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There is no clinically significant drug interactions from coadministration of letrozole with cimetidine and warfarin. There is no evidence of clinically relevant interactions with other commonly prescribed drugs. There is no clinical experience on the use of letrozole in combination with other anticancer agents.
Letrozole inhibits in vitro the cytochrome P450-isozymes 2A6, and moderately 2C19. CYP2A6 does not play a major role in drug metabolism. Thus, clinically relevant interactions with CYP2C19 are unlikely to occur. However, caution should be used in the concomitant administration of drugs whose disposition is mainly dependent on these isoenzymes and whose therapeutic index is narrow.
Concurrent use of letrozole and tamoxifen may result in reduced letrozole serum concentrations.
