Simple and rapid reversed-phase high-performance liquid chromatographic determination of baclofen in human plasma with ultraviolet detection. Application to a pharmacokinetic study.

A sensitive, selective, and rapid reversed-phase high-performance liquid chromatographic method for separation and quantitation of intact racemic baclofen in human plasma has been described. Baclofen is very soluble in water and cannot be extracted efficiently by an organic solvent. Therefore, baclofen was isolated from plasma endogenous materials by adding 0.50 ml of acetonitrile and 50 mg of zinc sulfate to 1.0 ml of plasma. A 15 cm X 4.6 mm, 10-microns octyl (C8) column was slurry packed and used throughout the study. An isocratic mobile phase containing 0.01 M monobasic potassium phosphate (pH congruent to 3.5)-acetonitrile (80:20, v/v) was delivered at a flow-rate of 1.0 ml/min through the chromatographic system. Baclofen was detected with an ultraviolet-visible variable-wavelength detector at 220 nm and 0.50-0.005 a.u.f.s. The time needed to complete the analysis of one sample was approximately 15 min. The limit of detection for the assay of racemic baclofen was 35 ng/ml. After an oral dose of 20 mg of baclofen, blood samples were collected at several time points and plasma was analyzed using the method developed in this study. Various pharmacokinetics parameters were determined from the plasma concentration versus time profile of baclofen.