Drug interactions with contraceptive methods
Simon, P.; Hakkou, F.; Warot, D.
Contraception Fertilite Sexualite 12(3): 479-482
1984
ISSN/ISBN: 0301-861X PMID: 12265944 Document Number: 223739
3 possible types of drug interactions with contraceptives involve oral contraceptives (OCs), IUDs, and spermicides. The interaction of combined OCs with various drugs is frequently discussed in the literature, but the reported facts are sometimes contradictory. Case studies have indicated failure of OCs in patients taking ampicillin, but comparative studies using ampicillin and placebos have shown no difference in rates of estrogen, progestogens, follicle stimulating hormone, or luteinizing hormone in the 2 groups. Individual differences and predispositions among some women appear to play a role in drug interactions. The clinician should be wary of modifying accepted prescription practices too readily in the face of findings that may be explained by other as yet undisclosed factors. Interactions are difficult to establish, as are their mechanisms. They may perhaps be explained by the estrogen or progestogen components of the pills, the timing of the antibiotic dose, the duration of treatment and the dosage used, resistance of the intestinal flora, self-medication, or other factors. The drug troleandomycin is a special case; it appears to favor the already existing tendency of OCs to provoke cholestatic jaundice. A table of drug interactions with OCs can be divided into 2 parts, those that have been confirmed and whose mechanisms of action are known, including antiepileptics such as phenobarbital, butobarbital, phenytoin, and primidone, and the drug rifampicin, which are enzyme inductors; and those that are suspected but as yet unconfirmed and whose mechanism of action is not established. The unconfirmed interactions involve a variety of effects in addition to pregnancy. It is not yet established whether enzyme inductors are a greater problem for users of low-dose pills, but the probable existence of individual variations in sensitivity causes problems in setting recommendations applicable to all patients. Interactions between progestogen-only OCs and other drugs have not been reported, perhaps because they have been in use for a short time and their use is somewhat restricted. It is possible that use of anti-inflammatory drugs in midcycle attenuates the inflammatory effect of the IUD at the endometrial level, thereby augmenting the risk of pregnancy, but thus far the effect has not been proven. Drug interactions with spermicides are difficult to detect because of their less than total effectiveness, but users are warned to employ another method if they are undergoing any kind of vaginal treatment with another product.