Recommended Dosage of Intramuscular (IM) Naltrexone for Opioid or Alcohol Dependence
The recommended dose of intramuscular naltrexone is 380 mg administered once every 4 weeks (28 days) for both alcohol and opioid dependence. 1, 2
Dosage Details and Administration
For Injectable Extended-Release Formulation
- Standard dose: 380 mg IM injection once every 28 days 1, 2
- Administration site: Gluteal muscle via intramuscular injection 3
- Preparation: The medication comes as biodegradable polylactide-co-glycolide polymer microspheres containing 34% w/w naltrexone that are reconstituted in an aqueous suspension just prior to administration 2
For Oral Naltrexone (For Comparison)
- Initial dose: 25 mg for the first 1-3 days to assess tolerability 1
- Standard maintenance dose: 50 mg once daily 1
- Alternative dosing schedules: Can be administered daily, twice weekly, or three times weekly based on clinical needs 4
Clinical Efficacy
- IM naltrexone 380 mg has demonstrated a 25% decrease in heavy drinking days compared to placebo in alcohol-dependent patients 5
- The extended-release formulation provides continuous naltrexone exposure for 1 month, addressing the poor adherence issues associated with daily oral dosing 3
- Pharmacokinetic studies show measurable naltrexone plasma concentrations for at least 31 days after a single 380 mg IM injection 3
Patient Selection Considerations
Patients most likely to benefit from naltrexone therapy are:
- Employed and socially stable individuals 4
- Those highly motivated to maintain abstinence 4
- Patients who have been detoxified from opioid dependency for 7 or more days prior to starting treatment 4
Safety Considerations
Contraindications
- Current use of opioid analgesics
- Acute opioid withdrawal
- Failed naloxone challenge test
- Acute hepatitis or liver failure
Monitoring
- Liver function tests at baseline and every 3-6 months 1
- Assessment of treatment response at 12 weeks 1
Common Side Effects
- Injection site reactions
- Nausea and vomiting
- Headache
- Dizziness
- Arthralgia 1
Important Clinical Pearls
Naltrexone should always be used as an adjunct to a comprehensive treatment program that includes psychosocial interventions 6
The extended-release formulation avoids first-pass metabolism and changes the exposure ratio of 6β-naltrexol to naltrexone compared with oral administration 3
Treatment discontinuation rates due to adverse events are approximately 14.1% with the 380 mg dose 5
Naltrexone is not a cure for dependency but assists clinicians in addressing medical, psychological, and economic problems associated with substance use disorders 4
For patients with alcohol dependence, those who abstain completely from drinking during the 7 days prior to the first dose may experience greater reductions in drinking days and heavy drinking days 2