Morphine sulfate is a strong opioid that is often used to treat moderate to severe chronic pain in patients with cancer. Oral administration is preferred, and doses should be given at regular intervals around the clock to provide good pain control. The use of oral morphine provides effective pain control in most cancer patients with pain. When oral morphine is ineffective, the next option is parenteral morphine. The preferred route is intravenous because it provides good analgesic effect and can be titrated quickly. Most studies about this route were small or short-term. Glare and associates studied the effectiveness of continuous intravenous morphine in the pain management of patients with advanced cancer. They also studied the adverse effects of this pain-management strategy.
The study was a retrospective review of cancer patients who were managed in a palliative care program and had moderate to severe pain. Data collected included information about pain mechanism, preinfusion opioid choice and dosage, other medications used, indication for parenteral morphine infusion, and information about adverse effects. Demographic data and information about primary and secondary cancer sites also were collected. Pain control was rated as good, partial, poor, or uncertain, based on the assessment of the palliative care team.
The most common indication for continuous infusion of morphine was to relieve uncontrolled pain. Pain control was considered good in 69 percent of the patients, partial in 23 percent, and poor in 6 percent. The two main reasons for discontinuing intravenous morphine were patient death or a switch back to oral morphine.
Forty-eight percent of the patients reported having no side effects. The most common side effect was constipation, followed by sedation and confusion (see the accompanying table). Five percent of patients had respiratory depression, most often resolving with a morphine dosage reduction. Only 26 patients had side effects that were serious enough to require a dosage reduction. The authors also noted that the conversion to oral morphine was consistent with information from previous publications suggesting that the conversion ratio should be 3:1, oral to parenteral.
The authors conclude that continuous-infusion intravenous morphine sulfate provides safe and effective pain management in cancer patients with moderate to severe pain. Dose-limiting side effects are unusual, and many patients with side effects respond favorably to dosage reduction.