Estradiol CYP3A4/5/7 substrate

Because nevirapine induces CYP3A4, this drug may lower plasma concentrations of coadministered CYP3A4 substrates. Methadone withdrawal has been reported in patients receiving nevirapine, presumably as a consequence of enhanced methadone clearance. Plasma ethinyl estradiol and norethindrone concentrations decrease by 20% with nevirapine, and alternative methods of birth control are advised. Nevirapine also can reduce concentrations of some coadministered HIV protease inhibitors. 

Yang B-B, Siedlik PH, Smilhers JA, Sedman AJ, Stem RH. Atorvastatin pharmacokinetic interactions with other CYP3A4 substrates erythromycin and ethinyl estradiol. Pharm Res ( 996) 13 (9 Suppl), S-437. 

The available case reports in the FDA AERS support the published literature that there are pharmacokinetic interactions between St. John s wort and CYP3A4 and/or p-glycoprotein substrates, such as cyclosporine, levonorgestrel/estradiol and sildenafil, and pharmacodynamic interactions with the SSRIs or MAOI. Subsequent clinical studies including those conducted via a CDER clinical pharmacology research cooperative agreement (14—16) provided mechanistic basis of many of these interactions (refer to Chapter 4). 

CICLOSPORIN OESTROGENS Possibly t plasma concentrations of cidosporin Estradiol and immunosuppressants are substrates of CYP3A4 and P-gp. Estradiol is an inhibitor of P-gp Monitor blood cidosporin concentrations. Monitor renal fundion prior to concurrent therapy. Be aware that infections in immunocompromised patients carry a serious threat to life... 

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