Contraception failure progestagen

VASODILATOR ANTIHYPERTENSIVES -BOSENTAN PROGESTOGENS 1 progesterone levels, which may lead to failure of contraception or poor response to treatment of menorrhagia Possibly induction of metabolism of progestagens Advise patients to use additional contraception for the period of intake and for 1 month after stopping co-administration with these drugs... 

Note that the mechanism behind the rare cases of failure of combined oral contraceptives seen with various broad-spectrum antibacterials is postulated to be reduced enterohepatic recycling of ethinylestradiol (see Hormonal contraceptives + Antibacterials Penicillins , p.981). Since progestagens are largely metabolised to inactive substances before they are conjugated, they do not undergo enterohepatic recycling of the active substance. 

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