Pharmacokinetics of oral contraceptive steroids following the administration of the antimalarial drugs primaquine and chloroquine.

The effects of a single dose of two antimalarial drugs chloroquine (CQ) and primaquine (PQ) on the pharmacokinetics of a combined oral contraceptive (O.C.) have been studied in volunteers. Each woman was studied on 3 separate occasions over 3 cycles and plasma concentrations of ethinyloestradiol (EE2) and levonorgestrel were measured by radioimmunoassay following administration of a single dose of O.C. (30 micrograms EE2 + 150 micrograms levonorgestrel) in the absence and presence of the antimalarial drugs (PQ, 45 mg; CQ, 300 mg). Neither CQ or PQ given 1 h before the O.C. had any significant effect on plasma concentrations of EE2 or levonorgestrel or on any pharmacokinetic parameter determined. There is therefore, no evidence that CQ or PQ interfere with the hepatic handling of O.C.'s. This is in contrast to previously reported inhibitory effects of PQ on the metabolism of antipyrine.