Absorption and bioavailability of nebulized morphine.

During anaesthesia seven patients received a bolus of morphine 10 mg injected into the nebulization reservoir placed between the tracheal tube and the anaesthetic circle (IH). Five days after operation the same seven patients received morphine 10 mg i.m. On both occasions, venous blood samples were taken before and every 15 min after administration over 4.5 h for measurement of free morphine immunoreactivity by radioimmunoassay. There was marked individual variation in the serum morphine concentrations produced following each route of administration. The maximum serum morphine concentration following inhaled morphine was approx. six times lower than that after morphine i.m. and the time of occurrence differed significantly (P less than 0.001). The individual relative bioavailabilities of inhaled morphine varied from 9% to 35%, with a mean of 17%.