Managing Joint Disease in the Racehorse in the Face of Stricter Drug Restrictions
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IN-DEPTH: RACING-RELATED LAMENESS Managing Joint Disease in the Racehorse in the Face of Stricter Drug Restrictions C. Wayne McIlwraith, BVSc, PhD, Diplomate ACVS, ACVSMR Author’s address: Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; e-mail: [email protected]. © 2013 AAEP. 1. Introduction racing to protect equine health and welfare. Par- Intra-articular use of corticosteroids has become a ticipants included analytical chemists, veterinary recent focus (or re-focus) of attention in the Thor- pharmacologists, veterinary surgeons, racing regu- oughbred racing industry. The clinical use and sci- latory veterinarians, and practicing racetrack veter- entific basis of intra-articular corticosteroid inarians. Among the recommendations was a administration including catastrophic injury, artic- prohibition on intra-articular use of corticosteroids ular cartilage degradation, and the development of within 7 days of a race, taking into consideration the osteoarthritis (OA) as well as the timing of injection concerns expressed by many participants about the relative to racing have been reviewed.1 Most re- proximity of intra-articular injections to race day. cently, there has been very specific examination by The experts also recommended a 72-hour with- the Racing, Medication, and Testing Consortium drawal time for dexamethasone, a commonly used (RMTC). At the time of that press release, the short-acting corticosteroid that can be administered RMTC had approved (1) minimal withdrawal time intravenously, intramuscularly and orally. Other recommendations for corticosteroids on the basis of short-acting corticosteroids would have similar re- both recently completed work funded in part by the strictions. It was also noted that the recommenda- RMTC and conducted at the University of Pennsyl- tions would fundamentally change the use of vania, University of California-Davis, Kenneth L. corticosteroids in veterinary practice in racing in the Maddy Laboratory, and HFL Laboratory-Kentucky United States and therefore recommended a grace and other corticosteroid research conducted both in period to allow veterinarians time to adjust their the United States and abroad and (2) recommenda- veterinary practices and to allow trainers time to tions were developed during an RMTC-hosted Cortico- adjust their training practices to comply with the steroid Experts Conference in Anaheim, California, on new regulations. Further details regarding these November 30, 2012. This meeting brought together recommendations are discussed below (Table 1). qualified individuals with professional expertise in The purpose of this review is to offer possible key areas with the goal of providing a comprehen- modifications and alternatives with the intra-artic- sive plan for regulating corticosteroid use in horse ular and systemic therapy for traumatic joint injury NOTES 436 2013 ր Vol. 59 ր AAEP PROCEEDINGS IN-DEPTH: RACING-RELATED LAMENESS Table 1. Corticosteroid Threshold Chart Withdrawal Time for 95/95 Minimum Experimental Tolerance Interval at Withdrawal Route of Administration Experimental Dose and Medication Threshold Time* Administration† Dosage‡ Route of Administration Betamethasone 10 pg/mL of 7 Days Intra-articular Total of 9 mg of 7 Days plasma or betamethasone (as a serum mixture of betamethasone sodium phosphate and betamethasone acetate) in one joint Dexamethasone 5 pg/mL of 3 Days Intravenous, 0.05 mg/kg of 3 Days plasma or intramuscular, dexamethasone (as serum and oral dexamethasone sodium phosphate) Isofluprodone TBD TBD Intra-articular 20 mg total dose of Pending isoflupredone (as isoflupredone acetate, Predef 2X) in one joint Methylprednisolone 100 pg/mL of 7 Days Intra-articular Total of 100 mg of 21 Days plasma or methylprednisolone serum (as methylprednisolone acetate) in one joint§ Prednisolone TBD TBD Intravenous and Pending oral Triamcinolone 100 pg/mL of 7 days Intra-articular Total of 9 mg 7 Days acetonide plasma or triamcinolone serum acetonide in one joint *The RMTC has recommended a 7-day regulatory withdrawal time for all intra-articular use of corticosteroids, recognizing that the clearance times for some will be longer than 7 days. Furthermore, this regulation is not in conflict with the withdrawal time for dexamethasone listed here; the use of dexamethasone intra-articularly is inappropriate because it would be considered off-label and a violation of the provisions of the Animal Medicinal Drug Use and Clarification Act (AMDUCA). †Route of administration: Administration of these corticosteroids by other routes of administration may affect the length of time it takes before the medication is below the regulatory threshold (eg, betamethasone injected intramuscularly takes approximately 33 days for its plasma concentration to fall below the regulatory threshold). The withdrawal times for betamethasone, methylpred- nisolone, and triamcinolone acetonide apply to the intra-articular route of administration only and should not be interpreted as guidance for withdrawal of these substances after other routes of administration. ‡Administration dosage and related 95/95 withdrawal times: This is provided as guidance and does not constitute a guarantee. It does not account for repeat dosage, multiple articular site dosage, the effects of combining other medications with these corticosteroids, or different dosages from those listed here. A risk assessment must be done by the veterinarian and trainer to determine protocol that complies with the prohibition against administration of an intra-articular dose within 7 days of racing. §Please note that for this dose of methylprednisolone acetate, a 21-day period from administration to racing is recommended to ensure that the medication is below the regulatory threshold. The minimum withdrawal time in this case anticipates the possibility of lower doses being used and assumes that these lower doses may decrease the length of time required for the concentration of the medication to fall below the regulatory threshold. and OA in the horse. Other countries have trav- regarding a series of experimental studies with in- eled down this pathway some time ago. More clear tra-articular therapy. restrictions on the use of medication should be con- After review of the data and addition of a toler- sidered in the positive light that at the same time, ance interval for safety, the RMTC was able to cal- there has been validation of non-corticosteroid treat- culate a recommended withdrawal time with the ments even in the acute stage of joint inflammation experimental dose of 100 mg of intra-articular meth- and newer biological therapies have emerged that ylprednisolone acetate (MPA) in one articular space, have no side effects and offer positive advances. on the basis of a 95/95 tolerance interval, requiring approximately 16.6 days for the concentration of 2. Intra-Articular Corticosteroids: What Has MPA in plasma or serum to fall below the 100 pg/mL Changed? threshold. This was rounded out to 21 days. In As discussed above, the RMTC issued a 7-day limi- February 2012, Mid-Atlantic regulators, horsemen, tation for long-acting corticosteroids so that they and industry representatives met to discuss the im- would fall below their respective threshold levels plementation of numerous medication guidelines, AAEP PROCEEDINGS ր Vol. 59 ր 2013 437 IN-DEPTH: RACING-RELATED LAMENESS including the corticosteroid recommendations, on a signs were seen with HA compared with that in regional uniformed basis. Numerous regulators control horses, but, histologically at day 70, there and horsemen expressed concerns regarding the dis- was significantly less fibrillation with HA treatment parity between the 7-day ban on intra-articular use compared with that in controls. The place for HA of MPA and the 21-day recommendation for the ex- in combination therapy is therefore not as an acute perimental dose to comply with the proposed regu- anti-inflammatory but as a long-term disease-modi- latory threshold. There was a feeling from fying osteoarthritis drug (DMOAD). veterinarians as well that compliance with the rec- ommendations would be difficult and could place 5. Polysulfated Glycosaminoglycan horsemen and veterinarians attempting to comply Work examining the effect of intra-articular polysul- with the recommendations in good faith in “harm’s g way” and that the better approach may be to ban the fated glycosaminoglycan (PSGAG) suggests that drug and recommended use of alternative therapies. this product has significant effects on acute synovi- tis and can be used in lieu of intra-articular cortico- To continue the principal goal of the RMTC in hav- 4 ing regulatory thresholds adopted and uniformity steroids. In a controlled study with the use of the attained, a decision was made to remove methyl- equine osteochondral fragment–OA model, eight prednisolone from the list of approved therapeutics. horses received PSGAG (250 mg) and amikacin sul- fate (125 mg) intra-articularly at 14, 21, and 28 days 3. Working Within the 7-Day Rule after induction of OA, and eight control horses re- As discussed in an earlier review,1 controlled studies ceived 2 mL of saline (0.9% NaCl) solution and ami- have been performed in the horse to clarify thera- kacin sulfate (125 mg) intra-articularly on study peutic response as well as deleterious effects for days 14, 21, and 28. The degree of synovial mem- betamethasone esters,a