Effect of a new analgesic, MR 1268, on circulatory and respiratory indices in volunteers.

MR 1268, a benzmorphan derivative with marked morphine-like properties and weaker antagonist properties was administered to six healthy male volunteers who each received MR 1268 2.5,5,10 and 20 mg i.v. in random order. There were no significant changes in the cardiovascular indices measured. However, significant and dose-related decreases in expired minute volume were observed. With 20 mg, consistent increases in Paco2 coincided with maximum decrease in ventilation, indicating some degree of alveolar hypoventilation. Drowsiness was dose-related but of short duration and only significant with 20 mg. Pupillary size and reaction remained unaffected.