Nefopam, sold under the brand name Acupan among others, is a centrally acting, non-opioid analgesic, with central stimulant and sympathomimetic properties that is primarily used to treat moderate to severe pain.
History
Nefopam is based on a benzoxazocine compound. It was developed in the 1960s and marketed under the name fenazocine.
It was initially used in shivering, as a muscle relaxant and as an antidepressant, but then increasingly as an analgesic.
Medical uses
Analgesic
Nefopam was significantly more effective than
aspirin as an analgesic in one clinical trial,
although with a greater incidence of side effects such as sweating, dizziness and nausea, especially at higher doses.
The estimated relative potency of nefopam to morphine indicates that 20 mg of nefopam HCl is the approximate analgesic equal of 12 mg of morphine with comparable analgesic efficacy to morphine,
Postoperative pain
A 2025 review, covering 17 studies, found that nefopam was an effective adjunctive postoperative analgesic with benefits in pain management, and correlated with a mean decrease in opioid consumption across the studies of 38%. Adverse effects were not discussed in detail in the included studies.
Chronic pain
For
chronic pain nefopam may sometimes be used when common alternatives are contraindicated or ineffective, or as an add-on therapy.
Other Medical Uses
Nefopam is used to treat severe
hiccups.
Nefopam is thought to have some efficacy for treating (off-label) Parkinson's disease, in a similar fashion to those of Bupropion and Methylphenidate.
Nefopam is effective for prevention of shivering during surgery or recovery from surgery.
Contraindications
Nefopam is contraindicated in people with convulsive disorders, those that have received treatment with irreversible monoamine oxidase inhibitors such as
phenelzine,
tranylcypromine or
isocarboxazid within the past 30 days and those with myocardial infarction pain, mostly due to a lack of safety data in these conditions.
Side effects
Common side effects include nausea, nervousness, dry mouth, light-headedness and urinary retention.
Less common side effects include vomiting, blurred vision, drowsiness, sweating, insomnia, headache, confusion, hallucinations, tachycardia, aggravation of angina and rarely a temporary and benign pink discolouration of the skin or erythema multiforme.
CNS side effects
Some side effects, such as feeling confused or hallucinating, are more likely in patients over 65 years old.
Nefopam has been shown to have anticholinergic properties
Overdose
Overdose and death have been reported with nefopam.
Overdose usually manifests with
,
,
tachycardia, and hyperdynamic circulation.
Treatment is usually supportive, managing cardiovascular complications with
beta blockers and limiting absorption with activated charcoal.
Interactions
Nefopam has additive
anticholinergic and sympathomimetic effects with other agents with these properties.
Its use should be avoided in people receiving some types of antidepressants (tricyclic antidepressants or monoamine oxidase inhibitors) as there is the potential for serotonin syndrome or hypertensive crises to result.
Mechanisms of action
The mechanism of action of nefopam and its
analgesic effects are not well understood.
Analgesic mechanisms of action
Nefopam may have three analgesic mechanisms in the brain and spinal cord;
-
inhibition of long-term potentiation mediated by NMDA receptor from the inhibition of calcium influx.
Pharmacology
A 2025 review noted a significant literature gap on the
pharmacokinetic and
pharmacodynamic properties of nefopam.
+ Nefopam | Ki (nM) |
| 29 |
| 33 |
| 531 |
| 1,685 |
| 330 |
| 56 |
|
Pharmacokinetics
The absolute bioavailability of nefopam is low.
It is reported to achieve therapeutic plasma concentrations between 49 and 183 nM.
The drug is approximately 73% protein-bound across a plasma range of 7 to 226 ng/mL (28–892 nM).
The
metabolism of nefopam is
hepatic, by
N-
demethylation and via other
metabolic route.
Its terminal half-life is 3 to 8 hours, while that of its active metabolite, desmethylnefopam, is 10 to 15 hours.
It is eliminated mostly in
urine, and to a lesser extent in
feces.
Chemistry
Nefopam is a
cyclic compound analogue of
orphenadrine,
diphenhydramine, and
tofenacin, with each of these compounds different from one another only by the presence of one or two
.
The ring system of nefopam is a benzoxazocine system.
Use by country
Nefopam is used in the UK, under prescription only,
although some UK regions do not advise initiation of use.
It is used in France,
although some concerns have been raised.
As of 2014 Nefopam was not FDA-approved in the US.
Society and culture
Recreational use
Recreational use of nefopam has rarely been reported,
and is far less common than with opioid analgesics.
See also
