Halothane
2-bromo-2-chloro-1,1,1-trifluoroethane
Also known as: Fluothane · Ineltano · phthorothanum · Halothanum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General Anesthesia | 3% (induction); 0.5-1.5% (maintenance) | Inhalation | Continuous | As needed for procedure | 🌎 NA |
| General Anesthesia | 0.5-3.5%, inhaled | Inhalation | Continuous | As needed for procedure | 🌎 NA |
| Induction of anaesthesia (unpremedicated) | 3-4% concentration | Inhalational | Continuous | Until induced | 🌍 EU |
| Maintenance of anaesthesia | 0.8-1.0% (MAC) | Inhalational | Continuous | Duration of procedure | 🌍 EU |
- General Anesthesia: Concentrations are dependent upon fresh gas flow rate.
- Induction of anaesthesia (unpremedicated): Delivered via calibrated vaporizer
- Maintenance of anaesthesia: Adjust according to individual requirement and concurrent drugs
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General Anesthesia | 3% (induction); 0.5-1.5% (maintenance) | Inhalation | Continuous | As needed for procedure | 🌎 NA |
| General Anesthesia | 0.5-3.5%, inhaled | Inhalation | Continuous | As needed for procedure | 🌎 NA |
| Induction of anaesthesia (unpremedicated) | 3-4% concentration | Inhalational | Continuous | Until induced | 🌍 EU |
| Maintenance of anaesthesia | 0.8-1.0% (MAC) | Inhalational | Continuous | Duration of procedure | 🌍 EU |
- General Anesthesia: Concentrations are dependent upon fresh gas flow rate.
- Induction of anaesthesia (unpremedicated): Delivered via calibrated vaporizer
- Maintenance of anaesthesia: Adjust according to individual requirement and concurrent drugs
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General Anesthesia (Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas) | Induction: 2%-4%, maintenance: 0.25%-2% | Inhalation | Continuous | As needed for procedure | 🌎 NA |
- General Anesthesia (Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas): Using a non-rebreathing system.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General Anesthesia | 2% (small birds) or 2.5%-3% (large birds) for induction; 0.5%-1.5% for maintenance | Inhalation | Continuous | As needed for procedure | 🌎 NA |
- General Anesthesia: Induction usually occurs in 2-4 minutes. Recovery takes 3-5 minutes. Bradycardia, hypotension, and hypothermia may occur but rapidly resolve upon discontinuation.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General Anesthesia (Draft Horses) | 4%-5% initially, maintenance 2.5%-3% | Inhalation | Continuous | As needed for procedure | 🌎 NA |
- General Anesthesia (Draft Horses): Administered in an oxygen-enriched semi-closed large animal circle system. Reduce as indicated by physical monitoring.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Halothane is a classic halogenated inhalant general anesthetic that was historically a mainstay in veterinary medicine due to its potency, controllability, and non-flammability.
While it paved the way for modern veterinary anesthesia, it is largely obsolete and no longer commercially available in many countries. It has been widely replaced by newer agents (such as isoflurane, sevoflurane, and desflurane) which offer superior safety profiles, particularly regarding cardiovascular depression and hepatotoxicity.
Clinical Pearls:
- Halothane has a higher blood-gas partition coefficient compared to modern inhalants, leading to slower induction and recovery times.
- It is uniquely known for sensitizing the myocardium to catecholamines, significantly increasing the risk of ventricular arrhythmias.
- Approximately 12% of the drug undergoes hepatic metabolism (unlike isoflurane which is <1%), contributing to its potential for immune-mediated hepatotoxicity (halothane hepatitis).
Mechanism of action
The exact mechanism of inhalant anesthetics remains incompletely understood, but involves multiple central nervous system targets:
- Lipid Matrix Interaction: Historically explained by the Meyer-Overton rule, halothane interacts with the lipid bilayer of neuronal membranes, disrupting normal ion channel function.
- Receptor Modulation: Modern evidence suggests halothane acts via positive allosteric modulation of inhibitory receptors (such as GABA_A and glycine receptors) → enhancing CNS depression.
- Excitatory Inhibition: It simultaneously inhibits excitatory receptors (such as NMDA and nicotinic acetylcholine receptors) → dampening neuronal excitability.
Systemic Effects:
- Profound CNS depression and blunting of thermoregulatory centers.
- Increased cerebral blood flow.
- Dose-dependent respiratory depression (especially pronounced in ruminants).
- Significant myocardial depression, vasodilation, and hypotension.
Safety & warnings
Contraindications
- History or predilection towards malignant hyperthermia
- Significant hepatotoxicity or unexplained fever/jaundice after previous halothane exposure
- Liver disease
- Patients with a history of malignant hyperthermia
Adverse effects
- Dose-related hypotension
- Cardiac depression and decreased cardiac output
- Cardiac dysrhythmias (sensitizes myocardium to catecholamines)
- Malignant hyperthermia-stress syndrome (reported in pigs, horses, dogs, cats)
- Hepatotoxicity (jaundice, fatal liver necrosis)
- Respiratory depression
- Hypothermia
- Dose-dependent hypotension
- Bradycardia
- Decreased myocardial contractility
- Reduced hepatic blood flow
- Ventricular arrhythmias
- Neonatal depression (crosses placental barrier)
Precautions
Hepatotoxicity Warning: Halothane can cause severe, sometimes fatal, liver necrosis. Do not re-expose patients who have previously shown unexplained fever or jaundice following halothane anesthesia.
- Cardiovascular/Neurologic: Use with extreme caution in patients with cardiac arrhythmias, hepatic impairment, increased intracranial pressure (CSF) or head injury, myasthenia gravis, or pheochromocytoma.
- Pregnancy: Categorized as Class C. May be teratogenic; use only when benefits clearly outweigh potential risks.
- Equipment: Halothane vapor can react with aluminum, brass, and lead in the presence of moisture. It also causes rapid deterioration of rubber and some plastics.
Drug interactions
Not recommended for post-operative analgesia in patients that have received halothane anesthesia due to increased risk of hepatotoxicity.
Can decrease requirements of halothane by up to 40%.
Use with caution; additive neuromuscular blockade may occur.
Use with caution; additive neuromuscular blockade may occur.
Additive neuromuscular blockade may occur.
May induce increased incidences of cardiac effects (bradycardia, arrhythmias, sinus arrest, apnea) and malignant hyperthermia in susceptible patients.
Halothane sensitizes the myocardium to catecholamines; severe ventricular arrhythmias may result. Use with extreme caution at reduced doses.
May cause significant hypotension if used with halothane.
Reduces the concentration of halothane required to achieve surgical anaesthesia
Reduces the concentration of halothane required to achieve surgical anaesthesia
Reduces the concentration of halothane required to achieve surgical anaesthesia
Facilitates the generation of ventricular arrhythmias
Monitoring
- Respiratory and ventilatory status
- Cardiac rate and rhythm (ECG is highly recommended due to arrhythmogenic potential)
- Blood pressure (especially in 'at risk' patients)
- Level of anesthetic depth
- Body temperature (monitor for hypothermia or malignant hyperthermia)
- Heart rate and rhythm (ECG)
- Respiratory rate and depth
- Capnography (ETCO2)
- Anaesthetic depth (jaw tone, palpebral reflex)
Pharmacokinetics
Absorption
Rapidly absorbed through the lungs into the systemic circulation.
Distribution
Highly lipid soluble; distributes widely into tissues including the CNS. Distributed into milk.
Metabolism
Approximately 12% of the absorbed drug is metabolized by the liver to trifluoroacetic acid, chlorine, and bromine radicals.
Elimination
The bulk of the absorbed drug is re-excreted by the lungs and eliminated with expired air. Hepatic metabolites are excreted in the urine.
Overdose
Overdosage of halothane results in profound cardiopulmonary depression, characterized by severe hypotension, bradycardia, arrhythmias, and apnea.
Treatment:
- Immediately turn off the anesthetic vaporizer.
- Flush the breathing circuit with 100% oxygen.
- Institute positive pressure ventilation.
- Provide cardiovascular support (e.g., IV fluid volume expansion, positive inotropes like dobutamine, and anticholinergics for bradycardia).
- Lidocaine may be required to treat halothane-induced ventricular dysrhythmias.
Available products
Formulations
- Inhalation liquid (vaporized for administration)
- Inhalational liquid: 250 ml bottle
Veterinary
- Fluothane 250 ml bottle
- Halothane POM-V 250 ml bottle
Regulatory status
POM-V classification.
POM-V classification.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store below 40°C in a tight, light-resistant container. Halothane stability is maintained by the addition of thymol and ammonia. Thymol does not vaporize and may accumulate in the vaporizer, causing a yellow discoloration (do not use discolored solutions). In the presence of moisture, halothane vapor reacts with aluminum, brass, and lead. It also causes rapid deterioration of rubber and some plastics.
Client information
Halothane is an inhaled anesthetic gas used to keep animals unconscious and pain-free during surgery.
- Modern Use: While it was very common in the past, veterinary hospitals today mostly use newer, safer anesthetic gases. If halothane is used, your veterinarian has determined it is appropriate for your pet's specific situation.
- Risks: Like all general anesthetics, it carries risks such as drops in blood pressure, changes in heart rhythm, and lowered body temperature. Your veterinary team will closely monitor your pet's vital signs throughout the procedure.
- Post-Anesthesia: Your pet may be groggy or sleepy for a day or two after coming home. Keep them in a warm, quiet, and safe environment while they recover.
- Warning: Inform your veterinarian if your pet has ever had a bad reaction to anesthesia in the past, particularly unexplained fevers or liver issues.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.