Quantitative determination of nalbuphine in plasma using electron-capture detection.

A procedure for the determination of nalbuphine in plasma is presented. The compound and an internal standard are extracted into benzene-2-propanol from plasma at pH 10.4, followed by back-extraction into 0.1 N HCl. After the acid phase is washed with benzene and the compound is reextracted into benzene-2-propanol, the heptafluorobutyryl derivatives are formed and determined using electron-capture GLC. The lower limit of sensitivity is approximately 0.5 ng/ml, and the upper limit of the linear dynamic range is greater than 50 ng/ml. Peak plasma levels of 50 and 150 ng were observed in two dogs 10 and 20 min, respectively, after subcutaneous administration of 1 mg of nalbuphine/kg. Nalbuphine was detectable in plasma 5 hr after administration.