Diuretics, barbiturates, phenytoin, rifampicin, corticosteroids, estrogens, estroprogestogens and pure progestogens may reduce the glycaemic control. Its hypoglycaemic action may be potentiated by salicylates, phenylbutazone, sulphonamides, beta-blockers, clofibric acid, vitamin k antagonist, allopurinol, theophylline, caffeine and monoamine oxidase inhibitors. Concomitant administration of micronazole, perhexiline or cimetidine with gliclazide may result in hypoglycaemia. Concomitant administration of gliclazide with agents that increase blood glucose levels should not be considered without careful monitoring of blood glucose levels to avoid hyperglycaemia. Acarbose and guar gum has been shown to decrease the oral bioavailability of metformin significantly.