Comparative gastrointestinal and biliary tract effects of morphine and butorphanol (Stadol)

Butorphanol, levo-N-cyclobutylmethyl-3,14 beta-dihydroxy-morphinan, is a new agonist-antagonist type analgetic agent which is 4 to 8 times more potent than morphine in experimental animals and man. Butorphanol and morphine were evaluated in mice and dogs for their gastrointestinal and biliary tract smooth muscle effects. Morphine decreased the propulsion of a charcoal meal through the gastrointestinal tract of the mouse in a dose related manner with the maximal inhibition obtainable being 90%. Butorphanol produced a maximal inhibition of motility of only 40% with very high doses producing less of an inhibitory effect than lower doses. In dogs, morphine caused a dose-dependent increase in duodenal smooth muscle activity and a dose-dependent decrease in bile duct flow. A clinically effective i.v. dose of morphine (0.1 mg/kg) produced a statistically significant spasmogenic effect on dog biliary tract and gastrointestinal smooth muscle, while a clinically effective equianalgetic i.v. dose of butorphanol (0.025 mg/kg i.v.) had little or not effect on the biliary or gastrointestinal systems. These findings indicate that at equianalgetic doses, butorphanol should produce less constipation and less biliary tract and gastrointestinal smooth muscle spasm than morphine.