Stereoselective halofantrine and desbutylhalofantrine disposition in the rat: cardiac and plasma concentrations and plasma protein binding.

Halofantrine (HF) is a chiral antimalarial drug known to cause cardiac arrhythmias in susceptible patients. In this study, the cardiac uptake and plasma protein binding of HF and desbutylhalofantrine (DHF) enantiomers were examined in the rat. Rats were given 2 mg/kg of either HF HCl or DHF HCl intravenously, then sacrificed at various times after dosing. Specimens were assayed using stereospecific methods. Uptake of HF and DHF enantiomers into heart was rapid. Substantial concentrations of both HF and DHF enantiomers were observed in rat heart, with stereoselectivity being noted for both in plasma and heart. Stereoselectivity was more pronounced for HF (AUC (+):(-) ratio= 1.58) than DHF (AUC (+):(-) ratio =1.16) in heart tissue. Heart:plasma AUC ratios of 6.8-8.0, and 9.3-21, were observed for HF and DHF enantiomers, respectively, indicating that DHF has greater cardiac uptake than HF itself. Plasma protein binding was extensive for both HF and DHF (>99.95%), and was stereoselective for DHF, with a 38% higher unbound fraction for (-)-DHF than antipode. In contrast, binding of HF enantiomers was non-stereoselective. The lower degree of stereoselectivity for DHF in heart tissues was attributable to its greater stereoselectivity in plasma protein binding.