Nalmefene

Nalmefene

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Systematic (IUPAC) name
17-cyclopropylmethyl-4,5α-epoxy-6-methylenemorphinan-3,14-diol
Clinical data
Routes of administration	Oral, Intravenous
Legal status
Legal status	Prescription Only Medicine
Pharmacokinetic data
Protein binding	45%
Metabolism	hepatic
Biological half-life	10.8 ± 5.2 hours
Excretion	renal
Identifiers
CAS Number	55096-26-9 58895-64-0 (HCl)
ATC code	none
Chemical data
Formula	C21H25NO3
Molar mass	375.9 g/mol (hydrochloride)[[]]

Nalmefene (Revex) is an opioid receptor antagonist used primarily in the management of alcohol dependence, and also has been investigated for the treatment of other addictions such as pathological gambling and addiction to shopping.

Nalmefene is an opiate derivative similar in both structure and activity to the opiate antagonist naltrexone. Advantages of nalmefene relative to naltrexone include longer half-life, greater oral bioavailability and no observed dose-dependent liver toxicity. As with other drugs of this type, nalmefene can precipitate acute withdrawal symptoms in patients who are dependent on opioid drugs, or more rarely when used post-operatively to counteract the effects of strong opioids used in surgery.

Nalmefene differs from naltrexone by substitution of the ketone group at the 6-position of naltrexone with a methylene (CH₂) group, which considerably increases binding affinity to the μ-opioid receptor. Nalmefene also has high affinity for the other opioid receptors, and is known as a "universal antagonist" for its ability to block all three.

In clinical trials using this drug, doses used for treating alcoholism were in the range of 20-80 mg per day, orally. The doses tested for treating pathological gambling were between 25-100 mg per day. In both trials, there was little difference in efficacy between the lower and higher dosage regimes, and the lower dose (20 and 25 mg, respectively) was the best tolerated, with similar therapeutic efficacy to the higher doses and less side effects. Nalmefene is thus around twice as potent as naltrexone when used for the treatment of addictions.

Intravenous doses of nalmefene at between 0.5 to 1 milligram have been shown effective at counteracting the respiratory depression produced by opiate overdose , although this is not the usual application for this drug as naloxone is less expensive.

Doses of nalmefene greater than 1.5 mg do not appear to give any greater benefit in this application. Nalmefene's longer half-life might however make it useful for treating overdose involving longer acting opioids such as methadone, as it would require less frequent dosing and hence reduce the likelihood of renarcotization as the antagonist wears off.

Nalmefene is extensively metabolised in the liver, mainly by conjugation with glucuronic acid and also by N-dealkylation. Less than 5% of the dose is excreted unchanged. The glucuronide metabolite is entirely inactive, while the N-dealkylated metabolite has minimal pharmacological activity.

Side effects

• Common: drowsiness, hypertension, tachycardia, dizziness, nausea, vomiting
• Occasional: fever, hypotension, vasodilatation, chills, headache
• Rare: agitation, arrhythmia, bradycardia, confusion, hallucinations, myoclonus, itching

Properties

• Soluble in water up to 130mg/mL, soluble in chloroform up to 0.13 mg/mL
• pK_a 7.6
• Distribution half-life: 41 minutes

References

pl:Nalmefen