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EQUINE VETERINARY EDUCATION / AE / MARCH 2016
TABLE 1: Time at which corticosteroid concentrations fell below the ARCI regulatory threshold following administration of various clinical doses of triamcinolone acetonide, methylprednisolone acetate, isoflupredone acetate and betamethasone to a total of 58 Thoroughbred racehorses
Time until below ARCI regulatory threshold Drug Methylprednisolone acetate (n = 24)
Dose range (mg) No. joints 80
Trimacinolone acetonide (n = 17) Isoflupredone acetate (n = 7)
Betamethasone (n = 10)
40–200 300–400 160–600 9–12
12–18 10–18 12
10–16 30–60
1 2 3 4 1 2 2 3 4 2
TABLE 2: Time at which corticosteroid concentrations fell below the ARCI regulatory threshold when administered in combination with other noncorticosteroid intra-articular medications to Thoroughbred racehorses
Corticosteroid
Hyaluronic acid (22 mg)
Polyglycan (2.5–3 ml)
Polyglycan (5 ml)
Polyglycan (3–4 ml)
MPA TCA
No. joints
2 4 2
Betamethasone 2 Betamethasone 2
Betamethasone 2 TCA
1 2
Dose (mg)
Time when below RCI proposed threshold
40–80 Day 7 (4/4) 160 Day 10 (1/1) 12 Day 7 (9/9) 12 Day 7 (3/3)
30 Day 7 (3/4) Day 10 (4/4)
60 Day 10 (2/2)
9 Day 7 (1/1) 18 Day 7 (1/1)
administration to QH, are listed in Table 3. Serum concentrations fell below the threshold (100 pg/ml) by Day 7 for both TCA (2–40 mg dose) and IPA (2–30 mg dose) administration. For betamethasone (12–42 mg), all horses had serum concentrations below the regulatory threshold (10 pg/ ml) by 7 days post administration. Following administration of MPA (9–40 mg), serum concentrations were below the regulatory threshold (100 pg/ml) by Day 10 post administration.
Discussion
The goal of the current study was to assess the applicability of current regulatory thresholds and withdrawal time guidance for the most commonly administered IA corticosteroids following the use of a variety of clinical dosing regimens. Current regulatory guidance for the use of IA corticosteroids in racehorses are based upon studies of a single dose administered in a single joint. It is not possible to study every corticosteroid dosing regimen employed by veterinary practitioners, but this study provides veterinary practitioners with threshold compliance information on a broad and clinically relevant variety of corticosteroid treatments.
© 2016 EVJ Ltd Drugs Betamethasone (n = 3)
Isoflupredone + Betamethasone (n = 29)
MPA + Betamethasone (n = 1) TCA + Betamethasone (n = 3)
TCA + Isoflupredone + Betamethasone (n = 24)
MPA + Isoflupredone + TCA + Betamethasone (n = 17)
TCA + MPA + Isoflupredone (n = 3)
TCA + MPA + Betamethasone (n = 2)
Day 7 Day 10 Day 14 Day 17 Day 21 1/1
6/11 5/5
12/12 3/3 2/2 2/2
7/10 10/10
TABLE 3: Time at which corticosteroid concentrations fell below the ARCI regulatory threshold following administration of various combinations of clinical doses of triamcinolone acetonide, methylprednisolone acetate, betamethasone and isoflupredone acetate to a total of 82 Quarter Horse racehorses
Dose range (mg)
12–24
Time until below RCI regulatory threshold
Day 7 Day 10 3/3
4–26 29/29 12–42 29/29 40 24
10–20 6–12
10–24 24/24 2–20 24/24 6–36 24/24
20–40 16/17 17/17 5–30 17/17
10–40 17/17 6–30 17/17 2–20
20–40 8–25
20–40 20–40 18–30
3/3 3/3 3/3 2/2 2/2 2/2
In the presently reported study, TCA serum concentrations
fell below the regulatory threshold (100 pg/ml) by 7 days post intra-articular administration at all doses studied. This was true whether TCA was administered as the sole treatment or in combination with other corticosteroids. This is in agreement with previous studies (Soma et al. 2011; Knych et al. 2013) describing the administration of 9 mg (Knych et al. 2013) or 20–30 mg (Soma et al. 2011) of TCA into a single antebrachiocarpal joint. Similarly, following administration of 6 mg of TCA into both tarsometatarsal joints (total dose of 12 mg), serum concentrations were less than 100 pg/ml by 7 days post administration (Knych et al. 2011). Although its use is somewhat controversial (McIlwraith 2010), MPA is arguably one of the more commonly used
1/1 1/1 3/3 2/3
10/11 3/4 3/8
11/11 4/4 5/8 8/8
3/3
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