Liquid chromatography-tandem mass spectrometry determination of baclofen in various biological samples and application to a pharmacokinetic study.

Baclofen is a structural analogue of γ-aminobutyric acid (GABA) that has been used for the treatment of spasticity since 1977. This study describes a simple and sensitive LC/MS/MS assay for the quantification of baclofen in rat plasma, urine, as well as various tissue samples. The assay utilized a simple protein precipitation and achieved lower limit of quantification (LLOQ) of 0.25ng/mL for rat plasma and brain samples and 2ng/mL for rat urine, liver and kidney samples. The assay was validated to demonstrate the specificity, linearity, recovery, LLOQ, accuracy, precision, and stability by using matrix matched quality control samples. There is no endogenous or exogenous peaks interfering with the analytes and matrix effects were minimized by optimized separation condition. The assay was linear over a concentration range of 0.25-500ng/mL for rat plasma and brain tissue, and 2-5000ng/mL for rat urine, kidney and liver with correlation coefficients >0.999. The mean intra- and inter-day assay accuracies were 94.6-104.6 and 96.0-103.6%, respectively. The mean intra- and inter-day precisions were 5.71 and 5.70%, respectively. The developed assay was successfully applied to a pharmacokinetic study and examined urinary excretion and tissue distribution of baclofen in rats following intravenous and oral administration.