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Chlorthalidone

Q: What are the absolute contraindications to chlorthalidone?

Contraindications to chlorthalidone include: Hyponatremia.Chronic kidney disease due to obstructive uropathy.Sulfonamide allergy. Use with caution in hyperkalemia, hypokalemia, hypercalcemia, hyperuricemia, and gout. Regarding use at eGFR < 30 mL/min/1.73 m², sources note it may be recommended as monotherapy or combined with a loop diuretic.

Q: How do thiazide-like diuretics differ structurally from classic thiazides?

Classic thiazides are derivatives of benzothiadiazepine. Thiazide-like diuretics belong to various chemical classes but share a similar pharmacological effect. While their heterocyclic ring structures differ, they are grouped together pharmacologically.

Q: How does chlorthalidone affect plasma uric acid levels?

Chlorthalidone increases plasma uric acid levels in a dose-dependent manner. Patients may experience a transient rise in uric acid concentration that does not require discontinuation of the drug. However, due to the risk of hyperuricemia, the diuretic should be used with caution in patients with gout, alongside regular monitoring of uric acid levels.

Q: In which nephron segment do thiazide-like diuretics act?

In the early distal convoluted tubule by blocking the Na+-Cl--cotransporter.

Q: What is the primary pharmacokinetic feature of chlorthalidone?

The drug features the longest duration of action among diuretics in this group—up to 72 hours.

Q: How does chlorthalidone affect calcium ion excretion?

Unlike sodium and potassium, urinary calcium excretion is decreased, promoting calcium retention in the body.

Chlortalidonum

For medical students2 min readUpdated 2026-10-10

Chlorthalidone (Chlortalidonum) is a thiazide-like diuretic, a long-acting agent among loop and distal diuretics. The drug is widely used in clinical practice due to its pronounced diuretic and antihypertensive effects.

FormulationTablets, 0.05 g

Pharmacological classDiuretics (thiazide-like)

Duration of effectUp to 72 hours

Renal targetEarly distal convoluted tubule (NCC)

Mechanism of Action

Chlorthalidone belongs to the thiazide-like diuretics and exerts its pharmacological effect in the early distal convoluted tubule of the nephron.

The primary target is the blockade of the $Na^+-Cl^-$-cotransporter (NCC system) on the apical (luminal) membrane of epithelial cells. Inhibition of this transport system disrupts the reabsorption of sodium and chloride ions from the tubular fluid into the interstitium, resulting in obligatory water retention in the tubular lumen and enhanced water excretion.

Pharmacological Effects and Ionogram

Blockade of salt transport alters the composition of urine:

$Na^+$ and $Cl^-$: Urinary excretion of these ions is significantly increased (primary effect).
$K^+$: Potassium excretion also increases (a secondary process driven by increased sodium delivery to the collecting ducts).
$Ca^{2+}$: Calcium ion excretion is decreased, leading to calcium retention in the body (this effect is mediated by the activation of TRPV5 calcium channels on the luminal membrane).

Therapeutic efficacy is maintained in both systemic acidosis and alkalosis. The drug is characterized by good gastrointestinal absorption upon oral administration.

Pharmacokinetics and Dosing Regimen

The main distinguishing feature of chlorthalidone among similar diuretics is its prolonged duration of action, which persists for up to 72 hours.

Formulation: Tablets, 0.05 g.
Administration: Orally at a dose of 0.025–0.1 g once daily in the morning before meals.

Due to its prolonged action, thiazide-like diuretics with this pharmacokinetic profile may occasionally be scheduled at intervals of several days, though standard outpatient regimens dictate a daily morning dose.

Place in Diuretic Classification

In the pharmacological classification of drugs affecting the renal tubular epithelium, chlorthalidone, along with indapamide and klopamide, belongs to the subgroup of thiazide-like diuretics.

Despite variations in the chemical structure of their heterocyclic rings (which visually differentiates them from classic thiazides such as hydrochlorothiazide), these compounds share a common mechanism of action on the distal convoluted tubules.

Mnemonic

Chlorthalidone is 'Chloro-Long-Done': removes chlorine and sodium, and acts long (up to 72 hours).

Frequently asked questions

What are the main clinical indications for chlorthalidone?

The primary clinical indications for chlorthalidone are arterial hypertension and certain hormone-dependent conditions.

Arterial hypertension — thiazide-like diuretics are first-line agents for uncomplicated essential hypertension, and thiazide/thiazide-like diuretics are recommended for resistant hypertension when eGFR ≥ 30 mL/min/1.73 m².
Prostate cancer — used to suppress endogenous androgen production.
Breast cancer — used in postmenopausal women (> 5 years post-menopause).

What metabolic adverse effects does chlorthalidone cause?

Chlorthalidone causes several fluid-electrolyte and carbohydrate metabolism disturbances. Key metabolic adverse effects include:

Hypokalemia — decreased serum potassium levels.
Hyponatremia — excessive sodium loss.
Hypercalcemia — calcium retention due to decreased renal excretion.
Metabolic alkalosis — acid-base balance disturbance.
Hyperuricemia — dose-dependent increase in uric acid concentration.
Insulin resistance — increased risk of developing diabetes mellitus.

What are the absolute contraindications to chlorthalidone?

Contraindications to chlorthalidone include:

Hyponatremia.
Chronic kidney disease due to obstructive uropathy.
Sulfonamide allergy.

Use with caution in hyperkalemia, hypokalemia, hypercalcemia, hyperuricemia, and gout. Regarding use at eGFR < 30 mL/min/1.73 m², sources note it may be recommended as monotherapy or combined with a loop diuretic.

How do thiazide-like diuretics differ structurally from classic thiazides?

Classic thiazides are derivatives of benzothiadiazepine. Thiazide-like diuretics belong to various chemical classes but share a similar pharmacological effect. While their heterocyclic ring structures differ, they are grouped together pharmacologically.

How does chlorthalidone affect plasma uric acid levels?