What is the recommended protocol for switching a patient from Vivitrol (naltrexone) 389mcg to oral Naltrexone?

Switching from Vivitrol to Oral Naltrexone

Simply discontinue Vivitrol and initiate oral naltrexone 50 mg daily when the next monthly injection would have been due—no tapering, bridging, or washout period is required since both formulations contain the same active opioid antagonist. 1

Understanding the Formulations

• Vivitrol is an extended-release injectable naltrexone formulation delivering 380 mg intramuscularly once monthly, maintaining therapeutic plasma levels for approximately 28-30 days 1, 2
• Oral naltrexone is available as 50 mg tablets taken daily, or alternatively 100 mg on Mondays and Wednesdays with 150 mg on Fridays for supervised dosing 1
• Both formulations work identically as competitive mu-opioid receptor antagonists—the only difference is the delivery system and duration of action 3, 4

Switching Protocol

When the patient is due for their next Vivitrol injection (28-30 days after the last injection), simply start oral naltrexone 50 mg daily instead of administering the injection. 1, 3

• No overlap period is needed because Vivitrol's therapeutic effect wanes by day 28-30, creating a natural transition point 2, 5
• No dose adjustment is required—the standard 50 mg daily oral dose provides equivalent opioid receptor blockade to the monthly 380 mg injection 1, 2
• No tapering is necessary since you are continuing the same medication via a different route, not discontinuing naltrexone therapy 1

Critical Safety Considerations

Ensure the patient remains completely opioid-free throughout the transition, as naltrexone in any form will precipitate severe withdrawal if opioids are present. 1, 6

• Verify the patient has been opioid-free for at least 7-10 days before the original Vivitrol initiation and maintains abstinence during the switch 7, 1
• Warn patients that discontinuing naltrexone entirely (not switching formulations) dramatically increases overdose risk due to decreased opioid tolerance 1
• Monitor liver function tests every 3-6 months regardless of formulation, as hepatotoxicity risk exists with both oral and injectable naltrexone 1, 7

Adherence and Monitoring Considerations

The primary reason for switching from injectable to oral naltrexone is typically cost, access, or patient preference—but recognize that adherence will likely decrease with daily oral dosing. 2, 5

• Injectable naltrexone was specifically developed to overcome poor adherence with daily oral dosing, which represents the main limitation of oral naltrexone therapy 2, 4
• Between 23-62% of patients remain in oral naltrexone treatment after only 3-4 weeks in non-comparative trials, with high attrition rates being the norm 4, 6
• Consider supervised dosing schedules (100 mg Monday/Wednesday, 150 mg Friday) if adherence becomes problematic 1

Supporting the Transition

Combine the formulation switch with intensified psychosocial support, as naltrexone alone—regardless of formulation—is insufficient without comprehensive behavioral therapy. 1, 6, 4

• Naltrexone works best in highly motivated patients with strong family support, stable employment, and active participation in counseling 6, 4
• Schedule more frequent follow-up visits (at least monthly) during the first 3 months after switching to oral naltrexone to monitor adherence 1
• Provide opioid overdose education and naloxone to all patients, as the risk increases if naltrexone is discontinued entirely 1

Common Pitfalls to Avoid

• Do not attempt to "bridge" with overlapping doses—this provides no benefit and wastes medication since both formulations contain identical active drug 1, 2
• Do not reduce the oral dose below 50 mg daily thinking it needs to be "tapered up"—the standard dose is required for adequate opioid receptor blockade 1, 4
• Do not switch patients who require opioids for pain management, as oral naltrexone will block analgesia just as effectively as Vivitrol 1, 7
• Do not fail to address the underlying reason for switching—if it is cost-related, explore patient assistance programs for Vivitrol rather than accepting inferior adherence with oral dosing 2, 5

Special Circumstances

If the patient needs elective surgery requiring opioid analgesia, hold oral naltrexone for 2-3 days preoperatively, whereas Vivitrol would require 24-30 days. 3, 1

• This represents one clinical advantage of oral over injectable naltrexone—greater flexibility for planned procedures 3
• For emergency surgery in patients on either formulation, higher opioid doses and regional anesthesia techniques may be required 3