Increased lithium conc & toxicity. Valsartan: Increased incidence of hypotension, hyperkalemia & changes in renal function w/ ACE inhibitors, aliskiren. Increased K levels w/ K-sparing diuretics or K supplements, K-containing salt substitutes, drugs increasing K levels eg, heparin. Attenuated antihypertensive effects w/ NSAIDs including COX-2 inhibitors. Increased systemic exposure w/ rifampin, ciclosporin, ritonavir. Hydrochlorothiazide: Potentiated antihypertensive action of other antihypertensive drugs eg, guanethidine, methyldopa, β-blockers, vasodilators, Ca-channel blockers, ACE & direct renin inhibitors, ARBs. Potentiated action of skeletal muscle relaxants eg, curare derivatives. Increased hypokalemic effects w/ kaliuretic diuretics, corticosteroids, ACTH, amphotericin, penicillin G, carbenoxolone, salicylic acid derivatives, antiarrhythmics. Intensified hyponatremic effects w/ antidepressants, antipsychotics, antiepileptics. Weakened antihypertensive effects w/ NSAIDs including COX-2 inhibitors. Altered glucose tolerance of insulin, oral antidiabetics. Thiazide-induced hypokalemia or hypomagnesemia w/ digitalis glycosides. Increased hypersensitivity reactions to allopurinol. Increased adverse effects caused by amantadine. Reduced renal excretion & enhanced myelosuppressive effects of antineoplastic agents eg, cyclophosphamide, methotrexate. Increased bioavailability w/ anticholinergic agents. Decreased absorption by cholestyramine or colestipol. Potentiated rise in serum Ca w/ vit D. Increased risk of hyperuricemia w/ cyclosporine. Hypercalcemia w/ Ca salts. Enhanced hyperglycaemic effect of diazoxide. Hemolytic anemia w/ methyldopa. Potentiated orthostatic hypotension w/ alcohol, barbiturates, narcotics. Reduce response to pressor amines.