A dose-response study with nalbuphine hydrochloride for pain in patients after upper abdominal surgery

Six male patients were studied on the morning following upper abdominal surgery for highly selective vagotomy. Nalbuphine hydrochloride was infused i.v. at different rates that increased progressively in each hour over a 4-h period. In the last 15 min of each hour, the plasma nalbuphine concentrations were almost steady (73-68, 71-82, 116-113 and 201-208 ng ml-1). Patients and an observer made hourly assessments of pain and sedation. Although the changes in the pain and sedation scores were not significant, the patients' mean pain scores increased when the mean plasma nalbuphine concentrations were greater (greater than 82 ng ml-1), which suggested that nalbuphine analgesia had been reversed. Nalbuphine caused sedation and possibly induced amnesia which could invalidate retrospective assessment, since the patients' assessment of analgesic efficacy at the end of the study was good. No cardiovascular depression or significant decrease in the ventilatory rate was recorded.