Oral contraception failure rate

Helms SE, Bredle DL, Zajic J, Jarjoura D, Brodell RT, Krishnarao I. Oral contraceptive failure rates and oral antibiotics, JAm Acad Dermatol (1997) 36,705-10. 

Like all women, older women who take oral contraceptives should take an oral contraceptive that contains the least amount of estrogen and progestin that is compatible with a low failure rate and individual patient needs. 

Oral contraceptive medications are among the most prescribed and effective drugs. The failure rates associated with various methods of contraception are cited in the following table. 

Before discussing the clinical application of these steroidal agents it is well to keep in mind the extraordinary efficacy of this mode of contraception. In Table I we present the data assembled by Venning (31) on the relative efficacy of various contraceptive methods. All of those studied in various experimental trials effectively reduced fertility, but the oral contraceptive most extensively studied (the norethynodrel-estrogen combination) is much the most effective. Indeed, the pregnancy rate listed appears to be attributable to failure to use the method properly rather than to a rare physiological exception to the action of the drug. 

Antiseizure therapy has importance implications for women s health. The efficacy of oral contraceptives is reduced by concomitant use of antiseizure drugs (failure rate of 3.1/100 years versus 0.7/100 years in nonepileptic controls) this may relate to the increased rate of oral contraceptive metabolism caused by antiseizure drugs that induce hepatic enzymes (Table 19-2) particular caution is needed with antiseizure drugs that induce CYP3A4. 

Although this advice has previously only been applied to broad-spectrum antibacterials that do not induce liver enzymes 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 penicillins. However, others contend that these instructions may confuse patients, and complicate pill taking, and could have the opposite effect of increasing the failure rate of oral contraceptives. ... 

Not established. The pharmaeokinetie and pharmacodynamic evidence in-dieates that eo-trimoxazole is not likely to reduce the effectiveness of combined oral eontraeeptives. Although there are a number of reports of contraceptive failure attributed to co-trimoxazole, these are anecdotal and unconfirmed, whereas the studies suggest increased contraceptive efficacy (but see below). It is possible that the cases are coincidental, and fit within the normal failure rate of combined oral contraceptives. The UK Family Planning Authority considered that it was almost certain that co-trimoxazole and sulphonamides did not interact with combined oral contraceptives. However, the Faculty of Family Planning and Reproductive Health Care (FFPRHC) Clinical Effectiveness Unit has issued guidance on the use of antibacterials with hormonal contraceptives. Although they recognise that there is poor evidence for contraceptive failure, they recommend that additional contraceptives, 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 co-trimoxazole, sulfonamides and trimethoprim. ... 

In a dermatological practice, of 124 women taking an oral contraceptive and antibacterials (mostly tetracyclines or erythromycin), 2 became pregnant, with a calculated failure rate of 1.2%. One patient was taking long-... 

The interactions between the oral contraceptives and tetracyclines summarised here are all that have been identified in the literature. Much of the evidence is anecdotal with insufficient controls (if any). These interactions are not adequately established and the whole issue remains controversial. Bearing in mind the extremely wide use of both drugs, any increase in the incidence of contraceptive failure above the accepted failure rate is clearly very low indeed. On the other hand, the personal and ethical consequences of an unwanted pregnancy can be very serious. For this reason, the Faculty of Family Planning and Reproductive Health Care (FFPRHC) Clinical Effectiveness Unit recommends that an additional form of contraception, such as condoms, should be used while taking a short course of antibacterials that do not induce liver eiKymes, and for 7 days after the antibacterial has been stopped. See Hormonal contraceptives + Antibacterials Penicillins , p.981, for more detailed information on how to manage this interaction. 

In the case of long-term use of tetracyclines for acne, at least 7 cases of contraceptive failure have been reported. Nevertheless, in statistical terms the only well-designed case-controlled study in dermatological practice indicated that the incidence of contraceptive failure due to this interaction could not be distinguished from the general and recognised failure rate of oral contraceptives. ... 

Smoking may increase the incidence of breakthrough bleeding. This may decrease the acceptability of the oral contraceptive, and lead to the use of less effective contraceptive methods. However, it also raises the question of whether smoking increases the failure rate of oral contraceptives. The only evidence that this may occur is anecdotal. Further study is needed. 

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