Simultaneous determination of terbinafine (Lamisil) and five metabolites in human plasma and urine by high-performance liquid chromatography using on-line solid-phase extraction

The antimycotic agent terbinafine (Lamisil) and five of its main metabolites were determined simultaneously in human plasma and urine samples by an isocratic HPLC method. The compounds were separated on a phenyl column following on-line solid-phase sample clean-up with a column-switching device. Terbinafine and its metabolites were detected by monitoring the column effluent with UV light at a wavelength of 224 nm. The linear range in plasma was assessed between 0 and 2500 ng/ml for the parent drug and metabolites V, IV and I. The linear response of metabolites III and II was assessed between 0 and 1250 ng/ml. In urine, linearity was assessed between 0 and 10,000 ng/ml for metabolites V, IV, III, II and between 0 and 1000 ng/ml for the parent drug and metabolite I. Quantification limits based on a C.V. < or = 20% and a bias < or = +/- 20% ranged from 20 to 500 ng/ml depending on the compound and the matrix. Inter-day and intra-day variations were similar indicating the ruggedness of the two methods. Due to the considerable differences in hydrophobicity between the compounds, extraction efficiencies ranged from 55 to 100%. Both methods were found to be reproducible and sufficiently sensitive for the evaluation of metabolite pharmacokinetics.