Vivitrol is an extended-release injectable formulation of naltrexone, administered as an intramuscular injection once a month. Naltrexone is an opioid-receptor antagonist that blocks the euphoric effects of opioids. Unlike other treatments for opioid use disorder, including buprenorphine/naloxone and methadone, naltrexone is not associated with the development of tolerance and dependence, and lacks the potential for misuse and diversion. However, because the oral formulation requires a daily dosage, poor adherence to the medication has limited its efficacy for the prevention of relapse in patients with opioid use disorder. The extended-release injectable formulation of naltrexone was developed to improve treatment adherence and retention.
Vivitrol has not received marketing approval in Canada and is available only for research purposes or through Health Canada’s Special Access Programme for the treatment of opioid use disorder or alcohol use disorder. In October 2010, the US FDA approved Vivitrol for the prevention of relapse to opioid dependence following opioid detoxification. Before starting Vivitrol, an opioid-free period of a minimum of seven to 10 days is recommended to avoid precipitating withdrawal, symptoms of which may be severe enough to require hospitalization. There are currently no recommendations to guide the duration of treatment with Vivitrol.
Results from one phase III, randomized, placebo-controlled, double-blind trial in patients with opioid use disorder who had recently undergone detoxification showed Vivitrol to be superior to placebo for improving abstinence and treatment retention, as well as for reducing opioid cravings over a six-month treatment period. Approximately one-half of patients who received Vivitrol for an additional year in an open-label extension study remained abstinent from opioids.
Preliminary evidence from phase III trials and studies in real-world clinical settings demonstrates that Vivitrol may be beneficial for preventing relapse in two subpopulations: people living within the corrections system and people living with HIV.
None of the phase III trials reported deaths due to overdose in patients receiving Vivitrol. The majority of commonly reported adverse effects, including nasopharyngitis (cold symptoms), insomnia, hypertension, influenza, and injection-site pain, were mild or moderate. Abnormal liver function test results occurred primarily in patients with existing hepatitis C infection, but were transient and not clinically significant. Severe injection-site reactions were noted in some patients.
There are several clinical challenges and knowledge gaps associated with the initiation, long-term use, and role of Vivitrol relative to other treatments for opioid use disorder. These will need to be addressed when considering adopting Vivitrol in clinical practice. They include the approach to transitioning patients from other treatments (including methadone or buprenorphine/naloxone) to treatment with Vivitrol, pain management, duration of treatment, long-term risk of relapse and opioid overdose, efficacy and cost compared with other therapies for opioid use disorder, and use in certain subpopulations. When considering adopting Vivitrol in clinical practice, the requirement for total abstinence from opioids for seven to 10 days before initiating treatment may present a challenge.
A Risk Evaluation and Mitigation Strategy, consisting of directions for proper injection technique and patient counselling materials, is in place in the US to inform health care providers and patients about the potentially serious risks associated with the use of Vivitrol, including severe injection-site reactions, sudden opioid withdrawal during treatment initiation, vulnerability to opioid overdose, and hepatotoxicity (drug-induced liver damage).
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