Antitumour activity and plasma kinetics of bleomycin by continuous and intermittent administration

We have studied the cytotoxicity of bleomycin (4--10 u/kg/day for 6 days) given by continuous i.p. infusion (using an osmotic minipump) compared to daily i.p. bolus administration, against P388 leukaemic spleen colony-forming-units(LCFU-S). Continuous i.p. bleomycin at 8 u/kg/day caused a 0.5 log greater reduction of LCFU-S than did an identical dose given by intermittent bolus administration. The infusion minipump provided constant bleomycin plasma levels of 0.62 +/- 0.03 mu/ml and a total plasma AUC (area under the plasma decay curve) of 89.0 mu.h/ml for 6 days at 8 u/kg/day. Intermittent bolus bleomycin at 8 u.kg/day had a terminal-phase plasma t1/2 of 15 min and a total 6-day plasma AUC of 90.8mu.h/ml. These pharmacokinetic data validate the osmotic minipump as a constant drug-delivery system, and suggest that the two administration schedules resulted in equal total bleomycin dosages. Although high peak bleomycin plasma levels (i.e. 32 mu/ml) were achieved with the intermittent bolus administration, continuous-infusion bleomycin's greater inhibition of LCFU-S was probably related to the drug's schedule-dependent cell-killing characteristics. The results of this study provide further rationale for the continuing use of infusion bleomycin schedules in cancer patients.