Quantitation of trihexyphenidyl from plasma using a mass-selective detector and electron-impact ionization

A method is described for the measurement of plasma concentrations of trihexyphenidyl, an anti-parkinsonian drug. The drug was extracted from human plasma samples. Then, gas chromatography-mass spectrometry with electron-impact ionization and selected-ion monitoring allowed the specific quantitation of trihexyphenidyl, with bupivacaine used as an internal standard. Linear calibration curves were obtained in the concentration range 5-100 ng/ml. Precision and accuracy were found acceptable for quantitation during pharmacokinetic trials of the drug. This method has been successfully applied to bioavailability studies after Parkinane and Artane administration to humans.