The thiazides reduce urine volume primarily by reducing extracellular fluid volume and increasing water reabsorption at early portions of the nephron. The main action of thiazides is thought to be inhibition of a protein that transports sodium chloride in the distal nephron, which results in an increased loss of sodium, chloride and water in the urine. Thiazides can also cause increased potassium and magnesium loss and decreased calcium loss in the urine. Potassium supplements may be given to correct the deficiency. The ability to decrease calcium excretion has caused these drugs to be used in patients with a tendency to form calcium containing kidney stones .
Thiazide diuretics can cause elevated blood sugar in diabetics .
There may be cross-sensitivity between people with allergies to sulfa antibiotics and the thiazide diuretics. Thiazides can decrease excretion of uric acid by the kidney and may precipitate a gout attack in patients with this disease. The ability to decrease potassium levels is increased by simultaneous use of other drugs that can cause potassium loss including corticosteroids . Thiazides may increase sensitivity to the sun in certain people, therefore a sunscreen is recommended. Osmotic diuretics are generally used in a hospital setting.