Naltrexone and Its Noroxymorphone Minor Metabolite - A Case Report

Opioid-positive urine drug screen during treatment with oral naltrexone and the clinical implications

Introduction

Naltrexone is an opioid antagonist that is FDA approved to treat alcohol dependence and opioid dependence. It is available as an oral tablet and an extended-release injectable suspension. Naltrexone is metabolized to the primary metabolite, 6-β-naltrexol, and to 2 minor metabolites, 2-hydroxy-3-methoxy-6-β-naltrexol and 2-hydroxy-3-methyl-naltrexone. One of the lesser-known metabolites of naltrexone is noroxymorphone.

Methods

A 27-year-old man taking oral naltrexone seen in the outpatient setting for alcohol use disorder and cannabis use disorder was found to have multiple positive urine drug screens (UDSs) for oxycodone. Confirmatory urine drug testing was completed and noroxymorphone was detected. A naloxone challenge test was conducted with negative results and the patient tolerated the transition from oral naltrexone to the extended-release injectable suspension of naltrexone.

Results

This case illustrates that it is possible for a patient stabilized on oral naltrexone to have a false-positive oxycodone UDS. Confirmatory urine drug testing was used to substantiate that the metabolite of naltrexone, noroxymorphone, was the cause of the false-positive oxycodone UDS.

Conclusions

One of the lesser-known metabolites of naltrexone, noroxymorphone, can cause a positive oxycodone UDS during treatment with oral naltrexone. Confirmatory urine drug testing should be conducted to confirm the presence of noroxymorphone and rule out alternative opioids.