The bioavailability in man of ICRF-159 a new oral antineoplastic agent.

The bioavailability of the antineoplastic agent, ICRF-159, has been examined in 12 patients receiving the drug in single and subdivided dose schedules in an attempt to account for the differences in toxicity found with the different schedules clinically. Recovery of radioactivity in the urine after single large doses (13.3-19.4 g) was 8.5 +/- 3.0% of the administered dose. After doses of 3.8-5.55 g recovery was 22.7 +/- 10.5% and after the same dose subdivided into 3 equal aliquots it was 52 +/- 8.7%. Unrecovered radioactivity was largely accounted for in the faeces. Plasma radioactivity levels in 2 patients after high and low dose were equivalent. Toxicity of the drug paralleled urinary recovery of radioactivity. It is concluded that schedule dependence of toxicity of ICRF-159 is at least partly due to bioavailability factors.