GLC determination of nanogram quantities of a new analgesic, nefopam, in human plasma

A sensitive and specific method was developed for the quantitative GLC determination of plasma nefopam levels. The method includes a multiple-step solvent extraction of the analgesic drug and the internal mass standard, orphenadrine. The accuracy, expressed as the relative error, was--4,6,6, and 4% at 20, 40, 70, and 130 ng/ml, respectively. The precision, expressed as relative standard deviation, was 17, 7, 3, and 5% at these same concentrations, respectively. Quantitation of nefopam in human plasma is possible down to 20 ng/ml with a 2-ml plasma sample; the sensitivity can be increased by using larger plasma samples. The methods was applied successfully to the determination of plasma nefopam levels in humans in pharmacokinetic studies at therapeutic doses.