<p>No formal drug-drug interaction studies with trastuzumab emtansine in humans have been conducted. In vitro metabolism studies in human liver microsomes suggest that DM1, a component of trastuzumab emtansine, is metabolized mainly by CYP3A4 and, to a lesser extent, by CYP3A5. DM1 does not induce or inhibit P450-mediated metabolism in vitro. Caution should be taken when trastuzumab emtansine is co-administered with potent CYP3A inhibitors.</p>