Interactions between morphine and doxapram in the rabbit and mouse.

Certain actions of doxapram, administered alone and in combination with morphine, have been examined in the rabbit and the mouse. Single doses of doxapram were capable of stimulating respiration in both species. There was an increase in tidal volume in the rabbit and an increase in respiratory rate in the mouse. In both species the duration of action of single doses of doxapram was less than 15 min. In morphine-treated rabbits and mice single doses of doxapram affected neither the time course nor the intensity of the respiratory depression. In the rabbit repeated doses of doxapram did not produce tachyphylaxis with respect to the effect on tidal and minute volumes, and effectively reversed the respiratory depressant actions of morphine. The usefulness of this action must be balanced against the enhanced toxicity of doxapram observed in morphine-treated mice.