OBJECT DRUGS

• Contraceptives, Oral

PRECIPITANT DRUGS

Antibiotics, Oral:

• Amoxicillin (Amoxil, etc.)
• Ampicillin
• Tetracyclines
• Other Oral Antibiotics

Comment:

(See Contraceptives, Oral + Enzyme Inducers for rifabutin, rifapentine, and rifampin). Menstrual irregularities and (rarely) unintended pregnancies have occurred during or after oral antibiotic therapy in women on oral contraceptives. The antibiotics most often implicated are ampicillin (and related penicillins) and tetracyclines, but isolated cases have occurred with many antibiotics. This interaction is controversial; evidence supporting the interaction is largely anecdotal, but most negative studies are also flawed. Although a causal relationship has not been established, assume that the interaction occurs until proven otherwise. Theoretically antibiotics that inhibit CYP3A4 (e.g., erythromycin or clarithromycin) would inhibit estrogen and progestin metabolism, thus decreasing the likelihood of reduced contraceptive efficacy.

Class 3: Assess Risk & Take Action if Necessary

• Circumvent/Minimize: Patients receiving oral contraceptives should be warned about the possibility of reduced efficacy if oral antibiotics are taken. It would be prudent to add other contraception during antibiotic therapy and for at least one cycle after the antibiotic is discontinued.
• Monitor: Menstrual irregularities (spotting, breakthrough bleeding) may be a sign of inadequate contraceptive hormone levels, but absence of menstrual problems does not guarantee adequate contraception.