Naltrexone
Vivitrol · ReVia
Long-acting pure opioid receptor antagonist
Competitive antagonist at μ, κ, δ opioid receptors. Long half-life makes it useful for opioid use disorder maintenance — but poses major perioperative challenges if patients with chronic naltrexone need opioid analgesia.
Indications
- •Opioid use disorder relapse prevention
- •Alcohol use disorder (reduces craving and reward)
- •NOT for acute reversal — onset too slow
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Oral OUD/AUD | 50 mg PO daily | — |
| IM depot | 380 mg IM gluteal q4 weeks (Vivitrol) | — |
Pharmacokinetics
Oral onset 1 h, peak 1 h, half-life 4 h (active metabolite 13 h). IM depot: blocks opioid effect for 4 weeks. Hepatic metabolism (extensive first-pass).
Hemodynamic effects
Minimal direct effect.
Respiratory effects
None directly.
Side effects
- !Precipitates severe acute withdrawal in opioid-dependent patients (must be opioid-free 7–10 d before starting)
- !Hepatotoxicity at high doses (liver function panel q3 mo)
- !Injection-site reactions for IM depot
Contraindications
- ×Active opioid use
- ×Acute opioid withdrawal
- ×Severe hepatic failure
- ×Patients requiring chronic opioid analgesia
Clinical pearls
- ★PERIOPERATIVE PLANNING: oral naltrexone — stop 72 h preop. IM depot — coordinate with prescriber; opioid blockade lasts the full 4 weeks. Use multimodal (regional, ketamine, dexmedetomidine, NSAIDs, IV acetaminophen) for analgesia.
- ★RELAPSE RISK: post-op opioid bolus once depot wears off can cause respiratory arrest from re-sensitized μ receptors. Patient education is critical.
- ★ALCOHOL EFFECT: reduces alcohol-related dopamine reward; not a sobriety guarantee, just a craving reduction.
- ★PARTIAL AGONISTS: buprenorphine + naltrexone — mutually antagonistic. Don't combine.
Other drugs in Narcotic Reversals
- Naloxone
Competitive antagonist at mu (μ), kappa, and delta opioid receptors with highest affinity for μ. Reverses respiratory depression, sedation, analgesia, miosis, pruritus, GI hypomotility from exogenous opioids.
- Methylnaltrexone
Quaternary derivative of naltrexone — does NOT cross the blood-brain barrier. Reverses peripheral opioid effects (constipation, urinary retention, pruritus) without antagonizing central analgesia.
Browse all classes: /reference/drugs
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
