By Dr. Janice Mann

When it comes to treating opioid addiction, preventing the severe symptoms of withdrawal – including drug cravings, anxiety, restlessness, diarrhea, sweating, and rapid heartbeat, is one of the keys to preventing relapse. That’s where opioids like methadone and buprenorphine are helpful. While they act on the same receptors in the body as opioids like morphine and heroin to prevent withdrawal symptoms, they don’t lead to the “high” or sense of euphoria experienced with opioids we associate with addiction.

But there is a whole other type of medication that might also be helpful when treating people with opioid addiction. A drug called naltrexone actually blocks the opioid receptors in the body, blocking the effects of any opioids that are taken. This drug can’t be used immediately in someone currently taking opioids, as it would cause very severe withdrawal symptoms. But once a person has successfully stopped taking other opioids with the help of methadone or buprenorphine, naltrexone could potentially be the next step in helping to prevent a relapse. Naltrexone is also used in the treatment of alcohol dependence.

Until recently, naltrexone was available only in a formulation to be taken by mouth, and had to be taken at least twice a week, if not every day. This made it difficult for some patients with opioid use disorder or addiction to stick to their treatment. And without taking their naltrexone, these patients could feel the high or euphoria again from any opioids taken and potentially experience a relapse. However, now an injectable form of naltrexone exists, which is injected into the muscle only once a month. This extended-release form of naltrexone, which is significantly more costly than the oral formulation, is known by the brand name Vivitrol. Currently in Canada, this injectable, extended-release form of naltrexone is available only through Health Canada’s Special Access Programme, and most recently, through a new Health Canada regulation which allows the bulk importation of drugs into the country for urgent public health needs.

Given the current opioid crisis in Canada, the need to effectively treat people addicted to opioids is crucial. But what role could injectable, extended-release naltrexone play? Does it help to prevent relapse? And how does it compare with naltrexone taken by mouth and other available treatments?

When the need arises for answers to important questions such as these, the healthcare community turns to CADTH — an independent agency that finds, assesses, and summarizes the research on drugs and medical devices. CADTH searched for medical studies that would help to answer questions about the role of extended-release naltrexone to treat opioid addiction. In total, 23 reports met the strict criteria to be included in the review of the evidence.

The CADTH review found that for patients with opioid addiction, extended-release naltrexone increases the length of time they are abstinent from opioids and helps keep them in treatment, compared with no active treatment, usual treatment, or treatment with buprenorphine. By contrast, oral naltrexone doesn’t appear to have the same results, although it could be useful in transitioning patients to treatment with extended-release naltrexone. No differences in patient safety were seen between the various treatment options. And although it is more expensive, extended-release naltrexone may still offer good value for the cost compared with treating patients with methadone or buprenorphine, according to studies from other countries.

Clinical practice guidelines included in the review generally recommend naltrexone if other treatments can’t be taken or if patients have already stopped taking opioids for long enough to be unlikely to experience withdrawal symptoms. In guidelines since 2015 oral naltrexone is not recommended, but the extended-release formulation is recommended if drugs like methadone or buprenorphine cannot be used, or if there are concerns that patients might not be able to stick to a more demanding treatment schedule.

Knowing the evidence on extended-release naltrexone is important for determining its role in helping to address the opioid crisis in Canada. While significant efforts are underway to decrease the amount of opioid prescriptions in Canada and explore non-opioid treatment options for pain, effective treatment of all patients already addicted to opioids is essential. It is important to identify alternative, effective drugs that can help address the challenges presented by buprenorphine or methadone treatment for opioid addiction — and based on the CADTH review of the evidence, extended-release naltrexone may offer just that.

If you’d like to learn more about the CADTH review of extended-release naltrexone or find more evidence to help address the opioid crisis in Canada, please visit: www.cadth.ca/opioids and www.cadth.ca/pain, follow us on Twitter @CADTH_ACMTS, or speak to the CADTH Liaison Officer in your region.

Dr. Janice Mann MD, is Co-lead of the CADTH Opioid Working Group.