Interactions between somatropin and Chem mart tamoxifen (tamoxifen)
tamoxifen and somatropin (Moderate Drug-Drug)
GENERALLY AVOID: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of tamoxifen, which is metabolized by the isoenzyme. In ten healthy subjects, the potent CYP450 3A4 inducer rifampin (600 mg orally once a day for 5 days) decreased the peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and elimination half-life of tamoxifen (80 mg single oral dose) by 55%, 86% and 44%, respectively, compared to placebo. The AUC of the active N-demethyl metabolite decreased by 62% and Cmax increased by 46%, suggesting enhanced presystemic metabolism in the intestine. Aminoglutethimide has also been reported to significantly increase the clearance of tamoxifen by more than 3-fold. Coadministration of another CYP450 3A4 inducer, bexarotene, resulted in a 35% decrease in plasma concentrations of tamoxifen. The extent to which other CYP450 3A4 inducers may affect tamoxifen is unknown.
MANAGEMENT: In general, agents without CYP450 3A4-inducing activity are preferable in patients treated with tamoxifen, particularly if these agents are to be used for a prolonged period. Otherwise, pharmacologic response to tamoxifen should be monitored closely whenever an inducing agent is added to or withdrawn from therapy, and the tamoxifen dosage adjusted if necessary.
