Several clinical studies strongly suggest that obese patients could be particularly at risk for halothane and isoflurane-induced acute hepatotoxicity [18,59-63]. This is probably because obesity is often associated with higher hepatic CYP2E1 activity, which generates greater levels of the toxic acyl chloride metabolites. However, some obese individuals do not present high CYP2E1 activity and thus they may not be at risk for halothane and isoflurane-induced liver injury. This evidence concerns the gene CYP2E1 and obesity due to melanocortin 4 receptor deficiency.