Preliminary results of a clinical drug-drug interaction study, examining the effect of ganetespib on the pharmacokinetics of the CYP2C19-sensitive probe omeprazole,show a modest (20%) increase in omeprazole exposure when coadministered with ganetespib. In vitro data implies expectation of greater interaction with CYP2C19substrates than with CYP3A4 substrates. Caution is advised when sensitive narrow therapeutic range CYP3A4 or CYP2C19 substrates are concomitantly administered.