Halothane

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Halothane vapour (trademarked as Fluothane) is an inhalational general anaesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anaesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and chlorine atoms present in halothane. It is colourless and pleasant-smelling, but unstable in light. It is packaged in dark-coloured bottles and contains 0.01% thymol as a stabilising agent. Halothane is a core medicine in the World Health Organization's "Essential Drugs List", which is a list of minimum medical needs for a basic health care system.[2] Its use in developed countries however has almost entirely been superseded by newer inhalational anaesthetic agents.

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Related substances

Chemically, halothane is not an ether; it is an alkane. The structure has one stereocentre, so there are (R) and (S) optical isomers. Attempts to find anaesthetics with less metabolism led to halogenated ethers such as enflurane and isoflurane. The incidence of hepatic reactions with these agents is lower. The exact degree of hepatotoxic potential of enflurane is debated, although it is minimally metabolised. Isoflurane is essentially not metabolised and reports of associated liver injury are quite rare. Small amounts of trifluoroacetic acid can be formed from both halothane and isoflurane metabolism and possibly accounts for cross sensitisation of patients between these agents.

History

This halogenated hydrocarbon was first synthesised by C. W. Suckling of Imperial Chemical Industries (ICI) in 1951 and was first used clinically by M. Johnstone in Manchester in 1956. Halothane became popular as a nonflammable general anaesthetic replacing other volatile anaesthetics such as diethyl ether and cyclopropane. Use of the anesthetic was phased out during the 1980s and 1990s as newer anesthetic agents became popular. Halothane retains some use in veterinary surgery and in the Third World because of its lower cost.

Halothane was given to many millions of adult and pediatric patients worldwide from its introduction in 1956 through the 1980s. Its properties include cardiac depression at high levels, cardiac sensitisation to catecholamines such as norepinephrine, and potent bronchial relaxation. Its lack of airway irritation made it a common inhalation induction agent in pediatric anaesthesia. Due to its cardiac depressive effect, it was contraindicated in patients with cardiac failure. Halothane was also contraindicated in patients susceptible to cardiac arrhythmias, or in situations related to high catecholamine levels such as pheochromocytoma.

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