Combined oral contraceptive failure

A few anecdotal cases of combined oral contraceptive failure have been reported with cefalexin, cefalexin with clindamycin, and unspecified cephalosporins. The interaction (if such it is) appears to be very rare indeed. 

One or two cases of combined oral contraceptive failure have been reported in patients given chloramphenicol, clindamycin (used with cefalexin), daps one, fus idic acid, isoniazid, nifurtoinol and nitrofurantoin. Thes e is olated cas e are anecdotal and unconfirmed, and the interaction (if s uch it is) appears to be very rare indeed. The combination of aminosalicylic acid, isoniazid and streptomycin does not appear to affect contraceptive efficacy. 

Combined oral contraceptive failure has been attributed to amp-icillin, amoxicillin, flucloxacillin, oxacillin, phenoxymethylpeni-cillin, pivampicillin and talampicillin. However, the interaction (if such it is), appears to be veiy rare. Controlled studies have not shown any effect of ampicillin on contraceptive steroid levels and ovarian suppression. 

St John s wort may affect the pharmacokinetics of desogestrel, ethinylestradiol, and norethisterone. Both breakthrough bleeding and, more rarely, combined oral contraceptive failure have been reported in women taking St John s wort Two cases describe the failure of emergency hormonal contraception, which was attributed to the use of St John s wort... 

Thus, contraceptive counseling should be an integrated part of the preconceptional care for all women with diabetes and is described in detail in two recent reviews [37,38]. In essence, barrier methods are well suited for the well-motivated couple, but when an increased risk of user s failure can be predicted, intrauterine devices or combined oral contraceptives may be the only acceptable reversible alternative. Intrauterine devices are very efficient and without metabolic side effects and can be used on the same indications and with the same reservations as in nondiabetic women. Intrauterine devices are therefore well suited for women with diabetes, especially parous women. 

Co-cyprindiol is expected to interact with enzyme inducers in a similar manner to the combined oral contraceptives, and therefore the risk of contraceptive failure is increased. Like combined oral contraceptives, there may be rare cases of contraceptive failure with broad-spectrum antibacterials. There is some evidence that co-cyprindiol also interacts with minocycline to increase facial pigmentation. 

The interaction between metronidazole and combined oral contraceptives is not established, and the whole issue of any interaction with broad-spectrum antibacterials remains very controversial. Bearing in mind the extremely wide use of both metronidazole and combined oral contraceptives, any increased incidence of contraceptive failure above that seen in general usage is clearly very low indeed. The Faculty of Family Planning and Reproductive Health Care (FFPRHC) Clinical Effectiveness Unit has issued guidance on the use of antibacterials with combined hormonal contraceptives. Although they recognise that there is poor evidence for contraceptive failure, they recommend that additional form of contraception, such as condoms, should be used for short courses of antibacterials, see Hormonal contraceptives + Antibacterials Penicillins , p.981, for more detailed information. This applies to both the oral and the patch form of the combined contraceptive. This advice has usually been applied to only broad-spectrum antibacterials that do not induce liver enzymes but the FFPRHC notes that some confusion has occurred over which antibacterials are considered to be broad-spectrum , and thus they recommend that this advice is applied to all antibacterials that do not induce liver enzymes, which would include metronidazole. ... 

Ciprofloxacin, moxifioxacin and ofloxacin have been shown not to affect the pharmacokinetics of combined oral contraceptives in controiied studies. No cases of contraceptive failure appear to have been reported, and ovarian suppression is not affected. The piasma ieveis of moxifioxacin may be modestly reduced by combined orai contraceptives. 

One woman taking a combined oral contraceptive is briefly reported to have shown breakthrough bleeding and to have become pregnant while taking sulfamethoxypyridazine." " One case of a pregnancy, in a woman who had taken a sulphonamide (unspecified) and an oral contraceptive (unspecified), was identified in the adverse reactions register of the CSM in the UK for the years 1968 to 1984 (a total of 62 cases were attributed to other antibacterials). Three further cases of failure have been attributed to the use of sulfafurazole (sulfisoxazole) and a sulphonamide (unspecified). ... 

A study in 10 HIV-positive women found that nevirapine 200 mg once daily for 2 weeks then twice daily for a further 2 weeks decreased the median AUC and elimination half-life of ethinylestradiol by 29% and 31%, respectively, and decreased the median AUC of norethisterone by 19%. The women received two single doses ofa combined oral contraceptive (ethinylestradiol/norethisterone 35 micrograms/1 mg) 2 days before the nevirapine and on the last day of the nevirapine. Nevirapine was added to established antiretroviral therMy (commonly 3 drugs), which had been unchanged for at least 4 weeks. A retrospective study identified 22 women who were prescribed oral eontraceptives and also reeeived an NNRTl. None of the 6 women taking nevirapine experienced contraceptive failure. However, medication adherence could not be confirmed. ... 

The manufacturer hriefly notes that no clinically significant interaction was seen between indinavir and a combined oral contraceptive eontaining ethinylestradiol and norethisterone. In a retrospective study there were no reports of contraceptive failure in 9 patients taking indinavir (overall... 

The manufacturer briefly notes that in women taking a combined oral contraceptive (ethinylestradiol/norethisterone 35/400 micrograms) nelfinavir 750 mg three times daily for one week decreased the AUCs of ethi-nylestradiol and norethisterone by 47% and 18%, respectively. In a retrospective study 7 of 21 women taking nelfinavir experienced contraceptive failure (overall there were 8 contraceptive failures out of 33 women taking protease inhibitors). However, medication adherence could not be confirmed. ... 

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