Hydrochlorothiazide is not effective in patients with CrCl <30 mL/min and thus, should not be given to patients with severe renal impairment or anuria. It is also contraindicated in patients with Addison's disease. Thiazide can reduce urinary excretion of calcium, sometimes resulting in mild hypercalcemia and is therefore contraindicated to patients with preexisting hypercalcemia.