For patients who have been stabilized on metformin HCl, nonspecific gastrointestinal symptoms should not be attributed to therapy unless intercurrent illness or lactic acidosis have been excluded. Therefore, serum B 12 levels should be appropriately monitored or periodic parenteral B 12 supplementation considered. Decrease in glyburide AUC and C max were observed, but were highly variable. No information is available about the interaction of metformin and furosemide when co-administered chronically. T max and half-life were unaffected.
Nifedipine appears to enhance the absorption of metformin.
Metformin had minimal effects on nifedipine. Metformin had no effect on cimetidine pharmacokinetics. These drugs include thiazide and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blocking drugs, and isoniazid. When such drugs are administered to a patient receiving metformin HCl, the patient should be closely observed to maintain adequate glycemic control. Metformin is negligibly bound to plasma proteins and is, therefore, less likely to interact with highly protein-bound drugs such as salicylates, sulfonamides, chloramphenicol, and probenecid, as compared to the sulfonylureas, which are extensively bound to serum proteins.