Pharmacokinetics of TA and related changes in hydrocortisone were described following i.v., i.a., and i.m. administration. A single administration of TA has profound effects on secretion of endogenous hydrocortisone.

Pennsylvania (PA) State Racing Commissions regulate the endogenous androgenic steroid, testosterone (TES), in racing intact males (RIM) by quantification of TES in post-race samples. Post-race plasma samples (2209) collected between March 2008 and November 2010 were analyzed for TES, nandrolone (NAN), and other anabolic steroids (ABS). Of the 2209 plasma samples, 2098 had quantifiable TES ≥ 25 pg/mL. Plasma (mean ± SD) concentrations of TES and NAN in RIM were 329.2 ± 266.4 and 96.0 ± 67.8 pg/mL, respectively. Only 64.6% of RIM had quantifiable concentration of NAN, and there was no relationship between TES and NAN. Plasma TES concentrations were significantly (P < 0.0001) higher during the months of April, May, June, July, and August. A significantly higher (P < 0.006) plasma TES was observed in Thoroughbred (TB) (347.6 ± 288.5 pg/mL) vs. that in Standardbred (STB) (315.4 ± 247.7 pg/mL). Plasma concentrations of TES from breeding stallions (BS) were 601.6 ± 356.5 pg/mL. Statistically significant (P < 0.0001) lower plasma concentrations of the two steroids were observed in RIM horses. Based on quantile distribution of TES in the RIM and BS populations, 99.5% were at or below 1546.1 and 1778.0 pg/mL, respectively. Based on this population of RIM, the suggested upper threshold plasma concentration of endogenous TES in horses competing in PA should remain at 2000 pg/mL.

Compartmental models were used to investigate the pharmacokinetics of intravenous (i.v.), oral (p.o.), and topical (TOP) administration of dimethyl sulfoxide (DMSO). The plasma concentration-time curve following a 15-min i.v. infusion of DMSO was described by a two-compartment model. Median and range of alpha (t ) and beta (t ) half-lives were 0.029 (0.026-0.093) and 14.1 (6.6-16.4) hr, respectively. Plasma concentration-time curves of DMSO following p.o. and TOP administration were best described by one-compartment absorption and elimination models. Following the p.o. administration, median absorption (t ) and elimination (t ) half-lives were 0.15 (0.01-0.77) and 15.5 (8.5-25.2) hr, respectively. The plasma concentrations of DMSO were 47.4-129.9 μg/ml, occurring between 15 min and 4 hr. The fractional absorption (F) during a 24-hr period was 47.4 (22.7-98.1)%. Following TOP administrations, the median t and t were 1.2 (0.49-2.3) and 4.5 (2.1-11.0) hr, respectively. Plasma concentrations were 1.2-8.2 μg/ml occurring at 2-4 hr. Fractional absorption following TOP administration was 0.48 (0.315-4.4)% of the dose administered. Clearance (Cl) of DMSO following the i.v. administration was 3.2 (2.2-6.7) ml hr kg . The corrected clearances (Cl ) for p.o. and TOP administrations were 2.9 (1.1-5.5) and 4.5 (0.52-18.2) ml hr kg .