The effect of enzyme-inducing antiseizure drugs on the pharmacokinetics and tolerability of procarbazine hydrochloride

Purpose: Procarbazine hydrochloride (PCB) is one of the few anticancer drugs with activity against high-grade gliomas. This study was conducted to determine if the maximum tolerated dose and pharmacokinetics of PCB are affected by the concurrent use of enzyme-inducing antiseizure drugs (EIASD). Experimental Design: Adults with recurrent high-grade glioma were divided into cohorts who were (+) and were not (-) taking EIASDs. PCB was given orally for 5 consecutive days each month. Six patients were evaluated at each dose level beginning with 200 mg/m(2)/d and escalated using the modified continual reassessment method. Toxicity and response were assessed. Pharmacokinetic studies were done with a new electrospray ionization mass spectrometry assay. Results: Forty-nine patients were evaluated. The maximum tolerated dose was 393 mg/m(2)/d for the +EIASD group and the highest dose evaluated in -EIASD patients was 334 mg/m(2)/d. Myelosuppression was the primary dose-limiting toxicity. Significant hepatic dysfunction occurred in three patients in the +EIASD cohort. Four partial responses (8%) and no complete responses were observed. PCB exhibited linear pharmacokinetics with no significant differences between the two cohorts. A marked increase in peak PCB levels was noted on day 5 relative to day 1, which was not attributable to drug accumulation. Conclusions: This study suggests that (a) EIASD use does not significantly affect the pharmacokinetics of PCB; (b) changes in the peak plasma concentration of PCB, consistent with decreased apparent oral clearance due to autoinhibition of hepatic metabolism, occur with daily closing; and (c) severe hepatic dysfunction may accompany this administration schedule.