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Methyl-naltrexone (Relistor®), a peripheral μ-opioid receptor antagonist shown to induce laxation in patients receiving opioids, is licenced for use in palliative care; a similar benefit is proposed in critical care patients. Impaired gut motility and constipation are common issues in the critical care setting with contributing factors including trauma, surgery and use of opiate analgesics. The effects of methyl-naltrexone were studied on seven patients in whom conventional treatment for constipation with stimulant and osmotic laxatives, faecal softeners and suppositories failed to produce effects.
Over a 6-week period, 15 critically ill patients with opiate-induced constipation (OIC) of more than 4 days duration were prospectively studied. All patients were treated with conventional methods from admission to critical care, which included regular senna and sodium docusate, supplemented with glycerin suppositories and picolax for resistant constipation. Methyl-naltrexone was administered to seven patients at 0.15 μg/kg subcutaneously on alternate days until laxation occurred. The remainder of patients in the study continued with conventional therapy.
Six out of seven patients responded to methyl-naltrexone with laxation occurring between 12 and 24 hours. One patient did not respond due to faecal impaction but subsequently experienced laxation after manual disimpaction. Side effects were few (nausea 14%, vomiting 14%) and there was no increase in opiate requirement. Those patients treated by conventional means eventually produced laxation after a further 3 to 5 days.
Previous studies have shown the earlier return of gut motility improves patient progress, facilitates earlier respiratory weaning, prevents debilitation and results in reduced length of stay. Methyl-naltrexone is a safe and efficacious drug for the treatment of OIC in critical care patients in whom conventional treatments prove unsuccessful. Side effects are few and opiate requirements remain unchanged. Further investigation to elucidate the cost-effectiveness of methyl-naltrexone use in OIC of the critically ill patient is warranted.