Flumazenil

A vial of flumazenil solution for injection

Flumazenil (also known as flumazepil, code name Ro 15-1788, trade names Anexate, Lanexat, Mazicon, Romazicon) is a benzodiazepine antagonist.

It was introduced in 1987 by Hoffmann-La Roche under the trade name Anexate.

Flumazenil is of benefit in patients who become excessively drowsy after benzodiazepines are used for either diagnostic or therapeutic procedures.

It has been used as an antidote in the treatment of benzodiazepine overdoses. It reverses the effects of benzodiazepines by competitive inhibition at the benzodiazepine binding site on the GABA_A receptor. There are many complications that must be taken into consideration when used in the acute care setting.

It has been found to be effective in overdoses of non-benzodiazepine sleep enhancers, namely zolpidem and zaleplon.

It has also been used in hepatic encephalopathy, though results have been mixed.

The onset of action is rapid and usually effects are seen within one to two minutes. The peak effect is seen at six to ten minutes. The recommended dose for adults is 200 μg every 1–2 minutes until the effect is seen, to a maximum of 3 mg per hour. It is available as a clear, colourless solution for intravenous injection, containing 500 μg in 5 mL.

Many benzodiazepines (including midazolam) have longer half-lives than flumazenil. Therefore, repeat doses of flumazenil may be required to prevent recurrent symptoms of overdosage once the initial dose of flumazenil wears off. It is hepatically metabolised to inactive compounds which are excreted in the urine. Subjects who are physically dependent on benzodiazepines may suffer benzodiazepine withdrawal symptoms, including seizure, upon administration of flumazenil.

It is not recommended for routine use in those with a decreased level of consciousness.

PET radioligand

Radiolabeled with the radioactive isotope carbon-11 flumazenil may be used as a radioligand in neuroimaging with positron emission tomography to visualize the distribution of GABA_A receptors in the human brain.

Flumazenil, an imidazobenzodiazepine derivative, antagonizes the actions of benzodiazepines on the central nervous system. Flumazenil competitively inhibits the activity at the benzodiazepine recognition site on the GABA / benzodiazepine receptor complex. Flumazenil is a weak partial agonist in some animal models of activity, but has little or no agonist activity in humans.

Flumazenil does not antagonize the central nervous system effects of drugs affecting GABA-ergic neurons by means other than the benzodiazepine receptor (including ethanol, barbiturates, or general anesthetics) and does not reverse the effects of opioids.

In animals pretreated with high doses of benzodiazepines over several weeks, Flumazenil injection elicited symptoms of benzodiazepine withdrawal, including seizures. A similar effect was seen in adult human subjects.

Intravenous Flumazenil has been shown to antagonize sedation, impairment of recall, psychomotor impairment and ventilatory depression produced by benzodiazepines in healthy human volunteers.

The duration and degree of reversal of sedative benzodiazepine effects are related to the dose and plasma concentrations of Flumazenil.

• Romazicon product information, Roche USA