Twenty-four, nonsmoking, healthy subjects (12 men, 12 women) between the ages of 18 and 41 years (mean, 28.6 years) and weighing 52-102 kg (mean, 70.3 kg) participated in this inpatient study. All ...

Initially, butorphanol was only available for parenteral administration because of significant first-pass hepatic metabolism and poor absolute bioavailability (5-17%) after oral administration.