Morphine for postoperative analgesia. A comparison of intramuscular and subcutaneous routes of administration.

Intermittent parenteral bolus doses of morphine are commonly used for postoperative analgesia. Morphine is typically given by intramuscular or intravenous injection but there are theoretical advantages for the subcutaneous route of administration. Fifty-nine patients entered a prospective randomized double-blind cross-over study comparing intermittent intramuscular and subcutaneous morphine boluses. Patients received 0.15 mg/kg of morphine by subcutaneous or intramuscular injection. They were reviewed at the time of injection, after 15 minutes and each hour for four hours. The majority of patients indicated a strong preference for the subcutaneous route. There were no significant differences in pain scores, respiratory rate, arterial oxygen saturation, heart rate, mean arterial pressure, sedation or nausea scores between intramuscular and subcutaneous administration of morphine. Postoperative analgesia by subcutaneous morphine bolus injection is as effective as intramuscular injection with a similar side-effect profile but with greater patient acceptance and less risk.