Specific, sensitive and accurate LC-MS/MS method for the measurement of levovirin in rat and monkey plasma

Levovirin is a guanosine nucleoside analogue and the L-enantiomer of ribavirin. Levovirin has a better safety profile than ribavirin, exerts similar immunomodulatory effects in a mouse efficacy model, and may provide a better therapeutic option than ribavirin in patients with chronic hepatitis C virus (HCV) infection. To facilitate pharmacokinetic studies, a LC-MS/MS method for the analysis of levovirin in rat and monkey plasma was developed and validated. The method involved adding ICN 10537 as an internal standard, protein precipitation with acetonitrile followed by separation on an Intersil Silica column, and quantification by a MS/MS system equipped with positive electrospray ionization (ESI) in the multiple reaction monitoring (MRM) mode. The MS/MS reaction was selected to monitor the 245-->113 and 259-->128 transitions for levovirin and internal standard, respectively. The calibration curve was linear over a concentration range of 10-5000 ng/ml. The limit of quantitation was 10 ng/ml, the coefficient of variation (CV) was 3-5%, and the bias was 3-6%. Intra- and inter-day analysis of QC samples at 30, 1500 and 3500 ng/ml indicated that the method was precise (CV<6%) and accurate (bias <9%). Levovirin in rat and monkey plasma was stable at 5 degrees C for at least 24 h, 0 degrees C for at least 4 h, and after three freeze-thaw cycles. This specific, accurate and precise assay is useful in the study the pharmacokinetic characteristics of this compound.