Determinations of zidovudine/didanosine/nevirapine and zidovudine/didanosine/ritonavir in human serum by micellar electrokinetic chromatography

Micellar electrokinetic chromatography methods were developed and validated to separate and quantitate anti-HIV drug mixtures containing zidovudine(AZT)/didanosine(ddl)/nevirapine (mixture A) and AZT/ddl/ritonavir (mixture B) in human serum. Serum samples were prepared using a solid-phase extraction procedure. The effects of various factors such as buffer type, buffer and surfactant concentrations, and pH on the separations were investigated. The optimized resolution was achieved with a run buffer containing 18 mM sodium dodecylsulfate in 15 mM phosphate and borate buffer (pH 9.0). An uncoated 52 cm (effective length 30 cm) x 50 mum ID fused-silica capillary operated at 30 degreesC was used in the analysis with UV detection at 210 nm. Aprobarbital was chosen as the internal standard. All analytes were separated within 14 min with a voltage of + 15 kV and a current around 30 VA. The methods were validated over the range of 0.5-25.0 mug/ml for AZT, 0.8-18.5 mug/ml for ddl, 0.5-22.8 mug/ml for nevirapine in mixture A and the range of 0.5-25.0 mug/ml for AZT, 0.8-18.5 mug/ml for ddl, 1.2-28.8 mug/ml for ritonavir in mixture B. Intra-day and inter-day accuracy was less than 12.4% and intra-day and inter-day precision was less than 13.9% for both mixtures. Extraction recoveries of all analytes from serum were higher than 75.9%. The assay should be applicable to pharmacokinetic studies and routine monitoring of these drugs in serum. (C) 2002 Elsevier Science B.V. All rights reserved.