A study completed more than six years ago but published online just last week in the American Journal of Psychiatry documents higher treatment retention rates in opioid-dependent patients taking injectable naltrexone compared with those on the oral formulation of the drug. The 24-week study also found a lower percentage of opioid-positive urine tests in the injectable naltrexone group.
Study authors concluded in their paper that even with the strong behavioral support that patients in both treatment groups received during the study, the results demonstrate that “oral naltrexone is an inferior treatment and should be avoided clinically, other than perhaps for very select cases with a high likelihood of adherence.”
The study's lead author, Maria A. Sullivan, MD, PhD, worked full-time in the Department of Psychiatry at Columbia University when the study was designed and conducted and is now senior medical director of clinical research and development at Alkermes, maker of the injectable naltrexone formulation sold as Vivitrol.
The open-label study involved 60 adult participants who met DSM-IV criteria for current opioid dependence; among those excluded from participation were individuals dependent on alcohol and those taking psychotropic medication. After detoxification and induction on oral naltrexone, patients were randomized to oral naltrexone 50 mg a day or injections of naltrexone every four weeks. All patients also received behavioral counseling that emphasized medication adherence and offered cash voucher rewards for clinic session attendance.
The researchers found that 16 of 31 injectable naltrexone users (57.1%) remained in treatment at 24 weeks, compared with only 9 of 32 oral naltrexone users (28.1%). Also, injectable naltrexone users had a lower percentage of opioid-positive urine tests, and on average attended more therapy sessions over the course of the study than oral naltrexone users.
A total of 110 individuals had originally consented to participate in the study, but 50 could not complete naltrexone induction; the requirement to be opioid-free for a several-day period before starting on naltrexone has posed a challenge in comparison to induction to agonist medications for opioid dependence, such as methadone and buprenorphine.
However, the authors stated that this study's results for treatment retention suggest that the injectable formulation of naltrexone “may be a viable alternative to prevent relapse in patients seeking treatment for opioid use disorder who do not prefer an agonist approach.”