Antacids Coumarins

Inhibition of enteral coumarin absorption by adsorbents, e.g., antacids, medicinal charcoal Inhibition of hepatic coumarin metabolism, e.g., by cimetidine, metronidazole ... 

The complex formation of a coumarin derivative with magnesium ions present in antacid formulations has also been reported (Ambre and Fuher 1973). The formation of a more absorbable species of the coumarin derivative was found, i.e., magnesium-bis-hydroxy-coumarin (Dakas and Takla 1991). Complex formation is therefore not just negative for drug... 

A reduction in efficacy due to an interaction can sometimes be just as harmful as an increase patients taking warfarin who are given rifampicin need more warfarin to maintain adequate and protective anticoagulation (see Coumarins + Antibacterials Rifamycins , p.375), while patients taking tetracyclines , (p.347) or quinolones , (p.332) need to avoid antacids and milky foods (or separate their ingestion) because the effects of these antibacterials can be reduced or even abolished if admixture occurs in the gut. 

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