Rapid determination of valaciclovir and acyclovir in human biological fluids by high-performance liquid chromatography using isocratic elution.

A rapid high-performance liquid chromatographic assay with isocratic elution is developed for the simultaneous quantification of valaciclovir (VACV) prodrug and its active converted compound, acyclovir (ACV), in biological fluids of treated patients. For serum, the samples are deproteinized with perchloric acid in presence of 1-methylguanosine as the internal standard (IS). For urine and dialysis liquid, the samples are diluted with a mobile phase containing the IS, then filtered. VACV, ACV and the IS are separated on a SymmetryShield RP-8 column with acetonitrile-ammonium phosphate buffer as the mobile phase and detected at 254 nm. The chromatographic time is about 12 min. The relative standard deviations (RSD) of VACV and ACV standards are between 0.5 and 3.5%. Most endogenous nucleosides and their metabolites, psychotropic drugs and drugs of abuse are shown not to interfere with this technique. The method has been applied to study the pharmacokinetics of VACV and ACV in serum, dialysis liquid and urine of renal failure patients on continuous ambulatory peritoneal dialysis (CAPD) under oral treatment of VACV.