Determination of nalbuphine in drug abusers' urine

Nalbuphine, chemically derived from the oxymorphone, is a potent analgesic with narcotic antagonist activity. Because of the limited availability of methamphetamine, the abuse of nalbuphine as an alternative for methamphetamine began in late 1991 in Korea. In this study, the analysis of nalbuphine by gas chromatography (GC) was investigated. Using solid-phase extraction, we analyzed drug abusers' urine samples in order to quantitate nalbuphine by GC after trimethylsilyl derivatization with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), trimethylsilylimidazole (TSIM), and 1% trimethylchlorosilane (TMCS) (100:2:5). Nalbuphine and its two metabolites, nornalbuphine and 6-ketonalbuphine, were identified by gas chromatography-mass spectrometry. The ratio of total (i.e., nonconjugated and glucuronide) nalbuphine to nonconjugated nalbuphine ranged from 1.8 to 3.0 in the five drug abusers' urine. The urinary excretion of nalbuphine showed that 93% of nalbuphine was excreted in 6 h after intraperitoneal administration of 10 mg/kg nalbuphine to five rats. No nalbuphine was detected in the urine specimens of rats from 24 to 48 h.