(423) Evaluation of Methylnaltrexone and Enteral Naloxone for Opioid-Induced Constipation

Introduction: Opioid-induced constipation (OIC) is a common and distressing adverse effect of opioid-use in patients receiving opioids to manage pain or continuous infusion for sedation. The American Gastroenterological Association has published guideline recommendations describing proper medical management of OIC which recommends agents like methylnaltrexone (MNTX) for laxative-refractory OIC. Enteral naloxone (EN) is an agent which in multiple small, retrospective case studies has demonstrated similar efficacy in relieving OIC while also offering a potential cost savings. The purpose of this medication use evaluation was to compare the efficacy of MNTX versus EN in the treatment of OIC.

Methods: This was a retrospective analysis of patients treated with at least one dose of MNTX or EN between January 2016 and July 2022 across the University of Cincinnati Health System. Data collection was completed 24-hours prior to and the 48-hours following administration of MNTX or EN. Data points included administration of a maintenance bowel regimen (BR), other prokinetic agents, enteral access at time of the dose, and all opioids received in the proceeding 24 hours were converted to morphine milligram equivalents (MME). Treatment success was defined as a documented bowel movement (BM) with 24 hours of administration. Patients were matched in a 2:1 ratio of MNTX: EN in reverse chronological order for analysis.

Results: A total of 72 unique administrations of MNTX and 36 of EN were included for analysis. The majority of administrations of MNTX were in patients admitted to the floor and EN was given to a majority of patients in the emergency department (ED). Patients who received MNTX had higher MME (92.5 mg [IQR 33.3,303.8] vs 0 mg [IQR 0,15]) and were more like to be on a BR (61 [84.7%] vs 18 [50%]) than those who received EN. The median dose of MTNX administered was 12 mg and 4 mg for EN. Twenty-four hours post-administration 56 patients (77.8%) of patients who received MNTX and 19 patients (52.8%) who received EN had a documented bowel movement. Of the 30 patients who received EN in the ED, 100% of these patients were discharged after administration of EN.

Conclusions: EN represents a reasonable alternative agent when compared to MNTX in patients with enteral access for the treatment of OIC.