The effect of ketoconazole and diltiazem on oestrogen metabolism in postmenopausal women after single dose oestradiol treatment

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AimsThe effect of the CYP3A4 inhibitors ketoconazole and diltiazem on the pharmacokinetics of oestrone was studied in six healthy postmenopausal women after treatment with a single oral dose of oestradiol.MethodsPlasma oestrone concentrations were measured following the administration of 1) oestradiol, 2) oestradiol and ketoconazole and 3) oestradiol and diltiazem.ResultsTreatment with ketoconazole increased the AUC of oestrone (+ 4029 nmol l−1 h; 95% CI on the difference: 1588, 6471) and its Cmax (+ 306 nmol l−1; 95% CI on the difference: 117, 496). The AUC and Cmax of oestrone tended to increase on treatment with diltiazem although this did not reach the level of statistical significance.ConclusionsThe small increase in the plasma concentrations of oestrone formed from 17β-oestradiol during co-administration with ketoconazole is unlikely to be clinically significant.

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