Pioglitazone shares a hepatic cytochrome metabolism pathway (CYP3A4 and CYP2C8) with ethinyl estradiol and norethindrone (CYP3A4), and reduces the bioavailability of certain oral contraceptives and their effectiveness. Higher dose oral contraceptive agents are required to overcome this effect in order to provide effective contraception. Rosiglitazone is metabolized by a separate cytochrome pathway (CYP2C8) that does not interfere with any oral contraceptive agents. The pharmacokinetics of rosiglitazone and pioglitazone are not affected by renal dysfunction and, therefore, do not require dose adjustments.
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