Mefloquine effect on disposition of halofantrine in the isolated perfused rat liver.

Halofantrine and mefloquine are antimalarial drugs used in the treatment of malaria, including that caused by chloroquine-resistant Plasmodium falciparum. Reports of drug-associated adverse reactions, including sudden death in one patient, have prompted concerns over the safety of halofantrine and the potential for drug-drug interactions. We used the isolated perfused rat liver (IPRL) model to investigate a possible hepatic metabolic or pharmacokinetic drug-drug interaction between halofantrine and mefloquine. Pharmacokinetic parameter estimates for halofantrine in the IPRL reflected the pattern seen in in-vivo studies with doses comparable with clinical doses. Halofantrine parameter estimates (mean +/- s.d.) were: volume of distribution (Vd), 7.53 +/- 1.45 mL (g liver)-1; clearance (CL), 0.11 +/- 0.07 mL min-1 (g liver)-1; initial distribution half-life (initial t1/2), 14.62 +/- 2.38 min; terminal half-life (terminal t1/2), 138.7 +/- 178.8 min; AUC 606 +/- 194 mg mL-1 min-1 (g liver)-1; elimination rate constant (Ke), 0.0135 +/- 0.012 min-1. Prior dosing with mefloquine did not affect halofantrine perfusate pharmacokinetic parameter estimates of Vd, Ke, initial and terminal t1/2 (P > 0.05). A single dose, short term (4-6 h) interaction showed significant changes in the perfusate clearance of halofantrine in mefloquine-pretreated livers using higher doses of halofantrine. Substantial changes were seen in bile production (P < 0.05) and biliary clearance (P < 0.05) of halofantrine in mefloquine-pretreated livers. These findings may have clinical implications in models utilizing multiple drug dosages or in patients with severe malaria who have disease-related cholestasis.