Tetracyclines Iron compounds

The absorption of both the tetracyclines and iron compounds is markedly reduced by concurrent use, leading to reduced serum levels of the tetracyclines. Their therapeutic effectiveness may be reduced or even abolished. 

The interactions between the tetracyclines and iron compounds are well-documented, well-established, and of clinical importance. The 30 to 90% reductions in serum tetracycline levels that are caused by iron are so large that tetracycline levels may fall below the MIC. However, the extent of the reductions depends on a number of factors. 

An established and moderately well documented interaction of clinical importance. Separate the administration of tetracycline and zinc compounds as much as possible to minimise admixture in the gut. In the case of iron , (p.348), which interacts by the same mechanism, 2 to 3 hours is usually enough. Alternatively it would seem that doxycycline is less affected, so it may be a useful alternative. Other tetracyclines would be expected to interact like tetracycline itself, but this needs confirmation. The small reduction in serum zinc concentrations is likely to be of little practical importance. ... 

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