Emergency hormonal contraceptives Antibacterials

Note that antibacterials that do not induce liver enzymes do not affeet the reliability of the progestogen-only contraceptives, see Progestogen-only contraceptives + Antibacterials, p.l007, or the progestogen-only emergency hormonal contraceptive, see Emergency hormonal contraceptives + Antibacterials , p.977. 

Levonorgestrel is metabolised to inactive substances before it is conjugated, and does not therefore undergo enterohepatic recycling of the active moiety. There is no reason to expect that its efficacy as an emergency contraceptive would be affected by antibacterials that alter gut flora and do not induce liver enzymes. No special precautions are necessary with these antibacterials. However, rifampicin and rifabutin are likely to reduce the efficacy of most forms of hormonal contraceptives, as they induce the metabolism of oestrogens and progestagens, see Hormonal contraceptives + Rifamycins , p. 1001. 

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