High-performance liquid chromatographic method for the quantitation of flecainide, a new antiarrhythmic, in human plasma and urine.

A simple, selective, sensitive, and accurate high-performance liquid chromatographic method for the quantitation of flecainide in human plasma and urine is described. The method is based on initially washing the sample with hexane followed by a single extraction with hexane. The extracted drug and internal standard are chromatographed on a Zorbax TMS column with a mobile phase consisting of acetonitrile-1% acetic acid in 0.01 M pentanesulfonate (45:55, v/v). The eluent is monitored at 308 nm. This method can routinely quantitate plasma or urine flecainide concentrations as low as 22 ng/ml with a 1-ml sample and 11 ng/ml with a 2-ml sample with no interference from endogenous substances and many drugs and their metabolites. The standard curve is linear over a concentration range of 22-1746 ng/ml. The precision and accuracy of the described method are suitable for monitoring flecainide levels in therapeutic, tolerance, and pharmacokinetic studies in humans.