Assay and stability-indicating micellar electrokinetic chromatography method for the simultaneous determination of valacyclovir, acyclovir and their major impurity guanine in pharmaceutical formulations.

A micellar electrokinetic chromatography (MEKC) method for the simultaneous determination of the antiviral drugs acyclovir and valacyclovir and their major impurity, guanine, was developed. The influences of several factors (surfactant and buffer concentration, pH, applied voltage, capillary temperature and injection time) were studied. Using tyramine hydrochloride as internal standard, the analytes were all separated in about 4 min. The separation was carried out in reversed polarity mode at 28 degrees C, 25 kV and using hydrodynamic injection (15 s). The separation was effected in a fused-silica capillary 100 microm x 56 cm and a background electrolyte of 20 mM citric acid-1 M Tris solution (pH 2.75), containing 125 mM sodium dodecyl sulphate and detection at 254 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 0.1-1 microg/mL (guanine) and from 0.1 to 120 microg/mL for both valacyclovir and acyclovir. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 5.0%. The proposed method was successfully applied to the determination of the analytes in tablets and creams. From the previous study it is concluded that the stability-indicating method developed for acyclovir and valacyclovir can be used for analysis of the drug in various stability samples.