Drug interactions of metformin HCl is seen with phenprocoumon, hyperglycemic agents (eg, thiazides, corticosteroids), alcohol, furosemide, nifedipine and cationic drugs (amiloride, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, cimetidine and vancomycin). Acarbose and guar gum may reduce the absorption of metformin HCl.