Oral contraceptive penicillin effects

The effects of the progestins are decreased when administered with anticonvulsants, barbiturates, or rifampin. Administration of the penicillins or tetracyclines with the oral contraceptives decreases the effects of the oral contraceptives. 

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. ... 

The pharmacokinetics of a single 25-mg dose of doxylamine in 13 subjeets and the pharmacokinetics of a single 50-mg dose of diphenhydramine in 10 subjeets were not significantly altered by the use of low-dose eombined oral eontraceptives. Cases of oral contraceptive failure have been attributed to the use of doxylamine, chlorpheniramine, and an unnamed antihistamine, but these antihistamines were all used in con-junetion with penieillins, which would seem to be a more likely cause of contraceptive failure (see Hormonal contraceptives + Antibacterials Penicillins , p.981). The effect of the antihistamines on the pharmacokinetics and pharmacodynamics of contraceptive steroids appear not to have been studi. No particular precautions would seem necessary during concurrent use. 

Sulfasalazine can inhibit the absorption of cardiac glycosides and folic acid. It may displace certain drugs, including warfarin, phenytoin, methotrexate, tolbutamide, chlorpropamide, and oral sulfonylureas, from their protein binding sites. Sulfasalazine can diminish the effectiveness of penicillins and estrogen-containing oral contraceptives. 

Certain concomitantly administered drugs may interfere with the effectiveness of the oral contraceptives or lead to an increased incidence of breakthrough bleeding. These include rifampin, isoniazid, ampiciUin, neomycin, penicillin V, chloramphenicol, sulfonamides, nitrofurantoin, phenytoin, barbiturates, primidone, analgesics, and phenothiazines. 

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. ... 

Absorption - use of broad-spectrum antibiotics (e.g. penicillin) may, through an effect of bacterial flora in the gut, result in reduced absorption and effectiveness of oral contraceptives. 

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