Opioid overdose deaths can occur in patients with naltrexone implants

To the Editor: I read with interest the article by Gibson and colleagues,1 who purport to have evaluated the claim that naltrexone “prevent[s] relapse to opioid use and therefore fatal opioid overdose”. The article fails in its stated intent, as it neglects to provide adequate context and comparison in its evaluation of the five deaths between 2000 and 2004 identified through Australia’s National Coroners Information System. The significance of the data cannot be assessed, as the authors omitted the number of naltrexone implants made available through the Therapeutic Goods Administration Special Access Scheme and comparison with other opioid users. This is extraordinary, given the high risk of death in this group both in and out of treatment.2

Of the five cases identified, three people no longer had active naltrexone implants and therefore could not be used to support the title “Opioid overdose deaths can occur in patients with naltrexone implants” any more than recurrence of depression can be attributed to previous antidepressant treatment. The remaining two deaths involved polydrug use, a known risk factor in overdoses;3 naltrexone did not prevent death, but no clear causation was established.

In summary, this article was about two deaths among an unspecified number of naltrexone implant users across Australia over a period of 4–5 years, and it overlooked comparison with other opioid users, including those in the accepted gold-standard treatment, methadone maintenance. From the data presented, it is impossible to determine if the implant was associated with an increased or decreased risk of fatal overdose. A previously raised valid concern is the risk of overdose following all abstinence-based treatments.4 Post-treatment outcomes from randomised controlled trials with naltrexone implants are needed to quantify this risk.

Despite the inadequacies described above, this article was published in a prestigious Australian medical journal, with a title linking opioid overdose with naltrexone, yet lacking the scientific basis for this association. Medical practitioners have limited time, frequently scan titles and abstracts, and rely on editors to provide summarised information based on scientific rigour.5 Perhaps a more accurate title would have been “Two cases with naltrexone implants among X number of opioid-related deaths between 2000 and 2004”.