Drug bioavailability digoxin

Proton pump inhibitors cause a profound and long-lasting inhibition of gastric acid secretion therefore, proton pump inhibitors may interfere with the absorption of drugs where gastric pH is an important determinant of bioavailability (eg, ketoconazole, ampicillin, iron salts, digoxin, cyanocobalamin). 

The pharmacokinetics of several drugs that are known P-gp substrates were not altered by GFJ in several clinical studies that investigated the effect of GFJ on the bioavailability of digoxin, amlodipine, and indinavir (27,75,99). Possible other unknown mechanisms and factors such as strength of the administered juices and length of consumption are relevant for the interactions of citrus with drugs (100). 

Erythromycin metabolites can inhibit cytochrome P450 enzymes and thus increase the serum concentrations of numerous drugs, including theophylline, oral anticoagulants, cyclosporine, and methylprednisolone. Erythromycin increases serum concentrations of oral digoxin by increasing its bioavailability. 

If the therapeutic range of a drug is broad then many substitutions can probably be made. This occurs, for example, with the penicillins. However, if there is a narrow therapeutic range then bioavailability must be carefully considered. Examples of this situation are the use of digoxin (cardiac stimulant) and phenytoin (anticonvulsive). 

Decreased bioavailability of digoxin, theophylline, cyclosporin, and phenprocoumon takes place when these drugs are combined with St. John s wort. 

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