Basic Information
ID DDInter314 and DDInter1160
Interaction RECOMMENDED: The effectiveness of estrogen-containing oral contraceptives may be impaired by concomitant treatment with antimicrobial agents. Most antimicrobials, with the exception of the rifamycins and possibly griseofulvin, do not induce hepatic enzymes and have not been shown to significantly increase the clearance of oral contraceptive estrogens. Some investigators believe that antimicrobials interfere with the enterohepatic recirculation of estrogens by decreasing bacterial hydrolytic enzymes in the gastrointestinal tract that are responsible for regenerating parent estrogen molecules following first-pass metabolism. It is possible that a small number of women may be more susceptible to contraceptive failure and, consequently, are more sensitive to the effects of antimicrobials on estrogen disposition in vivo, but risk factors or genetic predispositions have yet to be identified.
Management Until further data are available, women using oral contraceptives should be advised of the risk of breakthrough bleeding and unintended pregnancy during concomitant antimicrobial therapy. Alternative or additional methods of birth control should be considered during and for at least one week beyond the last dose of short-term antimicrobial therapy, and for at least the initial weeks of long-term antimicrobial therapy when risk may be the greatest.
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Br Med J 4 (1975): 467-8 [34] Szoka PR, Edgren RA "Drug interactions with oral contraceptives: compilation and analysis of an adverse experience report database." Fertil Steril 49(5 Suppl) (1988): s31-8 [35] London BM, Lookingbill DP "Frequency of pregnancy in acne patients taking oral antibiotics and oral contraceptives." Arch Dermatol 130 (1994): 392-3 [36] Weaver K, Glasier A "Interaction between broad-spectrum antibiotics and the combined oral contraceptive pill: a literature review." Contraception 59 (1999): 71-8 [37] Schubert W, Eriksson U, Edgar B, Cullberg G, Hedner T "Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17B-estradiol." Eur J Drug Metab Pharmacokinet 20 (1995): 219-24 [38] Weber A, Jager R, Borner A, et al. "Can grapefruit juice influence ethinyl estradiol bioavailability?" Contraception 53 (1996): 41-7
Alternative for Cefazolin J01D
Imipenem
Alternative for Mestranol -
Potential Metabolism Interactions
Substrate-Substrate Interaction：If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction：Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction：Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.