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. Pharmacokinetics
Chlortalidone is slowly absorbed from the gastrointestinal tract after oral ingestion. It has a long half-life and therefore a prolonged diuretic action, which results in continued diuretic effects despite a skipped dose. This prolonged action of chlortalidone despite missing doses may account for the higher efficacy of chlortalidone compared to the shorter half-life medication, hydrochlorothiazide. Chlortalidone is eliminated from the body mostly by the kidney, as unchanged drug. Thus, in persons with diminished kidney function, the clearance of chlortalidone is reduced and the elimination half-life is increased.As with other thiazide diuretics, chlortalidone crosses the placenta and is excreted in breast milk. Chlortalidone may suppress lactation, and has been used for this indication. Due to its long half-life, chlortalidone may accumulate in newborns via breast milk, despite receiving only about 6% of the maternal weight-adjusted dose. Chemistry
Chlortalidone is in the sulfamoylbenzamide class. As it lacks the benzothiadiazine structure of the thiazide-type diuretics, it is called a thiazide-like diuretic.
Hyperuricemia, high levels of uric acid in the blood
Hyperglycemia, high blood sugar is more common in persons who are magnesium deficient
Hyperlipidemia, high cholesterol and triglycerides
Headache
Nausea/vomiting
Photosensitivity increased susceptibility to sunburn of skin with sun exposure
Photoonycholysis detachment of nails from nailbed with sun exposure
Weight gain
Gout; approximately doubles the risk
PancreatitisThe frequency and severity of these adverse effects is much reduced when chlortalidone is used at lower doses (e.g., 12.5 mg per day). Mechanism of action
Chlortalidone reduces reabsorption of sodium and chloride primarily through inhibition of the Na+/Cl− symporter in the apical membrane of distal convoluted tubule cells in the kidney. Although chlortalidone is often referred to as a "thiazide-like" diuretic, it is unlike thiazide diuretics in that, in addition to its inhibition of the  Na+/Cl− symporter, it also strongly inhibits multiple isoforms of carbonic anhydrase. Some of chlortalidones diuretic effect is also due to this inhibition of carbonic anhydrase in the proximal tubule. Chronic exposure to chlortalidone decreases the glomerular filtration rate. Chlortalidones diuretic effect is diminished in persons with kidney impairment. 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 Na+/K ATPases). This can result in a low blood concentration of potassium and chloride as well as a mild metabolic alkalosis; however, the diuretic effect of chlortalidone is not affected by the acid-base balance of the person being treated. There is uncertainty about the mechanism of the blood pressure-lowering effect that occurs during chronic exposure to chlortalidone.