Intravenous Morphine Can Avoid Distressing Constipation Associated With Oral Morphine: A Retrospective Analysis of Our Experience in 11 Patients in the Palliative Care In-Patient Unit

Abstract

Morphine is the preferred strong opioid analgesic. Most of the adverse effects, such as daytime drowsiness, dizziness, mental clouding, and effects on cognitive and psychomotor function or nausea and vomiting, usually resolve with time. The main continuing adverse effect of morphine is constipation, and prophylactic use of laxative is almost always required. We are presenting retrospective data of 11 patients admitted in our palliative care unit over the past 5 months for new (not yet received any opioid analgesic in any form) and severe cancer pain management. It was found that none of the patients was having constipation with intravenous morphine. This finding can be explained on the basis of differences in pharmacologic profiles, in affinity to opioid receptor, and a higher exposure of opioid-binding receptor in the GI tract after oral administration of morphine compared with intravenous morphine. This explanation was further affirmed as constipation and need for laxative was reported by 7 of the 11 patients when they were given the equi-analgesic oral doses of morphine. Thus, the route of administration seems to be responsible for the above finding; hence, further evaluation with prospective observation and data collection is being planned to look for external validity in a larger population catered by our palliative care unit.