Halothane Toxicity

"Few drugs have excited such widespread interest and stimulated as much clinical and laboratory investigation as halothane." —Editorial, Brit. J. Anaesth. (1962).[1] Halothane is a clear, heavy, and colorless liquid with a sweet and non-irritating odor. Halothane’s structure is that of an alkane. It has primarily been used clinically as an inhalational anesthetic. Ether and Chloroform were rapidly replaced by halothane upon its introduction in 1956. Halothane is associated with a lower risk of nausea and vomiting than the fluorinated methyl ethyl ether agents.[2] Due to its favorable side effect profile, halothane became the standard of practice, used in almost every operating room and for the comparison of other inhalational anesthetics as they came to the market. Although halothane has several drawbacks, the lack of flammability and general smoothness of administration led to rapid, widespread use, which only changed with the growing popularity of sevoflurane in the 1990s.[3] Although widely replaced by isoflurane or sevoflurane, halothane is the last common non-ether anesthetic used in the operating room. Halothane is the most soluble of the currently used anesthetic agents, indicating that the equilibration of inspired/brain partial pressures is the greatest. Although this property would seem to improve the safety profile of halothane, halothane is also the most potent of the inhalational anesthetics.[4][5] Cardiorespiratory instability (i.e., hypotension, bradycardia), sensitizing the myocardium to catecholamine-induced arrhythmias, and mild liver dysfunction are relatively common side effects of halothane. Arrhythmias are especially common in neonates and children after the administration of halothane, particularly bradyarrhythmias.[6] Additional adverse effects of halothane include hepatotoxicity (type 1) and hepatitis (type 2), which will be the focus of this activity. Type 1 hepatotoxicity is a transient, benign liver injury that is self-limiting; this differs from Type 2 hepatotoxicity, which is fulminant liver damage that can lead to liver failure, associated with a high mortality rate.