Liver enzymes elevation due to concurrent dexamethasone and lapatinib: Clinical and in vitro evidence.

e13023 Background: Concomitant usage of lapatinib (L) and dexamethasone (D), which are cytochrome P450 (CYP) 3A4 substrate and inducer respectively, may increase the formation of potentially hepatotoxic reactive L metabolites. This study aims to evaluate the effect of D on the occurrence of liver enzyme elevation and to ascertain its role using a parallel in vitro experiment. Methods: Clinical effects of D on L-induced liver enzyme elevation were evaluated in a nested case-control study. Liver enzyme elevation is defined as the first clinically significant change (from baseline) of either total bilirubin (TB), alanine aminotransferase (ALT) or aspartate aminotransferase (AST) by at least 1 grade, based on the Common Terminology Criteria for Adverse Events (CTCAE) version 4.02. In the in vitro study, metabolically-competent transforming growth factor α mouse hepatocytes (TAMH) cells were treated with L and viabilities were compared in the presence or absence of D. Results: Among 97 patients, liver enzyme e...