Interaction between Oxytetracycline and Ethinylestradiol
Moderate
Absorption
| ID | DDInter1374 and DDInter692 |
| Interaction | RECOMMENDED: The effectiveness of estrogen-containing oral contraceptives may be impaired by concomitant treatment with antimicrobial agents. The non-hormonal placebo pills included in some oral contraceptive preparations may contain iron, usually ferrous fumarate. Concomitant administration of these iron pills may significantly decrease the gastrointestinal absorption of antibiotics such as quinolones and tetracyclines. The mechanism is chelation of the antibiotic by the iron cation, forming a complex that is poorly absorbed from the gastrointestinal tract. |
| 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. In general, quinolone antibiotics should be dosed either 2 to 4 hours before or 4 to 6 hours after iron preparations to minimize the potential for interaction. The administration of tetracycline antibiotics and iron preparations should be separated by at least three to four hours, although this may not prevent the interaction with doxycycline. Concomitant use of doxycycline and iron preparations should be avoided if possible. |
| References | |
| Alternative for Oxytetracycline |
J01A
S01A
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| Alternative for Ethinylestradiol |
G03A
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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.