Pharmacokinetic study of dipyrone metabolite 4-MAA in the horse and possible implications for doping control

The pharmacokinetic behaviour of dipyrone metabolite 4-MAA in serum was determined in seven horses of different breeds after a single intravenous dose administration. A biexponential formula was fitted to the serum concentration vs. time data. The median half-life of the elimination phase (t1/2 beta) was 4.85 h (range 5.04 h), the median volume of distribution (Vd(area)) was 1.85 L/kg (range 3.2 L/kg) and median of total clearance was 4.0 mL/min/kg (range 2.3 mL/min/kg).