Phenprocoumon, thiazides, corticosteroids, alcohol, furosemide, nifedipine, amiloride, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, cimetidine & vancomycin. Acarbose & guar gum may reduce the absorption of metformin HCl.