No clinically important drug interactions have been identified.
Famotidine does not interact with the cytochrome P450 drug metabolizing enzyme system. Compounds metabolized by this system, which have been tested in man have included warfarin, theophylline, phenytoin, diazepam, propranolol, aminopyrine and antipyrine.
Indocyanide green as an index of hepatic blood flow and/or hepatic drug extraction has been tested and no significant effects have been found.
Studies in patients stabilised on phenprocoumon therapy have shown no pharmacokinetic interaction with famotidine and no effect on the pharmacokinetic or anticoagulant activity of phenprocoumon.
In addition, studies with famotidine have shown no augmentation of expected blood alcohol levels resulting from alcohol ingestion.
Iterations of gastric pH may affect the bioavailability of certain drugs, resulting in a decrease in the absorption of atazanavir. The absorption of ketoconazole and itraconazole could be reduced. Ketoconazole should be administered two hours before famotidine.
Probenecid inhibits the renal tubular secretion of famotidine and has been shown to cause a 50% increase in famotidine plasma concentrations. Therefore, concomitant use of probenecid and famotidine should be avoided.
Concomitant use of famotidine and antacids could reduce the famotidine absorption and lead to lower plasma levels of famotidine. Therefore, famotidine should be administered 1-2 hours before taking an antacid.
Concomitant use of sucralfate inhibits the absorption of famotidine. Therefore, sucralfate should not be administered within 2 hours of the famotidine dose.
Risk of loss of efficacy of calcium carbonate when co-administered as phosphate binder with famotidine in haemodialysis patients.
Co-administration of posaconazole oral-suspension with famotidine should be avoided if possible, since famotidine may reduce the absorption of posaconazole oral-suspension during concomitant use.
Co– administration of famotidine with the tyrosine kinase inhibitors (TKIs) dasatinib, erlotinib, gefitinib, pazopanib may decrease plasma concentrations of TKIs resulting in lower efficacy, therefore co-administration of famotidine with these TKIs is not recommended. For further specific recommendations please refer to the product information of individual TKI medicinal products.