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NBME 23 Answers

nbme23/Block 1/Question#46

A 31-year-old primigravid woman at 28 weeks' ...


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submitted by sajaqua1(212),

Tetracyclines are calcium chelating agents. Because of this, in a developing fetus or child they will bind to calcium deposits, namely teeth and bones. This can cause blue-black discoloration of teeth, and is contraindicated in pregnant mothers for this reason or in children under 8 years of age. Additionally, this same chemical property of binding to calcium is why certain divalent cations (Calcium, magnesium, iron [Fe2+]) prevent absorption of tetrayclines, and so medicines with these ions (antacids, iron supplementation) should be timed not to interfere with absorption.