. correlated with tubulointerstitial nephropathy microscopically. The presence of tubulointerstitial nephropathy was considered treatment-related. Treatment with EQUIOXX should be terminated if signs such as inappetance, colic, The material safety data sheet (MSDS) contains more detailed occupational safety abnormal feces, or lethargy are observed. information. To obtain a material safety data sheet, please call 1-877-217-3543. One horse from the control group and two horses from the 5X group had injection site swellings during treatment. Injection site changes characterized by As a class, cyclooxygenase inhibitory NSAIDs may be associated with Information for Owner or Person Treating Horse: You should give a Client Information Sheet to the person treating the horse and advise them of the potential inflammatory cell influx and rarely tissue necrosis were seen in all study groups gastrointestinal, renal and hepatic toxicity. Sensitivity to drug-associated adverse including the control group. events varies with the individual patient. Horses that have experienced adverse for adverse reactions and the clinical signs associated with NSAID intolerance. reactions from one NSAID may experience adverse reactions from another NSAID. Adverse reactions may include erosions and ulcers of the gums, tongue, lips and There was a dose-dependent increase in the incidence of oral ulcers and erosions. Patients at greatest risk for adverse events are those that are dehydrated, on face, weight loss, colic, diarrhea, or icterus. Serious adverse reactions associated Elevated hepatic enzymes (GGT or AST) were noted in all study groups at one or diuretic therapy, or those with existing renal, cardiovascular, and/or hepatic with this drug class can occur without warning and, in some situations, result in more timepoints. One male 5X horse with an elevated GGT value on Day 42 was dysfunction. Concurrent administration of potentially nephrotoxic drugs should death. Clients should be advised to discontinue NSAID therapy and contact their noted to have tubulointerstitial nephropathy at the time of necropsy. For all horses, be carefully approached or avoided. NSAIDs may inhibit the prostaglandins that veterinarian immediately if any of these signs of intolerance are observed. The these hepatic enzyme elevations generally returned to the reference range by the maintain normal homeostatic function. Such anti-prostaglandin effects may result majority of patients with drug-related adverse reactions recover when the signs are next time point. in clinically significant disease in patients with underlying or pre-existing disease recognized, drug administration is stopped, and veterinary care is initiated.