Flumazenil (also known as flumazepil, code name Ro 15-1788) is a selective GABA_A receptor antagonist administered via injection, otic insertion, or intranasally. Therapeutically, it acts as both an antagonist and antidote to benzodiazepines (particularly in cases of overdose), through

competitive inhibition Competitive inhibition is interruption of a chemical pathway owing to one chemical substance inhibiting the effect of another by competing with it for binding or bonding. Any metabolic or chemical messenger system can potentially be affected b ...

. It was first characterized in 1981, and was first marketed in 1987 by

Hoffmann-La Roche F. Hoffmann-La Roche AG, commonly known as Roche, is a Swiss multinational healthcare company that operates worldwide under two divisions: Pharmaceuticals and Diagnostics. Its holding company, Roche Holding AG, has shares listed on the SIX ...

under the trade name Anexate. However, it did not receive FDA approval until December 20, 1991. The developer lost its exclusive patent rights in 2008; so at present, generic formulations of this drug are available. Intravenous flumazenil is primarily used to treat benzodiazepine overdoses and to help reverse anesthesia. Administration of flumazenil by

sublingual Sublingual ( abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their pr ...

lozenge and topical cream has also been tested.

Medical uses

Flumazenil benefits patients who become excessively drowsy after use of

benzodiazepine Benzodiazepines (BZD, BDZ, BZs), sometimes called "benzos", are a class of depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed to treat conditions such as anxiety disorders, ...

s for either

diagnostic Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems engine ...

therapeutic A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis. As a rule, each therapy has indications and contraindications. There are many differe ...

procedures. The drug has been used as an

antidote An antidote is a substance that can counteract a form of poisoning. The term ultimately derives from the Greek term φάρμακον ἀντίδοτον ''(pharmakon) antidoton'', "(medicine) given as a remedy". Antidotes for anticoagulants are s ...

in the treatment of benzodiazepine overdoses. It reverses the effects of benzodiazepines by

at the benzodiazepine (BZ) recognition site on the GABA/benzodiazepine receptor complex. There are many complications that must be taken into consideration when used in the

acute care Acute care is a branch of secondary health care where a patient receives active but short-term treatment for a severe injury or episode of illness, an urgent medical condition, or during recovery from surgery.Alberta Health ServicesAcute care.Acc ...

setting. These include lowered seizure threshold, agitation, and anxiousness. Flumazenil's short half-life requires multiple doses. Because of the potential risks of withdrawal symptoms and the drug's short half-life, patients must be carefully monitored to prevent recurrence of overdose symptoms or adverse side effects. Flumazenil is also sometimes used after surgery to reverse the sedative effects of benzodiazepines. This is similar to

naloxone Naloxone, sold under the brand names Narcan (4 mg) and Kloxxado (8 mg) among others, is a medication used to reverse or reduce the effects of opioids. It is commonly used to counter decreased breathing in opioid overdose. Effects begin withi ...

's application to reverse the effect of

opiates An opiate, in classical pharmacology, is a substance derived from opium. In more modern usage, the term ''opioid'' is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain (including antagonist ...

and

opioids Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...

following surgery. Administration of the drug requires careful monitoring by an anesthesiologist due to potential side effects and serious risks associated with over-administeration. Likewise, post-surgical monitoring is also necessary because flumazenil can mask the apparent metabolization ("wearing off") of the drug after removal of patient life-support and monitoring equipment. Flumazenil has been effectively used to treat overdoses of non-benzodiazepine hypnotics, such as zolpidem, zaleplon and zopiclone (also known as "Z-drugs"). It may also be effective in reducing

excessive daytime sleepiness Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompass ...

while improving

vigilance Vigilance may refer to: * Alertness * Vigilance, a creature ability in the ''Magic: The Gathering'' collectible card game * ''Vigilance'' (album), by Threat Signal * Vigilance (behavioural ecology), the watchfulness of prey for nearby predator ...

in primary hypersomnias, such as idiopathic hypersomnia. The drug has also been used in

hepatic encephalopathy Hepatic encephalopathy (HE) is an altered level of consciousness as a result of liver failure. Its onset may be gradual or sudden. Other symptoms may include movement problems, changes in mood, or changes in personality. In the advanced stage ...

. It may have beneficial short‐term effects in people with

cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...

, but there is no evidence for long-term benefits. The onset of action is rapid, and effects are usually 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, up to a maximum of 3 mg per hour. It is available as a clear, colourless solution for

intravenous injection Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...

, containing 500 μg in 5 mL. Additional doses may be needed within 20 to 30 min if evidence of oversedation reappears. Many benzodiazepines (including

midazolam Midazolam, sold under the brand name Versed among others, is a benzodiazepine medication used for anesthesia and procedural sedation, and to treat severe agitation. It works by inducing sleepiness, decreasing anxiety, and causing a loss of ...

) have longer half-lives than flumazenil. Therefore, in cases of overdose, repeat doses of flumazenil may be required to prevent recurrent

symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...

s once the initial dose of flumazenil wears off. It is hepatically metabolised to inactive compounds which are excreted in the urine. Individuals who are physically dependent on benzodiazepines may experience

benzodiazepine withdrawal Benzodiazepine withdrawal syndrome often abbreviated to benzo withdrawal or BZD withdrawal is the cluster of signs and symptoms that may emerge when a person who has been taking benzodiazepines, either medically or recreationally develops a phy ...

symptoms, including

seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with l ...

, upon rapid administration of flumazenil. It is not recommended for routine use in those with a decreased level of consciousness. In terms of drug enforcement initiatives, diversion control programs and required post-marketing surveillance of adverse events, orders for flumazenil may trigger a prescription audit to the search for benzodiazepine misuse and for clinically significant adverse reactions related to their use.

PET radioligand

Radiolabeled with the radioactive isotope

carbon-11 Carbon (6C) has 15 known isotopes, from to , of which and are stable. The longest-lived radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenically by ...

, flumazenil may be used as a

radioligand A radioligand is a radioactive biochemical substance (in particular, a ligand that is radiolabeled) that is used for diagnosis or for research-oriented study of the receptor systems of the body. In a neuroimaging application the radioligand is ...

neuroimaging Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incr ...

with

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

to visualize the distribution of GABA_A receptors in the human brain.

Treatment for benzodiazepine dependence & tolerance

Epileptic patients who have become tolerant to the anti-seizure effects of the benzodiazepine clonazepam became seizure-free for several days after treatment with 1.5 mg of flumazenil. Similarly, patients who were dependent on high doses of benzodiazepines (median dosage 333 mg diazepam-equivalent) were able to be stabilised on a low dose of clonazepam after 7–8 days of treatment with flumazenil. Flumazenil has been tested against placebo in benzo-dependent subjects. Results showed that typical benzodiazepine withdrawal effects were reversed with few to no symptoms. Flumazenil was also shown to produce significantly fewer withdrawal symptoms than saline in a randomized, placebo-controlled study with benzodiazepine-dependent subjects. Additionally, relapse rates were much lower during subsequent follow-up.

In vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and ...

studies of tissue cultured cell lines have shown that chronic treatment with flumazenil enhanced the benzodiazepine binding site where such receptors have become more numerous and uncoupling/down-regulation of GABA_A has been reversed. After long-term exposure to benzodiazepines, GABA_A receptors become down-regulated and uncoupled. Growth of new receptors and recoupling after prolonged flumazenil exposure has also been observed. It is thought this may be due to increased synthesis of receptor proteins. Flumazenil was found to be more effective than placebo in reducing feelings of hostility and aggression in patients who had been free of benzodiazepines for 4–266 weeks. This may suggest a role for flumazenil in treating protracted benzodiazepine withdrawal symptoms. Low-dose, slow

subcutaneous Subcutaneous may refer to: * Subcutaneous injection * Subcutaneous tissue The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The ...

flumazenil administration is a safe procedure for patients withdrawing from long-term, high-dose benzodiazepine dependency. It has a low risk of seizures even amongst those who have experienced convulsions when previously attempting benzodiazepine withdrawal. In Italy, the gold standard for treatment of high-dose benzodiazepine dependency is 8–10 days of low-dose, slowly infused flumazenil. One addiction treatment centre in Italy has used flumazenil to treat over 300 patients who were dependent on high doses of benzodiazepines (up to 70 times higher than conventionally prescribed) with physicians being among the clinic's most common patients.

Clinical pharmacology

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. It also exhibits weak partial agonism of GABA_A receptor complexes that contain α₆-type monomers; the clinical relevance of this is unknown. Flumazenil does not antagonize all of the central nervous system effects of drugs affecting GABA-ergic neurons by means other than the benzodiazepine receptor (including ethanol, barbiturates, and most anesthetics) and does not reverse the effects of opioids. It will however antagonize the action of non-benzodiazepine z-drugs, such as zolpidem and zopiclone, because they act via the benzodiazepine site of the GABA receptor - it has been used to successfully treat z-drug overdose.

Pharmacodynamics

Intravenous flumazenil has been shown to antagonize

sedation Sedation is the reduction of irritability or agitation by administration of sedative drugs, generally to facilitate a medical procedure or diagnostic procedure. Examples of drugs which can be used for sedation include isoflurane, diethyl ethe ...

, 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.

Availability

Flumazenil is sold under a wide variety of brand names worldwide like Anexate, Lanexat, Mazicon, Romazicon. In India it is manufactured by Roche Bangladesh Pharmaceuticals and USAN Pharmaceuticals.

References

Other

Romazicon product information
Roche USA

External links

* * {{GABA receptor modulators Antidotes Anxiogenics Carboxylate esters Chemical substances for emergency medicine Convulsants GABAA receptor negative allosteric modulators Hoffmann-La Roche brands Imidazobenzodiazepines Lactams Fluoroarenes