Nalmefene

opioid antag.

What it isLong-acting opioid receptor antagonist used intranasally for emergency reversal of known or suspected opioid overdose.

Why this oneIts duration is longer than naloxone’s and may better match long-acting or high-potency synthetic opioids.

What limits itIt can precipitate severe, prolonged withdrawal and does not replace ventilation, repeat dosing, surveillance, or emergency care.

FDA-approved for

FDA dosing	Population	Start	Target	Max
Opioid overdose (emergency reversal)	Adults & peds ≥12 yr	1.5 mg IM/SC	1.5 mg IM/SC	repeat q2–5 min PRN (new auto-injector each dose)

Renal No adjustment needed for single episodes of opioid antagonism (clearance reduced in impairment)

Hepatic No adjustment needed for single episodes of opioid antagonism (clearance reduced in impairment)

Repeat every 2–5 min with a new auto-injector until emergency help arrives

IM/SC into anterolateral (outer) thigh only, through clothing if needed
Single-use auto-injector; do not prime or reuse
Seek emergency medical care immediately after first dose
Re-administer with a new auto-injector every 2–5 min if no response or relapse into respiratory depression

Recurrent respiratory/CNS depression — keep under surveillance
Limited efficacy vs partial/mixed opioid agonists (e.g., buprenorphine); repeat doses may be needed
May precipitate severe opioid withdrawal (life-threatening in neonates)
Abrupt reversal may cause adverse cardiovascular effects (esp. preexisting CV disease)
Attempts to overcome the blockade with opioids can cause intoxication and death

Pregnancy No human data; do not withhold for opioid overdose; no embryo-fetal harm in animals

Lactation No human data; present in rat milk

NO BOXED WARNINGS

Principal risksevere, prolonged precipitated opioid withdrawal

Cost, est. cash$75–$200/2-dose kit

Generic entryBy 2023

Therapeutic safety burden1 / 4

Overdose danger0 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk2 / 4

Legacy pregnancy categoryC

Defining liabilityUsually well tolerated; abrupt opioid withdrawal can be severe and prolonged.

no kinetic interactions