High-performance liquid chromatographic assay for the simultaneous monitoring of mefloquine and its acid metabolite in biological samples using protein precipitation and ion-pair extraction.

A high-performance liquid chromatographic (HPLC) method is presented for the simultaneous determination of mefloquine and its acid metabolite in plasma and whole blood. Plasma and whole blood are deproteinized with a combination of zinc and acetonitrile before extraction. Mefloquine and its acid metabolite are extracted simultaneously at pH 4 by methyl tert.-butyl ether, where mefloquine is extracted as an ion pair with heptanesulphonate. After evaporation of the organic phase, the residue is dissolved in mobile phase and injected on to the chromatographic column. A reversed-phase column (Spherisorb ODS-1) is used with acetonitrile-phosphate buffer (0.1 mol/l, pH 2.5) (42:58) containing 40 mmol/l perchlorate as the mobile phase. N,N-Dioctylamine was added to the mobile phase to give a concentration of 0.1% and the pH was adjusted to 2.3-2.7 with concentrated phosphoric acid. The method permits the determination of 0.10 mumol/l (30 ng/ml) mefloquine and its acid metabolite in plasma. The coefficient of variation was 5-6% at the therapeutic level (mefloquine 1-4 mumol/l, its carboxylic metabolite 2-6 mumol/l) in 0.5-ml samples. An alternative method is also described with a similar clean-up procedure that uses protein precipitation with zinc-acetonitrile as a sample pretreatment for therapeutic monitoring of mefloquine and metabolite in plasma and whole blood. Using this method, 0.25 mumol/l mefloquine and its metabolite can be determined. The results from the two methods correlate well.