Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Available forms1 form · 1 strength documentedShow all ↓
0.1 mg/mL 100 µg/mL5 mL vial10 mL vial human-labelled — no veterinary presentation
Overview
Flumazenil (Romazicon®) is a benzodiazepine antagonist used in veterinary medicine to reverse the sedative and central nervous system effects of benzodiazepines in dogs and cats. It is given when adverse benzodiazepine effects arise or when rapid recovery from sedation or anaesthesia is required, but routine use as a reversal agent is not advised.
Flumazenil has a rapid onset of action, typically within 1–2 minutes after intravenous administration, but its duration of effect is relatively short. As a result, re-sedation may occur, especially with long-acting benzodiazepines, and repeated dosing may be necessary.
In addition to benzodiazepines, flumazenil may have activity in reversing the effects of non-benzodiazepine drugs that act on benzodiazepine receptors (e.g., zolpidem). It may also be used in specific anaesthetic protocols involving tiletamine/zolazepam in dogs, although only the zolazepam component is reversed and the tiletamine effects that remain may be made worse rather than simply persisting.
Mechanism of Action (MOA): Flumazenil acts as a competitive neutral antagonist at benzodiazepine binding sites on the GABAA receptor in the central nervous system, reversing the sedative and amnestic effects of benzodiazepines.
Indications
Flumazenil is used in dogs and cats to reverse the effects of benzodiazepines or related drugs, particularly in situations where rapid recovery or management of adverse effects is required.
- Reversal of benzodiazepine sedation: Used to counteract excessive sedation or unwanted effects following benzodiazepines given for anaesthesia or procedural sedation, and – in life-threatening cases only – a paradoxical excitatory reaction.
- Recovery from anesthetic protocols: May be used to hasten recovery when benzodiazepines are included in anesthetic combinations.
- Benzodiazepine overdose: Used in the management of toxicity associated with benzodiazepine overdose.
- Non-benzodiazepine receptor agonists: May provide benefit in overdoses of drugs acting on benzodiazepine receptors (e.g., zolpidem).
- Tiletamine/zolazepam reversal (dogs): May reverse the zolazepam component, but the tiletamine component cannot be reversed at all, and reversal of tiletamine/zolazepam anaesthesia is not commonly performed for that reason.
- Hepatic encephalopathy: For hepatic encephalopathy, flumazenil is not recommended for routine treatment because efficacy is unestablished; it may produce transient improvement and may be considered as salvage therapy in severe cases that fail standard treatment.
- Neonatal resuscitation after caesarean section: Reverses benzodiazepines given to the dam that have depressed the newborn, and repeated dosing may be needed until the neonate has cleared the anaesthetic drugs.
- Marijuana (THC) toxicosis in dogs: An uncontrolled pilot study found that a single dose might improve gait, stance and level of consciousness.
Dosage (Reference)
Dog
In dogs, flumazenil is administered intravenously for rapid reversal of benzodiazepine effects. Dosing should be titrated to effect, starting at the lowest effective dose and repeated as needed.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Benzodiazepine reversal / toxicity | IV (or IO) | 0.01 to 0.1 mg/kg | Repeat as needed | Start at 0.01 mg/kg and repeat as needed to effect; doses towards the top of the range have been used but are not supported by published data. |
| Life-threatening paradoxical reaction | IV | 0.01 mg/kg | q1-2h as needed | Flumazenil can cause seizures, so its use here is generally restricted to life-threatening reactions; do not give another benzodiazepine to control the reaction. |
| Tiletamine/zolazepam reversal | IV | 0.04–0.06 mg/kg | Repeat interval not stated | Reverses only the zolazepam component, and the tiletamine effects left behind may be made worse; dogs given 0.08 to 0.16 mg/kg for this purpose have shown seizures, salivation, shivering and opisthotonos. |
| Emergency use (no IV access) | Intratracheal | – | – | May be used in emergencies when venous access is unavailable. |
| Hepatic encephalopathy (salvage therapy) | IV | 0.02 mg/kg | Repeat interval not stated | Salvage therapy only, in severe cases that have not responded to standard treatment; any improvement is transient and has not been shown to improve recovery or survival. |
| Neonatal reversal after caesarean section | IV, IM, SC, sublingual or intranasal | 0.01 mg/kg | Repeat as needed until the neonate has cleared the anaesthetic drugs | Given to the newborn, not to the dam, when benzodiazepines used in the dam have depressed the puppies. |
| Marijuana (THC) toxicosis | IV | 0.01 mg/kg | One dose studied | Pilot evidence only; the study had no control group, and only a single injection was given. |
| Benzodiazepine reversal – fixed total dose | IV | 0.2 mg per dog | As needed | A per-animal dose, not per kilogram; an alternative to weight-based dosing for benzodiazepine reversal. |
• Titrate dose gradually to achieve reversal without overcorrection.
• If no response at higher doses, consider other causes (e.g., hypothermia or other drugs).
• Duration of action is short – about 1 hour – so re-sedation may occur and repeat dosing may be needed; peak effect is not reached until 6 to 10 minutes after the injection.
• Monitor closely for seizures, particularly in patients with pre-existing liver dysfunction or neurologic disease, and watch for the return of sedation after the drug wears off.
• In neonates after caesarean section, flumazenil 0.01 mg/kg may be given intravenously, intramuscularly, subcutaneously, sublingually or intranasally.
Cat
In cats, flumazenil is used similarly to dogs for reversal of benzodiazepine effects. Dosing is titrated carefully based on clinical response.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Benzodiazepine reversal / toxicity | IV (or IO) | 0.01 to 0.1 mg/kg | Repeat as needed | Start low and repeat as needed based on response; doses towards the top of the range have been used but are not supported by published data. |
| Life-threatening paradoxical reaction | IV | 0.01 mg/kg | q1-2h as needed | Flumazenil can cause seizures, so its use here is generally restricted to life-threatening reactions; do not give another benzodiazepine to control the reaction. |
| Hepatic encephalopathy (salvage therapy) | IV | 0.02 mg/kg | Repeat interval not stated | Salvage therapy only, in severe cases that have not responded to standard treatment; any improvement is transient and has not been shown to improve recovery or survival. |
| Neonatal reversal after caesarean section | IV, IM, SC, sublingual or intranasal | 0.01 mg/kg | Repeat as needed until the neonate has cleared the anaesthetic drugs | Given to the newborn, not to the queen, when benzodiazepines used in the queen have depressed the kittens. |
| Benzodiazepine reversal – fixed total dose | IV | 0.2 mg per cat | As needed | A fixed total dose, not a dose per kilogram; an alternative intravenous dose for benzodiazepine reversal. |
• Start at the lowest effective dose and titrate gradually.
• Re-sedation may occur due to shorter duration of flumazenil compared to benzodiazepines.
• Monitor closely for seizures, particularly in cats with liver dysfunction or a seizure disorder – flumazenil is not recommended at all in a patient with a seizure disorder.
• Ensure other sedative or anesthetic agents are considered if reversal is incomplete.
Warnings & Precautions
Flumazenil must be used cautiously due to its potential to precipitate neurologic and cardiovascular complications, particularly in high-risk patients or mixed overdose situations.
- Contraindications: Do not use in patients with known hypersensitivity, when benzodiazepines are being used to control a life-threatening condition (e.g., status epilepticus, increased intracranial pressure), or in the treatment of tricyclic antidepressant overdose.
- Mixed overdoses: Use extreme caution, especially in patients exposed to cyclic antidepressants, as reversal of benzodiazepine effects may precipitate seizures or cardiac arrhythmias.
- Head trauma: May increase the risk of seizures and alter cerebral blood flow; use cautiously.
- Non-benzodiazepine overdoses: Use with caution in suspected overdoses involving drugs such as baclofen or carisoprodol; clinical signs can worsen, and flumazenil may be contraindicated in these cases.
- Seizure risk: Increased risk in patients with liver dysfunction or neurologic disease, and human data report a greater seizure risk with severe hepatic impairment and with long-term benzodiazepine use. Flumazenil is not recommended at all in a patient with a seizure disorder, and the risk also rises when it is combined with other drugs that lower the seizure threshold.
- Reversal considerations: Routine use as a reversal agent is not advised: rare but serious reactions including cardiac arrhythmias, seizures and sudden death have been reported in humans and in experimental canine studies. For midazolam overdose specifically, supportive therapy may be more suitable in all but the largest overdoses.
- Short duration of action: Effects may wear off before the sedative drug, leading to recurrence of sedation or clinical signs.
- Pregnancy and lactation: Safety has not been established in pregnant or nursing animals, so use only when the benefit to the mother outweighs the risk to the offspring; it is not known whether flumazenil passes into milk.
Drug Interactions
Flumazenil has limited but clinically important drug interactions, primarily related to its effects on reversing benzodiazepine activity and potential to precipitate neurologic complications.
- Cyclic antidepressants (e.g., clomipramine, amitriptyline): Increased risk of seizures; use is contraindicated in patients with tricyclic antidepressant overdose.
- Neuromuscular blocking agents: Flumazenil should not be administered until neuromuscular blockade has been fully reversed.
- Imepitoin: Flumazenil could antagonise the anxiolytic and anticonvulsant effects of imepitoin.
- Drugs that lower the seizure threshold: Any drug that lowers the seizure threshold increases the risk of seizures when flumazenil is given.
Side Effects & Overdose
Side Effects
Adverse effects of flumazenil are generally dose-related and are more likely at higher doses or in predisposed patients.
- Neurologic effects (dogs): Seizures, shivering and opisthotonos, reported in dogs given higher doses of about 0.08 to 0.16 mg/kg to reverse tiletamine/zolazepam.
- Behavioral signs: Howling has been reported in dogs given higher doses; agitation is reported in people.
- Respiratory signs: Hacking cough has been reported in dogs.
- Other effects: Salivation has been reported in dogs; vomiting, cutaneous vasodilatation, vertigo, ataxia, blurred vision and cardiac arrhythmias have been reported in people.
- Injection-site reactions: May occur; give through a freely running infusion into a large vein.
Overdose
In the absence of a benzodiazepine, large intravenous overdoses have rarely caused signs in otherwise healthy people, although serious neurologic complications may occur in certain cases.
- Seizures: May be precipitated, particularly in susceptible patients.
- General toxicity: For any known or suspected overdose, consult a 24-hour poison information service that gives veterinary-specific advice.
- Management: If seizures occur, human reports describe management with barbiturates, phenytoin or high doses of benzodiazepines.
- Analeptic stimulants: In benzodiazepine overdose, analeptic stimulants such as caffeine and doxapram are generally not recommended.
Key Notes
Practical clinical points that support effective use of flumazenil in dogs and cats:
- Rapid onset: Clinical effects usually begin within 1 to 2 minutes of intravenous administration, but peak effect is not reached until 6 to 10 minutes.
- Short half-life: Duration of action is relatively brief (~1 hour), which may necessitate repeat dosing depending on the sedative used.
- Hepatic metabolism: Flumazenil is extensively metabolised by the liver. Human pharmacokinetic data indicate that liver dysfunction prolongs its half-life and effects without altering dosage requirements.
- Selective reversal: Reverses the sedative and amnestic effects of benzodiazepines; in people this happens without any change in benzodiazepine pharmacokinetics, so the benzodiazepine is still present and can re-sedate the patient as flumazenil wears off.
- Limited scope of action: Does not reverse non-benzodiazepine anesthetic components (e.g., tiletamine), which may influence recovery quality.
- Clinical setting use: Typically administered in a veterinary clinical setting rather than for at-home use.
- Injection only, human-labelled: Injection only, and human-labelled: there is no veterinary-licensed flumazenil product, and high first-pass metabolism means it cannot be given by mouth at all.
- Storage and dilution: Store at room temperature and protected from light; once drawn into a syringe or mixed with fluid, discard after 24 hours. It is physically compatible with lactated Ringer’s solution, 5% dextrose and normal saline.
