Concomitant Drug Interactions and Adverse Events With Methylnaltrexone


An expert in emergency medicine comments on the adverse event profile and concomitant use considerations with the administration of methylnaltrexone in patients suffering from opioid-induced constipation.

William F. Peacock, MD: The complications with any drug are other systemic problems like renal failure or liver failure. Like most drugs, methylnaltrexone had severe manifestations of 1 of those and has to have a limitation of the dose. For mild renal failure or mild liver failure, there’s no implication to dose reduce there. You can use standard dosing. There are drugs that have questionable adverse effects that are worsened with methylnaltrexone. There are very few, and for the most part they’re antibody-based drugs. For emergency physicians, none of the drugs we normally use do you have to worry about.

It’s an important point that the population we evaluated was pretty sick: 70% of patients were on an opioid because they had cancer and the full play of cancer therapies. That’s 1 of the strengths of this trial. We showed 2 things. First, there were no complications from their cancer therapy, and the drug still worked. The other important 1—and it’s relevant to emergency physicians—is the concern that the mechanism of the relief of the opioid-induced constipation might decrease their efficacy of pain relief. They’re taking an opioid because they have cancer pain, which is brutal pain. Bone metastases from cancer are awful, so they’re on a narcotic for that. You wouldn’t want to give them a drug that made their pain worse. If it turned off the opioid effect, the pain effect, this wouldn’t be a drug to use.

We found that the majority of these patients had no change in their pain. They got the opioid antagonist, but it works only on the colon. It doesn’t get to the μ-receptors in the brain. It can’t cross the blood-brain barrier, so they maintain their pain relief. They’re perfectly fine. They have the same pain control they started with, and it fixes the complication from that pain control. It’s a unique drug that way.

Transcript Edited for Clarity

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