Determination of ibudilast in human serum by high-performance liquid chromatography for pharmacokinetic study

A simple, accurate, precise and cost effective reversed-phase HPLC method was developed to determine the concentration of ibudilast in human serum. Ibudilast and an internal standard, butyl 4-hydroxybenzoate, were extracted by liquid-liquid extraction with methyl tert-butyl ether. HPLC analysis was carried out under the following conditions: a Luna C(18)(2) 5 microm column, a mobile phase of acetonitrile-0.02% phosphoric acid (50 : 50, v/v, adjusted to pH 6.0 with triethylamine) and a UV detector at 319 nm. The chromatograms showed good resolution and sensitivity as well as no interference from the human serum. The calibration curves were linear over the concentration range, 1-100 ng/mL, for serum with correlation coefficients >0.999. The intra- and inter-day assay precision as well as the accuracy fulfilled the international requirements. The mean absolute recovery for human serum was 101.7 +/- 6.1%. The lower limit of quantitation in human serum was 1 ng/mL, which is sensitive enough for pharmacokinetic studies. Stability studies revealed that ibudilast in human serum was stable during storage as well as during the assay procedure. This method was applied successfully to an examination of the pharmacokinetics of ibudilast in human subjects following a single oral dose of an ibudilast (10 mg) capsule.