Naloxone, Naltrexone, and MethylNaltrexone
Naltrexone is a longer acting agent than naloxone and is used more for long-term needs. Naloxone, on the other hand, acts fast and is used to reverse opioid effects quickly, as in opioid overdose.
| Agent | Mechanism of Action* | Use | Common Adult Doses | Comments |
| Naloxone (Narcan) |
Antagonizes various opioid receptors (Opioid antagonist) | – Opioid overdose – Opioid reversal, full – Opioid reversal, partial |
For Opioid Overdose: Naloxone 0.4-2mg SC/IM/IV q2-3 min prn Info: May repeat q1-2h if sx recur; reassess tx if no response after 10mg. |
Duration: 0.5 to 2h depending on the route. IV has a shorter duration of action than IM route. **Since naloxone’s action is shorter than that of most opioids, repeated doses are usually needed. |
| Naltrexone | Antagonizes various opioid receptors (Opioid antagonist) | – Opioid addiction – Alcohol dependence |
Opiod addiction: 50mg PO QD Start 25mg po x 1, repeat in 1h if no withdrawal. Info: Must be opioid-free 7-10 days; consider naloxone challenge test if risk of withdrawal suspected. |
Duration: Oral: 50mg: 24hrs; 100mg: 48hrs; 150mg 72hrs; IM: 4 weeks |
| MethylNaltrexone (Relistor) |
Selectively antagonizes peripheral mu-opioid receptors, inhibiting opioid-induced GI hypomotility (peripheral mu-opioid antagonist) | Opioid-induced constipation | 12mg SC qd for chronic non-cancer pain patients
For palliative patients, it is given qod prn and is weight based. Check Epocrates or another resource. |
Naloxegol (Movantik) – Peripheral Opioid Antagonists
selectively antagonizes peripheral mu-opioid receptors, inhibiting opioid-induced GI hypomotility (peripheral mu-opioid antagonist)
*From Epocrates