According to the Prescribing Information for Vivitrol, it was administered during clinical trials without a test dose of oral Naltrexone for establishing tolerability. Oral Naltrexone is not necessary prior to the administration of injectable Vivitrol. However, if oral Naltrexone is being utilized, switching hasn’t been addressed in clinical trials. Theoretically, plasma concentrations of oral Naltrexone would be negligible the following day, as the half-life is short (4 hours) with 95% of the dose eliminated by 20 hours. Therefore, initiating injectable Vivitrol the day after a dose of oral Naltrexone would unlikely to lead to an unplanned serum accumulation.
As far as prescribing or administration of injectable Vivitrol, it is only available in a 380 mg IM dose, which should be given once monthly. This is equivalent to a 50 mg daily oral dose of Naltrexone.
A precaution to consider is that patients should be warned to abstain from opioids for 7-10 days prior to administration. If this is not done, there could be a precipitated withdrawal with severe withdrawal symptoms. In the case where a patient is switching from methadone onto Vivitrol, they should be instructed that they need to be completely withdrawn from the opioids/maintenance treatment. Additionally, caution for use of Vivitrol is advised in renal impairment (specifically with CrCl <50), and no hepatic dosing adjustments or cautions are established.
For alcohol use disorders, evidence shows that treatment with Vivitrol at three months or longer is most efficacious. Any prescribing provider is also eligible to administer the injection for patients.
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