Nalmefene hydrochloride may be administered by IV, IM, or subcutaneous injection.1
The manufacturer states that safety and efficacy of nalmefene hydrochloride in children younger than 18 years of age have not been established.1 However, the drug can be used in the reversal of opiate effects in neonates when, in the opinion of the clinician, the potential benefits are expected to outweigh the risks.1
Dosage of nalmefene hydrochloride is expressed in terms of the base.1
When used to partially reverse opiate depression following the use of opiates during surgery, the usual initial dosage of nalmefene is 0.25 mcg/kg given at 2- to 5-minute intervals until the desired response is obtained.1 A cumulative total dosage exceeding 1 mcg/kg does not provide additional therapeutic effect.1 Patients who are at increased cardiovascular risk should receive an initial dosage of 0.1 mcg/kg given at 2- to 5- minute intervals until desired response is obtained.1 The goal of postoperative nalmefene therapy is to reverse excessive opiate effects without completely reversing opiate analgesia, which could precipitate acute pain.1 When used postoperatively, the manufacturer recommends that the commercially available injection containing 100 mcg/mL of the drug be used; in patients with increased cardiovascular risk, it may be desirable to further dilute the injection to a final ratio of 1:1 in 0.9% sodium chloride injection or sterile water for injection.1
For the treatment of known opiate overdosage or as an aid in the diagnosis of suspected opiate overdosage, the usual initial adult dosage of nalmefene is 7.14 mcg/kg (0.5 mg/70 kg), followed by a second dose of 14.29 mcg/kg (1 mg/70 kg) 2-5 minutes later, if necessary.1 For these uses, the manufacturer recommends that the commercially available injection containing 1 mg/mL of the drug be used.1 If no response is observed after a total dose of 21.43 mcg/kg (1.5 mg/70 kg) of the drug has been administered, additional doses of the drug are unlikely to provide therapeutic effect.1
Patients suspected of opiate dependency should receive an initial dosage of 1.43 mcg/kg (100 mcg/70 kg); if no withdrawal is observed within 2 minutes, the recommended dosage for opiate overdosage can be given.1
Nalmefene hydrochloride is the longest acting of the currently available parenteral opiate antagonists.1 However, if recurrence of respiratory depression occurs, dosage of nalmefene should be titrated incrementally again to response in order to avoid over-reversal of opiate effects.1
Dosage in Hepatic and Renal Impairment 
Although hepatic and renal impairment may substantially reduce clearance of nalmefene, adjustment of dosage of the drug is not needed for single episodes of opiate antagonism.1 However, in patients with renal failure, the incremental doses should be administered slowly (e.g., over 60 seconds) to minimize hypertension and dizziness associated with rapid administration of the drug in such patients.1