Effect of butorphanol and morphine on pulmonary mechanics, arterial blood pressure and venous plasma histamine in the anesthetized dog.

Butorphanol, levo-N-cyclobutylmethyl-3, 14beta-dihydroxy-morphinan, is a new agonist-antagonist type analgetic agent which is 4 times more potent than morphine in experimental animals. Equianalgetic doses of butorphanol and morphine were compared, following rapid intravenous injection to anesthetized dogs, for their effects on pulmonary resistance, dynamic compliance, arterial blood pressure and venous plasma histamine levels. Butorphanol, 0.75 mg/kg, had no effect on pulmonary resistance, dynamic compliance or venous plasma histamine levels. Morphine, 3 mg/kg, increased pulmonary resistance, decreased dynamic compliance and elevated venous plasma histamine levels. Both drugs decreased arterial blood pressure but the hypotensive effect of butorphanol was significantly less in magnitude than that of morphine. Pretreatment with chlorpheniramine antagonized the effects of morphine on pulmonary resistance, dynamic compliance and arterial blood pressure. These results suggest that in man butorphanol may have less potential than morphine for causing airway constriction, hypotension and histamine release.