Cyclaradine is a novel carbocyclic nucleoside with good activity against the viruses of the herpes group. To facilitate pharmacokinetic studies on cyclaradine, an automated column-switching high-performance liquid chromatographic (HPLC) method was developed for the determination of cyclaradine in serum. Deproteinized serum containing cyclaradine was directed to an on-line extraction column which retained cyclaradine while many potentially interfering components were eluted to waste. Fourteen minutes later, the switching valve was automatically rotated, permitting an appropriate mobile phase to elute cyclaradine from the extraction column onto an analytical C18 column for further separation and UV detection. The method showed excellent linearity (r = 0.9995) for cyclaradine concentrations ranging from 0.05 to 5 micrograms/ml. It also provided good sensitivity (0.05 micrograms/ml). The assay was precise, with within-run and between-run coefficients of variation of less than 1.90%. The accuracy, expressed as differences between observed values and theoretical values, ranged from -4.12 to 4.80%. The assay involves a simple deproteinization of serum followed by a fully automated sample cleanup, eliminating long and tedious manual extraction prior to HPLC. The column-switching HPLC method has been successfully used for the determination of cyclaradine serum levels in squirrel monkeys following a single oral dose of 20 mg/kg.
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