Prednisolone Also Binds to Transcortin • Other Synthetic GS Only Bind to Albumin

PK/PD considerations for corticosteroids

P L Toutain, National Veterinary School, Toulouse, France Wuhan October 2015

1 Anti-inflammatory drugs

Corticosteroids NSAIDs

• Glucocorticosteroids (GCS) are broad and potent anti- inflammatory drugs. • They are extensively used to mitigate or suppress inflammation associated with a variety of conditions especially joint and respiratory system inflammation. • GCs are not curative: • GCs are only palliative symptomatic treatments and chronic use of GCs can be, in fine , detrimental • GCs possess many other pharmacological properties (not reviewed in this presentation)

3 The cortisol or hydrocortisone

4 Cortisol : An endogenous hormone and a surrogate endpoint of the duration of the GCS effects; it physiology should be understood to use properly GCS

5 Cortisol synthesis • All GCs used in therapeutics are synthetic derivatives of cortisol. • Cortisol (hydrocortisone) is synthesized in the adrenal cortex and it is the main corticosteroid hormone in most species.

6 Steroids synthesis by the adrenal gland

Aldosterone

Cortisol

Androgens

Epinephrine (adrenalin)

7 Cortisol ou Hydrocortisone structure – activity relationship Three structural properties are required for a GC activity (i.e. for cortisol to bind to GC receptor)

8 Cortisol (hydrocortisone)

• Minimal information on cortisol physiology (secretion, distribution & elimination ) needs to be known to understand the clinical pharmacology of GCS

9 Plasma cortisol

• Cortisol levels are very different in domestic species • Pattern of secretion – Circadian rhythm (h) – Pulsatilty (minute)

10 Plasma cortisol level Plasma concentration (ng/mL) 600

500

400

300 Series1

200

100

0 1 2 3 4 5

11 Plasma cortisol levels: circadian rhythm & pulsatility

Toutain et al. Domestic.Anim.Endocrinol. 1988, 5:55 12 All dogs Rest dogs

13 Plasma cortisol levels: circadian rhythm & pulsatility

• The cortisol secretion is pulsatile with minute- to-minute variations in the plasma cortisol concentrations making the interpretation of snapshot plasma samples difficult.

14 Modeling of circadian cortisol

15 Binding of cortisol to plasma proteins

• In mammalian plasma, cortisol binds to a specific alpha-glycoprotein: corticosteroid-binding globulin (CBG). • Binding to CBG is saturable (Bmax)

B max Free Total  Free   NS  Free Kd  Free

16 Binding of synthetic GCS to plasma protein • Prednisolone also binds to transcortin • Other synthetic GS only bind to albumin

Prednisolone cannot be used for an adrenal suppression test

18 Adrenal suppression test Prednisolone vs. Dexamethasone (IV)

Prednisolone (600µg/kg) Dexamethasone Immediate decrease of cortisol due (50µg/kg) to the displacement of cortisol Delayed decrease due to the from the CBG by prednidsolone suppression of ACTH secretion

Cortisol concentration (ng / ml) Cortisol concentration (ng / ml) 100

80 80 60 60 40 40 20 20 0 0 0.25 0.5 1 2 4 8 12 24 48 0 0 0.16 0.5 1 2 3 4 6 24 48 72 96 Hours Hours 19 Toutain et al., Am.J.Vet.Res 1985, 9: 1750 Urine cortisol

• The advantage of urine cortisol is due to the fact, that unlike plasma sample, a snapshot urine sample is representative of the total cortisol secretion over the entire preceding period of time separating two micturitions, i.e. it is not subjected to time-to-time variation like plasma cortisol.

20 Urine cortisol

• Diagnostic of Cushing syndrom

)

6 3000 - 1000 300 100 30 10

3 Rapport : : Rapport 1 0.3 healthy dogs with dogs with cortisol/créatinine (x10 cortisol/créatinine dog hyperadrenocorticism polyuria/polydipsia Urine Cortisol : cushing : 118 ± 15 ng/mL; Sensitivity of the test 100%. Spécificity= 22% (confusion with dogs having a poluuric/polydipsic syndrom Cortic 00.21 Feldman, JAVMA 1992, 200 : 1637 Urine cortisol (doping control) • International threshold: 1µg/ml or 1000ng/mL

22 Urine cortisol Population investigations (n=254)

Average 48ng/mL (geometric) maximum 388

Probability Urine exceeding concentration ng/ml 10-3 611 10-4 1025 10-5 1606

Popot & al EVJ 1997 29 220-229 23 Regulation of cortisol secretion to be understood to predict the suppressive effect of GCS

24 Suppressive effect of corticosteroids on the hypothalamic pituitary adrenal axis (HPA)

SNC

ACTH CRF • Stimulation of cortisol synthesis (no storage) ACTH • Trophic action on the ACTH zona fasciculata and reticularis

CORTISOL

Cortic 00A.26 Suppressive effect of synthetic GC

Control Short term Long term

SNC SNC SNC

CRF CRF CRF - - ACTH ACTH CS ACTH

ACTH ACTH ACTH

COR COR

t t Cortic 00A.27 Cortisol bind to specific receptor

Inactive glucocorticoid receptors (GR) are located in the cytoplam; after binding to cortisol, the GR is activated and translocated into nucleus; then, GR bind the glucocorticoid response element (GRE) in the DNA and regulate the responsive gene (activation). The GR can also inhibit transcription by a direct protein/protein interaction 28 Corticosteroid Mechanism of action

Lipocortin Corticoids +

Plasma membrane Inhibition of phospholipase A2 PLA2 (PLA2) NSAIDs

Arachidonic acid

cyclooxygenases lipoxygenase

PG, TXA2 Leucotrienes

Ferguson In: Adams, 1995 Cortic 00A.29 Métabolisme du cortisol

CH2 O H

20 et 20ß dihydrocortisone 20ß dihydrocortisol HOCH CH3 ...... OH HO 11 ß - CH3 deshydrogénase CH2 O H CH2 O H Cortisone CORTISOL C = O C = O O CH3 ...... OH CH3 ...... OH HO O CH3 CH3

O O 6ß hydroxycortisol

CH2 O H 11-Ketoetiocholanolone 11ß - hydroxy C = O O etiocholanolone O CH CH3 ...... OH 3 CH3 HO O HO

CH CH3 3 CH3

HO HO O H H OH 32 Cortisol metabolism is used as a biomarker of drug metabolism (polymorphism associated to CYP3A)

33 Corticosterioids - Filiation -

34 Synthetic glucocorticosteroids (GCs)

• Chemical modification of cortisol have generated derivatives with: – Greater separation of glucocorticoid and mineralocorticoid activity(selectivity) – Higher potency – Longer duration of action • Chemical modification of cortisol do not have generated derivatives with: – Separation of AI effect from effect on carbohydrates, lipids and proteins metabolism or without adrenal suppression

The main CS used in veterinary medicine for systemic administration • Prednisolone • Méthylprednisolone • Dexaméthasone • Triamcinolone acétonide • Fluméthasone • Isoflupredone

Cortic 00A.36 The main CS used for systemic inhalation

Fluticasone propionate

Beclométhasone 17 monopropinate

Budesonide

Cortic 00A.37 The two main group of CS

Cortisol

Non halogenated - Halogeneted- derivatives derivatives

No mineralocorticoid activity Prednisolone With mineralocorticoid Dexmethasone, Methylprednisolone activity betamethasone budenoside Isoflupredone triamcinolone acetonide betamethasone

38 Synthetic derivatives of cortisol

• All therapeutic GCs have a 21-carbon cortisol skeleton • A variety of GCs have been developed to increase the potency of the anti- inflammatory effect and to decrease or even suppress the mineralocorticoid effects of cortisol

39 Cortisone Δ Prednisone GC filiation C6 CH3 C11 C11 OOH OOH Methylprednisone C11 OOH

Methylprednisolone

C6 C16 & C17 Triamcinolone acetonide CH3

OH - TRIAMCINOLONE C16 Cortisol Δ Prednisolone C9 F Fluoro- CH3 - Dexamethasone prednisolone - Betamethasone (Predef 2X)

C6 C16 PROPERTY C9 CH3 - Flumethasone

ANTI-INFLAMMATORY - GLUCOCORTICOID

MINERALOCORTICOID

40 The 2 main PD parameters:

Emax ED50/EC50 Emax 1 1 1 2 Emax 2 2

EC501 EC502

Efficacy Potency

Issue for analysts Issue for vets Potent drug=low LOQ ECVPT Toulouse 2009 - 44 Relative potency of corticosteroids

glucocorticoïd Minéralocorticoïd Substances Duration action action action Cortisol 1 1 12h Prednisolone 5 0.8 24h Méthylprednisolone 5 0.8 24h Isoflupredone 25 25 48-72h Triamcinolone 5 0 24h Triamcinolone acétonide 30 0 48-72h Dexamethasone 25 0 48-72h betamethasone 25 0 48-72h Flumethasone 120 0 48-72h

Order of potency of the different corticoids is now internationally accepted and cannot be reconsidered even if there are some discrepancies in the literature 47 Relative anti-inflammatory (AI) potency of topical GC used for inhalation (1=dexamethasone)

Substances AI Potency Comments (1=dexamethasone) Beclomethasone 0.5 A prodrug of dipropionate beclomathasone monopropionate Beclomethasone 17- 13 Active moiety of monopropionate beclomethasone dipropionate Beclomethasone 0.5 Metabolite of beclomethasone monopropionate Fluticasone propionate 18 Active substance Budesonide 9 Triamcinolone acetonide 50

48 Corticoïds : esters & Formulations

49 Corticoïdes : Substance active vs. esters

Substances (principes actifs)

Esters alcohol (prodrogues)

Non Hydrosolubles hydrosolubles

50 Most GCs are administered as esters

substance

Hydrosoluble Non hydrosoluble (IV) (depot)

Phosphate Acetate Succinate Butyrate ………. ………

52 Most GCs are administered as esters

• Most GC are administered as esters, • Esterification considerably alters the disposition and duration of the GC action. – Esterification with a monoacid (like acetic acid) at C- 21 gives non-hydrosoluble drugs that can be used as long-acting formulations when administered by the intramuscular, subcutaneous or IA routes. – Esterification of the same parental drug by a diacid (such as succinic acid) can give a hydrosoluble ester enabling a salt to be formed (e.g. a sodium succinate). Phosphate esters are also hydrosoluble.

53 Formulations of corticoïds

Méthylprednisolone (medrol)

CH2 OH C = O CH ...... OH HO 3

CH3 Methylprednisolone Methylprednisolone sodium succinate acetate O C22H30O5= 374,5 (Solumedrol®) CH3 (Dépomedrol®)

CH2 O - CO - CH3 CH2 - O - CO - (CH2)2 - COONa C = O C = O CH3 ...... OH CH ...... OH HO HO 3 CH 3 H CH3 H H O C23H30O6 = 402,5 O C26H33O8Na = 396,5 CH3 CH3 54 Corticoids

Esters Esterification en C21 et/ou C17 des OH Par des monoacides : formes insolubles

- acetate ( 21-acétate) - dimethylbutyrate (21) - phenylpropionate - dipropionate ( C17 , C21) - valerate, pyvalate - benzoate ( C17 )

Cortic 00A.55 Esters are prodrugs

• Practically all esters except beclomethasone 17-monoprpionate and fluticasone propionate are inactive prodrugs and have to be hydrolyzed to release their active moiety because an OH radical at C-21 is necessary for the binding of corticoids to their cellular receptors.

56 Near all ester are prodrugs Prednisolone & prednisolone acetate

Hydrolysis

Prednisolone Prednisolone acetate A prodrug 57 Hydrolysis by esterases

• Hydrolysis by esterases may occur either in different body fluids such as blood or synovial fluid (as for methylprednisolone acetate for which the half-life is about 1h in synovial fluid) or mainly in liver (as for succinate), meaning that for a local administration, the judicious selection of an appropriate ester is in order

58 Fluticasone propionate & beclomethasone monopropionate are not prodrugs

Beclomethasone 17,21 dipropionate • Fluticasone propionate A prodrug Active drug

Beclomethasone 17-monopropionate Active drug 59 Corticoïds : Route of administration

60 Route of administration

systemic Local

GCS also use for GC specifically developed IV, PO, IM….. systemic administration for local administration

Intra-articular Percutaneous inhalation Intramammary

61 PK of corticoids

62 Disposition of méthylprednisolone

• Méthylprednisolone succinate (MPS) vs. méthylprednisolone acetate (MPA)

Plasma Concentration (ng / ml) Plasma Concentration (ng / ml) 105 30 20 MPA 104 MPS 10 103 MP 5 102 0 10 0 60 120 240 360 480 min 0 40 80 120 160 200 240 280 hours Toutain et al. J.Pharm.Sci 1986., 75,251Cortic 00A.63 Prednisolone succinate vs. prednisolone acetate • illustrates the differences between the disposition of prednisolone after administration of prednisolone succinate by the IV and IM routes and after prednisolone acetate administration by the IM route.

64 Disposition of prednisolone: hydrosuble vs. Unsoluble formulation (0.6 mg/kg)

Prednisolone Prednisolone acetate 104 sodium succinate 20 15 103 10 IM 6 102 IM IV 10 2

0 2 4 6 8 10 0 24 48 72 96 144 Concentration (ng / ml) / (ng Concentration Heures

Toutain et al. Am.J.Vet.Res 1985, 46:719-725 Cortic 00A.65 Pharmacokinetic parameters of GCs

Substances CL Vd HL F% (mL/kg/min) (mL/Kg) (h) Hydrocortisone 2.28 229 1.55 (tritiated cortisol) Hydrocortisone 2.56 600 10.1 (after HC succinate,1g) Prednisolone 3.91 561 1.65 IM:92 Methylprednisolone 15 3600 2.85 Dexamethasone 7.33 2060 10.7 Triamcinolone 8.1 5300 12 acetonide

66 DXM disposition: rest vs. exercise

Clearance: -25% VSS:-17% Half-life: no change

67 Adrenal suppression: Plasma cortisol levels and synthetic corticoid treatment

68 Adrenal suppression of cortisol secretion by synthetic GCs • Synthetic GC are able to inhibit the production of cortisol – negative feedback on ACTH secretion. • The duration of the AI effect Cortisol Synthetic GC of a synthetic GC for a systemic administration is generally similar to the duration of suppression of endogenous cortisol

69 Adrenal suppression of cortisol secretion by synthetic GCs

• It should be stressed that adrenal suppression is not only associated with a given substance but also with a particular ester of that substance and for a particular ester, the route of administration and the administered dose.

70 Adrenal suppression Prednisolone vs. Dexamethasone (IV)

Prednisolone Dexamethasone (600µg/kg) (50µg/kg) Short action Longer duration of action Cortisol concentration (ng / ml) Cortisol concentration (ng / ml) 100

80 80 60 60 40 40 20 20 0 0 0.25 0.5 1 2 4 8 12 24 48 0 0 0.16 0.5 1 2 3 4 6 24 48 72 96 Hours Hours 71 Toutain et al., Am.J.Vet.Res 1985, 9: 1750 Adrenal suppression of prednisolone (600µg/kg) succinate vs. Acetate (IM)

Succinate (IM) Acetate (IM) Short action long action

Cortisol concentration (ng / ml) 100

0 0 0.25 0.5 1 2 4 8 12 24 48 Hours days Toutain et al., Am.J.Vet.Res 1985, 9: 1750 72 Duration of adrenal suppression (IV route)

Substances Anti-inflammatory Mineralocorticoid Adrenal suppression potency potency (h, days)

hydrocortisone 1 1 About 24h Hydrocortisone 0 0 A prodrug of cortisol hemisuccinate Prednisolone 5 1 About 24h Methylprednisolone 5 1 About 24h isoflupredone 25 25 No data Triamcinolone 5 0 No data Triamcinolone 30-50 0 24h acetonide Dexamethasone 25 0 72-96h Betamethasone 25 0 Likely similar to DXM Flumethasone 120 0 Likely longer than for DXM 73 Adrenal suppression of cortisol secretion by synthetic GCs

• For local administrations, the fraction that gains access to the blood can be too low to impact on the adrenal gland function.

74 Adrenal suppression for an intra-articular methylprednisolone acetate administration

Autefage et al., Equine Vet J 1986

75 IC50 for cortisol suppression

Substances IC50 (ng/mL) Cortisol 8 Prednisolone 1.2 Methylprednisolone 0.52 Dexamethasone 0.17

• (Mager et al., 2003) 78 Corticosteroid esters and local routes of administration

79 Intra-articular administration

Cortic 00A.80 Intra-articular administration

• Two technical issues: – Selection of a joint; – Technic of administration: • Blind or not?,

81 Pro: mostly of non scientific nature – To help the horses perform the job they were bred for and to prolong their careers and lives – Postoperative administration may be beneficial in protecting the cartilage and improving the cosmetic appearance of the joint

82 CONS: mostly of scientific nature and rather well documented

– Lack of curative effect – joint flare – Risk for further injury – Articular cartilage degenerative/steroid chondropathy

Heathrow EHLSC 2008 Musculoskeletal injury following local corticosteroid injection in Thoroughbred racehorses

• Veterinary records for 1911 thoroughbred • Thoroughbred racehorses receiving local corticosteroid injection (LCI) suffer musculoskeletal injury MSIs at approximately 4.5 times the rate of horses not receiving treatment, and for horses receiving multiple LCI the rate is approximately twice that of horses receiving single LCIs.

Whitton, C., et al 2012Faculty of Veterinary Science, University of Melbourne, Victoria, 3030, Australia. 84 Accuracy of IA administration: blind vs. ultrasound-guided injection

85 Disposition of methylprednisolone in the synovial fluid

• Disappearance of MPA within 6 days but a persistence of its active moiety for 5 to 39 days depending on the horse. The terminal half-life of MP was between 81 and 261h:

86 Origin of the sustained release of MP after a MPA administration

• the reason for the persistence of MP was most likely due to a precipitation of MPA that adhers to the synovial membrane and most likely acts as a foreign body. • This likely explains why MPA is not well tolerated in horses (McIlwraith, 2010) and that other GC are now preferred for IA administration, namely betamethasone esters and triamcinolone acetonide

87 IA disposition of methylprednisolone (MP) in synovial fluid after an methylprednisolone actate administration (MPA, Dépomédrol® ) (200 mg in toto)

5 10

4 10

MP synovial fluid fluid MP synovial concentration (ng ml) / concentration 2 10

30 10 20 40 60 80 100 (Days)

88 Adrenal suppression following a methylprednisolone actate (200mg in toto) IA administration in cattle assesssed by a series of ACTH tests

60 Return to control value needs 3 months

HYDROCORTISONE plasmatique (ng / ml) / (ng plasmatique HYDROCORTISONE 0 Contrôle 0.14 1 2 4 6 8 10 12 Semaines Cortic 00A.89 Triamcinolone acetonide

Mean synovial Triamcinolone acetonide (TA) concentration (ng/mL) vs. time (h) in the metacarpophalangeal joint after an administration of TA at a dose of 9mg in toto (16µg/kg

Data were fitted with a biexponential equation to give the terminal half-life of TA in synovial fluid as 20.2h with an overall mean residence time of 13.8h.

(redrawn from raw data of Kay et al. (Kay et al., 2008) 91 Inhalation

93 Inhaled Corticosteroids : indications

1. Airways inflammation 2. Recurrent airways obstruction ou RAO or heaves) • (formally named COPD)

94 Why inhalation?

• To ensure selectivity (no other effect) – Long-lasting treatments • Specific GCS were developped for this application – Highly potent (small volume) – Slow eliminated from the airways – High systemic clearance for the absorbed fraction

95 Inhaled Corticosteroids (ICS)

• Inhaled corticosteroids (ICS) are now considered the first-line therapy in treating asthma and are approved for chronic use in children as young as 12 months of age.

96 Many devices: are they equivalent?

Cortic 00A.97 Relative anti-inflammatory (AI) potency of topical GC used for inhalation (1=dexamethasone)

99 Disposition of GG after inhalation

Inhalation

Atmosphere Swallowing Lung Digestive tract disposition User safety Possible Adrenal Possible Adrenal suppression suppression

Yes for beclomethasone No for fluticasone

100 Inhalation treatment: an user safety issue?

• During exhalation, some degree of air pollution of the drug was evident and user safety was accounted for by ventilating the room sufficiently during administration • Q: Do we have a part of liability if releasing DT for inhalation while no marketing authorization exist in case of difficulties for staff who are at high risk of adverse effects from exposure (e.g, pregnant women or those with demonstrated sensitivity to the specific agent).

102 Systemic disposition of inhaled GS

• Drug deposited in the oropharynx, in up to 80% of horses and does not contribute to the therapeutic effect but is swallowed and contributes to the systemic exposure with possible systemic side effects. • Inhaled GC are well absorbed by the lung parenchyma but have a rather low or very low bioavailability when ingested.

103 Pharmacodynamic of inhaled GS

• Such a progressive establishment of clinical effects and return to pretreatment status makes it difficult or even impossible to establish any PK/PD relationship useful for drug monitoring. • In addition, the dose-effect relationship is flat and difficult to establish.

108