Pharmacokinetic parameters of 14C oxithiopurinol in rat

The study with labelled compound has shown that in rat, as in man, thiopurinol is primarily and rapidly converted into oxithiopurinol. More than 80% of the radioactivity of plasma was identified as oxithiopurinol less than 10 minutes after intravenous or oral administration. The parameters of oxithiopurinol were estimated from the decline of radioactivity in blood from 5 minutes to 8 hours after intravenous administration of 4 microCi/100 g of thiopurinol (8 animals) or oxithiopurinol (5 animals). Half lives of oxithiopurinol t 1/2 (beta) were 2.52 +/- 0.78 hr and 2.90 +/- 1.00 hr and clearance 2.00 +/- 0.36 ml/min. and 3.38 +/- 0.69 respectively. Estimate of renal clearance for oxithiopurinol in rat was 4,17 ml/min. The rapidity of hydroxylation and of elimination of oxithiopurinol might be assumed to be the cause of the apparent ineffectiveness of thiopurinol in vivo on xanthine oxidase activity.