부산대학교 도서관

Drug interactions can occur when multiple medications taken by a patient boost or block one or more effects due to direct actions between the drugs or to alterations in the metabolism caused by one or both drugs. Drug interactions can be provoked by nutritional factors and by over-the-counter as well as prescription drugs. Interestingly, interference with the effects of oral contraceptives (OCs) is rare, occurring in less than five percent of patients. This article reviews the drug interactions that can interfere with the effects of OCs. Absorption of OCs may be affected by changes in intestinal motility, due to diarrhea or laxatives, for example, by drug competition at absorption sites, or by antibiotic effects on intestinal bacteria. Over 95 percent of contraceptive steroids are bound to transporting proteins in the blood, and minor changes in the extent of binding have the potential to affect OC availability. However, this appears to be relatively infrequent. Liver metabolism appears to be the major site affecting OC effectiveness, with some anticonvulsant (antiseizure) medications, antibiotics, and antibacterial drugs significantly increasing the rate of metabolism of OC steroids. High-protein diets also appear to stimulate this system, but the effects of diets low in protein and fat and of vegetarian diets are still unclear and require further study. Smoking also has the potential to increase liver metabolism of OCs, but further research is needed there, as well. The components of the OC itself also can alter subsequent availability of the steroids, with the estrogen component affecting levels of the steroid-transporting protein. As so few women apparently actually show evidence of drug interference with OC effects, further information is needed on the effects of long-term use of OCs. (Consumer Summary produced by Reliance Medical Information, Inc.)