A gas chromatography-mass spectrometric method was employed for the determination of the antispasmodic drug, eperisone, in plasma. Excellent sensitivity was achieved by the selection of the base ion peak at m/z 98 of eperisone and a suitable internal standard, tolperisone, and by using a cyanopropylphenyl-bonded fused-silica capillary column. The lower limit of sensitivity was 10 pg/ml with a signal-to-noise ratio of 3. Another internal standard, decadeuterium labelled eperisone, was inferior to tolperisone in terms of accuracy and reproducibility at low levels of eperisone. The present method allows the determination of eperisone in human plasma after an oral administration of eperisone hydrochloride.
