Unplanned admissions to two Sydney public hospitals after naltrexone implants

In reply: Our case series1 aimed to alert health practitioners to the types of hospital presentations associated with naltrexone implants and issues in managing such patients, particularly as these have not been well documented in the medical literature. These letters appear critical of any such communication.

We maintain that our article1 identifies important clinical issues — such as the difficulties of providing analgesia in patients with implants of uncertain duration of effect (whereby the treating hospital staff have no way of knowing whether the implant is providing “active” plasma levels of naltrexone, given the lack of a licensed product). Ultimately, our study could not hope to provide the type of data that can only be accurately determined by independent clinical trials — such as the incidence rate of serious adverse events (as suggested by Little and Murray) or how these are most effectively managed (eg, the role of octreotide compared with ondansetron for managing protracted vomiting, as suggested by Kozminsky).

A key complaint from the correspondents is whether the serious adverse events of opiate withdrawal and dehydration were caused by the naltrexone implant or by the rapid opioid detoxification process that accompanied the implant’s insertion. We acknowledged the difficulty of attributing causality in our article, but, unlike the correspondents, we cannot dismiss the possibility that the naltrexone implant may have contributed to the severity or duration of the opiate withdrawal syndrome. Clearly, there is a pharmacological basis as to how the presence of naltrexone from an implant may contribute to opiate withdrawal in a recently detoxified individual. Research comparing rapid opioid detoxification plus a naltrexone implant with conventional detoxification plus a naltrexone implant is required, to allow an assessment of whether naltrexone implants themselves contribute to the incidence, severity or duration of any opiate withdrawal. Until such data exist, it is appropriate to associate opiate withdrawal with naltrexone from the implants.

We concur with several of the correspondents that further research is required to address many of the issues raised by our study, as well as better communication between service providers, better procedures for management of complications, and better assessment and patient selection. We maintain that naltrexone implants should not be routinely used until research has demonstrated their safety and efficacy, and, importantly, until there is a licensed naltrexone implant product with appropriate regulatory safeguards for patients and providers.