Excretion and metabolism of nikethamide in the horse.

It is well known that nikethamide (N,N-diethylnicotinamide, CoramineR) is metabolized very rapidly to nicotinamide. Hence, there is difficulty in proving that nikethamide has been used as a doping substance because nicotinamide is a normal physiological metabolite in the organism as well as a vitamin preparation. However, an intermediate metabolite (N-ethylnicotinamide) was found by us in the urine of horses treated with CoramineR. This was characterized by gas chromatography/mass spectrometry, and synthesized and identified as being N-ethylnicotinamide. The excretion and metabolism of nikethamide after intramuscular injection in the horse was followed using quantitative gas chromatography of urine extracts over a period of several hours and the results of these experiments are reported. Changes in urinary pH had no significant effect upon either the metabolism or rate of excretion of the drug.