Halothane (Molecule of the Month for June 2007)
Halothane is used as a general anaesthetic. It 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.
Repeated exposure to halothane in adults was noted in rare cases to result in severe liver injury. This occurred in about 1 in 35,000 exposures. The resulting syndrome was referred to as halothane hepatitis, and is thought to result from the metabolism of halothane to trifluoroacetic acid via oxidative reactions in the liver. Concern for hepatitis resulted in a dramatic reduction in the use of halothane for adults. It was replaced in the 1980s by enflurane and isoflurane. By the year 2005 the common volatile anaesthetics in use were isoflurane, sevoflurane, and desflurane. Since the risk of halothane hepatitis in children was substantially lower than in adults, halothane saw continued use in pediatrics in the 1990s. However, by the year 2000 sevoflurane had largely replaced the use of halothane in children.
All volatile anaesthetics such as halothane can trigger malignant hyperthermia in genetically susceptible individuals. The caffeine-halothane contracture test was developed to directly test muscle biopsy specimens for this susceptibility. This test may be replaced by genetic testing in the future.
Formal Chemical Name (IUPAC)
Update by Karl Harrison
(Molecule of the Month for June 2007 )