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Tetracyclines - Interactions and Warnings

Concurrent ingestion of iron causes marked decreases in the bioavailability of a number of drugs including tetracycline, tetracycline derivatives (doxycycline, methacycline and oxytetracycline). The major mechanism of these drug interactions is the formation of iron-drug complexes (chelation or binding of iron by the involved drug).
- Br J Clin Pharmacol 1991 Mar;31(3):251-5 -- Iron supplements: a common cause of drug interactions. -- Campbell NR, Hasinoff BB.

There is enormous potential for drug interactions in patients who, today, often receive many drugs. Antibiotics are prominent amongst the groups of drugs commonly prescribed. Many interactions take place at the absorption stage. Antacids and antidiarrhoeal preparations, in particular, can delay and reduce the absorption of antibiotics such as tetracyclines and clindamycin, by combining with them in the gastrointestinal tract to form chelates or complexes.
- Drugs 1980 Jul;20(1):57-68 -- Adverse antibiotic drug interactions. -- Bint AJ, Burtt I.

Tetracyclines have a high affinity to form chelates with polyvalent metallic cations such as iron, aluminum, zinc, calcium and magnesium. Many of these tetracycline-metal complexes are either insoluble or otherwise poorly absorbable from the gastro-intestinal tract. An interval of 3 hours between the ingestion prevents the interaction.
- Drugs 1976;11(1):45-54 -- Interactions with the absorption of tetracyclines. -- Neuvonen PJ.

Please see: Antibiotics

last update: November 2008

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