<p>Chlortalidone prevents reabsorption of sodium and chloride by inhibiting the Na+/Cl&minus;&nbsp;symporter in the distal convoluted tubule. Thiazides and related compounds also decrease the glomerular filtration rate, which further reduces the drug&#39;s efficacy in patients with kidney impairment (e.g. kidney insufficiency). By increasing the delivery of sodium to the distal renal tubule, chlortalidone indirectly increases potassium excretion via the sodium-potassium exchange mechanism (i.e. apical ROMK/Na channels coupled with basolateral NKATPases). This can result in hypokalemia and hypochloremia as well as a mild metabolic alkalosis; however, the diuretic efficacy of chlortalidone is not affected by the acid-base balance of the patient being treated.<br />
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Initially, diuretics lower blood pressure by decreasing cardiac output and reducing plasma and extracellular fluid volume. Eventually, cardiac output returns to normal, and plasma and extracellular fluid volume return to slightly less than normal, but a reduction in peripheral vascular resistance is maintained, thus resulting in an overall lower blood pressure. The reduction in intravascular volume induces an elevation in plasma renin activity and aldosterone secretion, further contributing to the potassium loss associated with thiazide diuretic therapy.</p>