Volatile metabolites of halothane in the rabbit

To date, carbon dioxide is the only volatile metabolite that has been identified to result from the biotransformation of halothane. This study was undertaken to determine whether other volatile metabolites might be formed. Expiratory gas from four rabbits given halothane by inhalation and from three rabbits into which the halothane was injected intraperitoneally was analyzed by gas chromatography. Qualitative analysis of the metabolites was made by injecting 50-70 microliter of the expired halothane condensed in an ultralow-temperature device (-80 C) attached to the mass spectrometer. Gas chromatography revealed two volatile metabolites between the air peak and the halothane peak. They were identified by mass spectra to be CF2:CHCl and CF2CH2Cl. These volatile metabolites appeared immediately after the beginning of anesthesia. The present investigation suggests the possible existence of a previously unknown metabolic pathway of defluorination and debromination occurring in the early stage of halothane biotransformation. These volatile metabolites may be toxic, highly reactive intermediates that undergo further biotransformation.