Percentage of Halothane metabolized -

The extent and location of inhaled anesthetic metabolism depends on multiple chemical factors. Inhaled anesthetics undergo varying degrees of biotransformation in various tissues. Methoxyflurane undergoes by far the greatest metabolism, estimated at 70%, and experiments indicate that only a small fraction of drug taken up into body tissues is exhaled. Given the remarkable lipophilicity of methoxyflurane, respiratory clearance of this drug from muscle and fat extends over a period of days. Halothane is the next most lipophilic drug and ranks second in metabolic clearance. Thus, prolonged residence in body tissues is an impoant factor in the biotransformation of inhaled anesthetics. Chemical stability is another impoant factor. Of the major organs involved in anesthetic biotransformation, the liver and kidneys are exposed to the highest metabolite concentrations and thus are most susceptible to damage from toxic metabolites. Clinically significant hepatotoxicity is primarily associated with exposure to halothane, and nephrotoxicity is associated with methoxyflurane. Ref: Miller's anesthesia 8th edition