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| Trade names | Fluothane, Somnothane, Rhodialothan |
| AHFS/Drugs.com | FDA Professional Drug Information |
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| Routes of administration | Inhalation |
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| Metabolism | Hepatic (CYP2E1[4]) |
| Excretion | Kidney,respiratory |
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| ECHA InfoCard | 100.005.270 |
| Chemical and physical data | |
| Formula | C2HBrClF3 |
| Molar mass | 197.38 g·mol−1 |
| 3D model (JSmol) | |
| Density | 1.871 g/cm3 (at 20 °C) |
| Melting point | −118 °C (−180 °F) |
| Boiling point | 50.2 °C (122.4 °F) |
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Halothane (Bromochlorotrifluoroethane), sold under the brand nameFluothane among others, is ahalocarbon with thechemical formulaCF3CHBrCl. It is used as ageneral anaesthetic given byinhalation. It can be used to induce or maintainanaesthesia.[5] Its use indeveloped countries has been mostly replaced by newer anesthetic agents such assevoflurane.[6] One of its benefits is that it does not increase the production ofsaliva, which can be particularly useful in those who are difficult tointubate.[5]
Side effects include anirregular heartbeat,respiratory depression, andhepatotoxicity.[5] Like all volatile anesthetics, it should not be used in people with a personal or family history ofmalignant hyperthermia.[5] It appears to be safe inporphyria.[7] It is unclear whether its usage duringpregnancy is harmful to the fetus, and its use during aC-section is generally discouraged.[8] Halothane is achiral molecule that is used as aracemic mixture.[9]
Halothane was discovered in 1951.[10] It was approved for medical use in the United States in 1958.[3] It was removed from theWorld Health Organization's List of Essential Medicines in 2025.[11] It is not available in the United States.[8] Halothane may contribute toozone depletion.[12][13]
It is a potent anesthetic with aminimum alveolar concentration (MAC) of 0.74%.[14] Itsblood/gas partition coefficient of 2.4 makes it an agent with moderate induction and recovery time.[15] It is not a goodanalgesic and its muscle relaxation effect is moderate.[16]
Halothane is colour-coded red onanaesthetic vaporisers.[17]
Side effects includeirregular heartbeat,respiratory depression, andhepatotoxicity.[5] It appears to be safe inporphyria.[7] It is unclear whether use duringpregnancy is harmful to the baby, and it is not generally recommended for use during aC-section.[8]In rare cases, repeated exposure to halothane in adults was noted to result in severeliver injury. This occurred in about one in 10,000 exposures. The resulting syndrome was referred to as halothanehepatitis, immunoallergic in origin,[18] and is thought to result from the metabolism of halothane totrifluoroacetic acid via oxidative reactions in the liver. About 20% of inhaled halothane is metabolized by the liver and these products are excreted in the urine. The hepatitis syndrome had a mortality rate of 30% to 70%.[19] Concern for hepatitis resulted in a dramatic reduction in the use of halothane for adults and it was replaced in the 1980s byenflurane andisoflurane.[20][21] By 2005, the most common volatile anesthetics used wereisoflurane,sevoflurane, anddesflurane. Since the risk of halothane hepatitis in children was substantially lower than in adults, halothane continued to be used in pediatrics in the 1990s as it was especially useful for inhalation induction of anesthesia.[22][23] However, by 2000, sevoflurane, excellent for inhalation induction, had largely replaced the use of halothane in children.[24]
Halothane sensitises the heart to catecholamines, so it is liable to cause cardiac arrhythmia, occasionally fatal, particularly ifhypercapnia has been allowed to develop. This seems to be especially problematic in dental anesthesia.[25]
Like all the potent inhalational anaesthetic agents, it is a potent trigger formalignant hyperthermia.[5] Similarly, in common with the other potent inhalational agents, it relaxes uterine smooth muscle and this may increase blood loss during delivery or termination of pregnancy.[26]
People can be exposed to halothane in the workplace by breathing it in as waste anaesthetic gas, skin contact, eye contact, or swallowing it.[27] TheNational Institute for Occupational Safety and Health (NIOSH) has set arecommended exposure limit (REL) of 2 ppm (16.2 mg/m3) over 60 minutes.[28]
The exact mechanism of the action of general anaestheticshas not been delineated.[29] Halothane activatesGABAA andglycine receptors.[30][31] It also acts as anNMDA receptor antagonist,[31] inhibitsnACh andvoltage-gated sodium channels,[30][32] and activates5-HT3 andtwin-pore K+ channels.[30][33] It does not affect theAMPA orkainate receptors.[31]
Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is a very dense, highly volatile, clear, colourless, nonflammable liquid with achloroform-like sweet odour. It is very slightly soluble in water and miscible with various organic solvents. Halothane can decompose tohydrogen fluoride,hydrogen chloride andhydrogen bromide in the presence of light and heat.[34]
| Boiling point: | 50.2 °C | (at 101.325 kPa) |
| Density: | 1.871 g/cm3 | (at 20 °C) |
| Molecular Weight: | 197.4 Da | |
| Vapor pressure: | 244 mmHg (32 kPa) | (at 20 °C) |
| 288 mmHg (38 kPa) | (at 24 °C) | |
| MAC: | 0.75 | vol % |
| Blood:gas partition coefficient: | 2.3 | |
| Oil:gas partition coefficient: | 224 |
Chemically, halothane is analkyl halide (not anether like many other anesthetics).[4] The structure has one stereocenter, so (R)- and (S)-optical isomers occur.[citation needed]
The commercial synthesis of halothane starts fromtrichloroethylene, which is reacted withhydrogen fluoride in the presence ofantimony trichloride at 130 °C to form2-chloro-1,1,1-trifluoroethane. This is then reacted withbromine at 450 °C to produce halothane.[35]
Attempts to find anesthetics with less metabolism led tohalogenated ethers such asenflurane andisoflurane. The incidence ofhepatic reactions with these agents is lower. The exact degree ofhepatotoxic potential of enflurane is debated, although it is minimally metabolized. Isoflurane is essentially not metabolized and reports of associated liver injury are quite rare.[36] Small amounts oftrifluoroacetic acid can be formed from both halothane and isoflurane metabolism and possibly accounts for cross sensitization of patients between these agents.[37][38]
The main advantage of the more modern agents is lower blood solubility, resulting in faster induction of and recovery from anaesthesia.[39]
Halothane was first synthesized byC. W. Suckling ofImperial Chemical Industries in 1951 at the ICIWidnes Laboratory and was first used clinically by M. Johnstone inManchester in 1956. Initially, many pharmacologists and anaesthesiologists had doubts about the safety and efficacy of the new drug. But halothane, which required specialist knowledge and technologies for safe administration, also afforded British anaesthesiologists the opportunity to remake their speciality as a profession during a period, when the newly establishedNational Health Service needed more specialist consultants.[40] In this context, halothane eventually became popular as a nonflammable general anesthetic replacing othervolatile anesthetics such astrichloroethylene,diethyl ether andcyclopropane. In many parts of the world it has been largely replaced by newer agents since the 1980s but is still widely used in developing countries because of its lower cost.[41]
Halothane was given to many millions of people worldwide from its introduction in 1956 through the 1980s.[42] Its properties include cardiac depression at high levels, cardiac sensitization tocatecholamines such asnorepinephrine, and potent bronchial relaxation. Its lack of airway irritation made it a common inhalation induction agent in pediatric anesthesia.[43][44] Its use indeveloped countries has been mostly replaced by newer anesthetic agents such assevoflurane.[45] It is not commercially available in the United States.[8]
Halothane is available as a volatile liquid, at 30, 50, 200, and 250 ml per container but in many developed nations is not available having been displaced by newer agents.[46]
 | This article needs to beupdated. Please help update this article to reflect recent events or newly available information.(October 2025) |
It is the onlyinhalational anesthetic containingbromine, which makes itradiopaque.[47] It is colorless and pleasant-smelling, but unstable in light. It is packaged in dark-colored bottles and contains 0.01%thymol as a stabilizing agent.[20]
Owing to the presence of covalently bonded fluorine, halothane absorbs in theatmospheric window and is therefore agreenhouse gas. However, it is much less potent than most otherchlorofluorocarbons andbromofluorocarbons due to its short atmospheric lifetime, estimated at only one year vis-à-vis over 100 years for manyperfluorocarbons.[48] Despite its short lifespan, halothane still has aglobal warming potential 50 times that of carbon dioxide, although this is over 100 times smaller than the most abundant fluorinated gases, and about 800 times smaller than the GWP ofsulfur hexafluoride over 500 years.[49] Halothane is believed to make a negligible contribution toglobal warming.[48]
Halothane is anozone depleting substance with anODP of 1.56 and it is calculated to be responsible for 1% of total stratospheric ozone layer depletion.[12][13] Unlike most ozone depleting substances, it is not governed under theMontreal Protocol.[50]
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