Rectal administration of morphine hydrogel: absorption and bioavailability in women.

Seven patients undergoing radiological treatment for carcinoma of the uterus were given morphine intramuscularly (0.15 mg X kg-1) and morphine in a starch hydrogel rectally (0.56 mg X kg-1) on two separate occasions. The hydrogel preparation was used to order to improve the contact between the rectal mucosa and thus improve and possibly prolong the absorption of morphine. Plasma concentrations of morphine were followed for 8 h and analysed with a GC/MS technique. It was found that 45-120 min after administration of morphine hydrogel, a mean maximum plasma morphine concentration of 61 ng X ml-1 was obtained. After 8 h, the mean plasma concentration was 10 ng X ml-1. The mean biological availability of morphine hydrogel was 48% (range 31-72%). It is suggested that morphine hydrogel, given rectally, can be clinically useful.