The effect of verapamil on the pharmacokinetics of adriamycin
The concurrent administration of adriamycin (intravenous) and verpamil (oral) is of considerable interest because of experimental data suggesting that resistance to adriamycin may be overcome by this means. The potential for a pharmacokinetic interaction between the two drugs has therefore been investigated in five patients with small cell lung cancer treated with combination chemotherapy comprising adriamycin, VP16, vincristine and cyclophosphamide. The data indicate that a significant interaction takes place. Adriamycin peak levels, terminal halflife and the volume of distribution at steady state are higher, whereas plasma drug clearance and the volume of the central compartment are lower with co-administration of verapamil. There was no evidence of enhanced drug toxicity in this study; however, the data should be considered in the interpretation of clinical trials in which adriamycin and verapamil are used together, both in terms of toxicity and tumour response.