Pain gain

2017 Spring

A commercially available drug approved to treat opioid-​induced constipation may also block two of the most problematic side effects of opioids: a growing tolerance to them and a paradoxical increased sensitivity to pain. Patients with these side effects may require ever-larger doses, raising their risks of addiction and of respiratory failure.

School of Medicine researchers led by assistant professor of anesthesiology, perioperative and pain medicine and of neurosurgery Gregory Scherrer, PhD, PharmD, first demonstrated in mice that knocking out the opioid receptors in the pain neurons outside the brain and spinal cord — leaving those in the central nervous system intact — allowed the mice to receive long-lasting pain relief from morphine without the two detrimental side effects.

They then administered the constipation drug methyl­naltrexone bromide, which blocks the opioid receptors in the mice’s peripheral pain neurons but not those in the central nervous system, with similarly successful results.

Scherrer is the senior author of the study, published in the February 2017 issue of Nature Medicine.