Interactions with oral contraceptives

Article Abstract:

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.)

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Influence of oral contraceptives on drug therapy

Article Abstract:

Oral contraceptives are among the most widely used drugs, and therefore the potential for interaction with other drugs is great. Such interaction is most likely to occur by effects among drugs on their blood levels over time, due to alterations in pharmacokinetics (absorption, distribution, metabolism, or excretion), or to effects on pharmacodynamics, at the local sites of drug action. Some of the common effects of contraceptive steroids include inhibition of liver metabolizing systems, influences on levels of proteins, including transport proteins and enzymes, and effects resulting from steroids acting through their receptors (proteins on the surface of target cells which are selective for each type of steroid). An important aspect of oral contraceptives is the large variability between individuals and in an individual over time with respect to steroid activity and handling. These issues are reviewed with respect to specific drugs. Particularly important are interactions between contraceptive steroids and antidepressants, antihypertensives, insulin, synthetic glucocorticoids such as prednisolone, theophylline, and caffeine. Patients taking oral contraceptives and one or more of these classes of drugs should be carefully monitored to ensure that the full intended therapeutic effect is achieved. (Consumer Summary produced by Reliance Medical Information, Inc.)

Dosage and administration

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Sex hormone-binding globulin-a surrogate marker for the prothrombotic effects of combined oral contraceptives

Article Abstract:

A study is conducted on thirty-five women to investigate the plausibility sex hormone - binding globulin (SHBG) concentration as a risk for venous thromboelism (VET) while using combined oral contraceptive (COC). The usefulness of SHBG as a risk marker for VTE during COC treatment is indicated by the correlation between SHBG and the risk factor activated protein C (APCr).

Sweden, Science & research, Hormones, Sex, Sex hormones, Levonorgestrel, Globulin, Globulins, Desogestrel

Similar abstracts:

• Abstracts: Oral contraception in disease states. Modern oral contraceptives and cardiovascular disease
• Abstracts: Pharmacokinetics of the contraceptive steroids levonorgestrel and gestodene after single and multiple oral administration to women

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