About dexamethasonea potent synthetic glucocorticoid, antiasthmatic, anti-inflammatory and immunosuppressant.interactions for dexamethasoneendocrine system: barbiturates: decreases efficacy of dexamethasone. carbamazepine, primidone: decreases efficacy. oral contraceptives: increases efficacy of dexamethasone. ephedrine: decrease efficacy of dexamethasone. oestrogens: decrease efficacy of dexamethasone hydantoins: decrease efficacy of dexamethasone ketoconazole: increase efficacy of dexamethasone rifampicin: decreases efficacy. dexamethasone effects the actions of the following: anticholinesterases: efficacy antagonised in myasthenia gravis. oral anticoagulants: altered response. cyclosporine: increased cyclosporine efficacy leading to enhanced toxicity. digitalis glycosides: increased toxicity associated with hypokalaemia. isoniazid: decreased serum levels of isoniazid. salicylates: decreased serum levels of salicylates. diuretics: increase efficacy