Improved assay method for the determination of pyronaridine in plasma and whole blood by high-performance liquid chromatography for application to clinical pharmacokinetic studies. 
An improved high-performance liquid chromatography method using a diisopropyl-C14 reversed-phase column (Zorbax Bonus-RP column) and a liquid-liquid extraction technique with UV detection is presented for the analysis of pyronaridine in human whole blood and plasma.  Tribasic phosphate buffer (50 mM, pH 10.3) and diethyl ether were used for liquid-liquid extraction.  The mobile phase consists of acetonitrile-0.08 M potassium dihydrogen phosphate buffer (13:87, v/v) with the pH 2.8 adjusted by orthophosphoric acid.  Amodiaquine was found to be a suitable internal standard for the method.  The quantification limit with UV detection at 275 nm was 3 ng on-column for both plasma and blood samples.  The method was applied to plasma and blood specimens from a rabbit after a single intramuscular dose of pyronaridine tetraphosphate (20 mg/kg as base).  From this in vivo study, evidence was found that pyronaridine is concentrated in blood cells, with a blood:plasma ratio ranging from 4.9 to 17.8.  We conclude that blood is the preferred matrix for clinical pharmacokinetic studies.