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NBME 20 Answers

nbme20/Block 3/Question#33

A 31-year-old woman receives a prescription for ...

Formation of complexes with mineral ions

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submitted by laminin(7),

Tetracyclines have a high affinity to form chelates with polyvalent metallic cations such as Fe+++, Fe++, Al+++, Mg++ and Ca++. Many of these tetracycline-metal complexes are either insoluble or otherwise poorly absorbable from the gastro-intestinal tract. Milk and other dairy products, antacids containing polyvalent cations, as well as various iron salts ingested simultaneously with tetracycline derivatives, might interfere with their absorption by 50 to 90% or even more. source: https://www.ncbi.nlm.nih.gov/pubmed/946598