Plasma concentrations and urinary excretion of nandrolone and/or its metabolites after intramuscular injection of nandrolone phenylpropionate to horses

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Abstract
A radioimmunological method was used as a screening procedure on horses to determine the period of detection or clearance time of therapeutic doses of the synthetic anabolic steroid, nandrolone phenylpropionate. Seven horses, either at rest or being exercised, were given a course of weekly i.m. injections of the steroid. On a separate occasion, some of the horses were given a single i.m. injection of the same compound. The weekly injections maintained a high plasma concentration of nandrolone and/or metabolites. The mean period of detection in plasma of these compounds was 23 (.+-. 2) days (range 21-25) in resting horses and 20 .+-. 6 days (14-27) in exercised animals. The mean period of detection in urine was 25 .+-. 7 days (16-32) and 25 .+-. 12 days (9-38) for resting and exercised horses, respectively. After a single i.m. injection to resting horses, the mean periods of detection were 12 .+-. 2 days (9-15) and 13 .+-. 2 days (11-16) in plasma and urine, respectively. In all experiments there was considerable individual variation in the time taken for the plasma and urine concentrations to return to predose values. This variation was particularly marked in the urine of exercised horses given a course of injections. With horses in training, this period may be > 5 wk, a period approaching the minimum of 42 days before a race, advocated by the Royal College of Veterinary Surgeons [England, UK], when the therapeutic use of anabolic steroids should be discontinued.