(HealthDay News) — Although initiation of extended-release naltrexone (XR-NTX) may be more difficult, XR-NTX and sublingual buprenorphine-naloxone (BUP-NX) are equally safe and effective once initiated for opioid relapse prevention, according to a study published online Nov. 14 in The Lancet.

Joshua D. Lee, M.D., from the New York University School of Medicine in New York City, and colleagues randomized 570 opioid-dependent adults to XR-NTX (administered as monthly intramuscular injections; 283 patients) or BUP-NX (daily self-administered sublingual film; 287 patients) to examine the differences in opioid relapse-free survival. 

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A significant induction hurdle was seen for XR-NTX, with fewer participants successfully initiating XR-NTX versus BUP-NX (72.1 versus 94.1 percent). The researchers found that in the intent-to-treat (ITT) population, the 24-week relapse rates were greater for XR-NTX than for BUP-NX (65.4 versus 56.8 percent; hazard ratio, 1.36; 95 percent confidence interval, 1.1 to 1.68); most of the difference was due to early relapse, seen in 88.6 percent of XR-NTX induction failures. Among the treated population, the 24-week relapse rates were similar (52 versus 55.6 percent for XR-NTX and BUP-NX, respectively; hazard ratio, 0.92; 95 percent confidence interval, 0.71 to 1.18). In the ITT population, opioid-negative urine samples and opioid-abstinent days significantly favored BUP-NX, while they slightly favored XR-NTX in the as-treated population.

“In this population it is more difficult to initiate patients to XR-NTX than BUP-NX, and this negatively affected overall relapse,” the authors write. “Once initiated, both medications were equally safe and effective relapse prevention. Methods to improve XR-NTX induction are needed.”

Several authors disclosed financial ties to the pharmaceutical industry.

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