Is it safe to switch to oral naltrexone (Naltrexone) soon after a Vivitrol (Naltrexone) shot?

Switching from Vivitrol to Oral Naltrexone

Yes, it is safe to switch to oral naltrexone soon after a Vivitrol injection, as both formulations contain the same active ingredient (naltrexone) and there is no risk of drug interaction or adverse effects from overlapping coverage. 1

Pharmacokinetic Rationale

• Extended-release naltrexone (Vivitrol) provides therapeutic naltrexone levels for approximately 28-30 days after a single 380 mg intramuscular injection 2, 3
• Oral naltrexone has a plasma half-life of only 4 hours, with its active metabolite (6-β-naltrexol) having a 13-hour half-life, meaning antagonist effects persist for 2-3 days after stopping 1, 4
• Because both formulations work through the same mechanism (competitive opioid receptor antagonism), transitioning from the long-acting to short-acting form creates no pharmacological conflict 4

Timing Considerations

• You can initiate oral naltrexone at any point after a Vivitrol injection without waiting for the extended-release formulation to clear 1
• The primary clinical scenario requiring attention is the reverse situation: when switching FROM oral naltrexone TO Vivitrol, no special precautions are needed beyond ensuring the patient remains opioid-free 5
• If a patient requires opioid analgesia, the extended-release formulation must be held 24-30 days after the last injection, whereas oral naltrexone only requires 2-3 days of discontinuation 1, 6

Clinical Context for Switching

• The most common reason for switching from Vivitrol to oral naltrexone is patient preference, cost considerations, or the need for more flexible dosing control 7
• Oral naltrexone can be dosed daily (50 mg) or on alternative schedules (100 mg Monday/Wednesday, 150 mg Friday) to improve adherence 8, 7
• Some patients may prefer oral naltrexone because it allows them to discontinue therapy more quickly if opioid analgesia becomes necessary (2-3 days vs 24-30 days) 1, 6

Critical Safety Warnings

• The primary concern with naltrexone therapy is NOT the switch between formulations, but rather ensuring the patient was completely opioid-free for 7-10 days before starting ANY naltrexone formulation 5
• Patients who discontinue naltrexone (either formulation) have markedly increased risk of opioid overdose and death due to loss of opioid tolerance during treatment 6, 8
• If precipitated withdrawal occurs from premature naltrexone administration, it can be severe enough to require hospitalization, particularly with the extended-release formulation 5, 9

Common Pitfall to Avoid

• Do not confuse this question with switching FROM buprenorphine or methadone TO naltrexone, which requires careful management and up to 2 weeks of vulnerability to precipitated withdrawal 5
• The FDA explicitly warns that patients transitioning from buprenorphine or methadone may experience severe precipitated withdrawal for as long as 2 weeks, but this does not apply to switching between naltrexone formulations 5