ATC Code C03BA04
Formula C14H11ClN2O4S
Molar Mass (g·mol−1) 338,77
Melting Point (°C) 224–226
CAS Number 77-36-1
PUB Number 2732
Drugbank ID DB00310


Chlorthalidone is an active ingredient that belongs to the class of thiazide diuretics. These are used to flush excess water out of the body. It is used either alone or in combination with other antihypertensives. The main indications of the substance include:

  • Hypertension
  • Edema
  • Heart failure
  • Supportive for recurrent urinary tract infections in women.

The active substance is taken orally in the form of a tablet. Chorlthalidone was first marketed in 1960 by Geigy (now Novartis) and is included in the WHO list of essential medicines.


Pharmacodynamics and mechanism of action

Chlorthalidone acts by binding to the Na+/Cl- symporter channel in the renal tubules, blocking the reabsorption of sodium and chloride, and the ions are excreted in the urine. The osmotic effect results in increased excretion of water as well. This increased excretion of fluid results in a decrease in blood volume and thus a decrease in blood pressure.


Chlorthalidone is absorbed via the gastrointestinal tract after peroral administration and is rapidly absorbed. It concentrates more in erythrocytes and diffuses from them only slowly back into the serum, giving it a relatively large volume of distribution. Approximately 75 percent of the drug is bound to plasma proteins, with 58 percent of the drug bound to albumin. Approximately 50 percent of the administered dose is excreted unchanged by the kidney. The other half is metabolized by the liver and also excreted by the kidneys. The half-life is approximately 40-50 hours.

Drug Interactions

There are a number of drug interactions that must be considered when taking chlorthalidone. For example, it may decrease the effectiveness of insulin and other antidiabetic drugs and slow the excretion of lithium, which may increase the risk of side effects due to its low therapeutic range. Dose adjustment should be performed in this case.

Attention should also be paid to the synergistic effect of the agent together with other antihypertensives. Joint use, if unintentional, may result in excessive blood pressure reduction and associated symptoms.


Side effects

Like all medicines, chlortalidone can cause side effects, including:

  • drowsiness
  • headache
  • dizziness
  • muscle weakness
  • nausea
  • constipation
  • Hypokalemia
  • Hyponatremia
  • Hypercalcemia
  • Hyperuricemia
  • Weight gain
  • Increased risk of gout

In rare cases, allergic reactions or the development of pancreatitis may also occur.

Contraindications and precautions

Chlorthalidone is contraindicated in patients with renal failure, dehydration, hypokalemia, and in pregnant women. It should also not be taken by patients who are hypersensitive to the active substance or other thiazide diuretics.

Markus Falkenstätter

Markus Falkenstätter

Markus Falkenstätter ist Autor zu pharmazeutischen Themen in der Medizin-Redaktion von Medikamio. Er befindet sich im letzten Semester seines Pharmaziestudiums an der Universität Wien und liebt das wissenschaftliche Arbeiten im Bereich der Naturwissenschaften.

Mag. pharm Stefanie Lehenauer

Mag. pharm Stefanie Lehenauer

Stefanie Lehenauer ist seit 2020 freie Autorin bei Medikamio und studierte Pharmazie an der Universität Wien. Sie arbeitet als Apothekerin in Wien und ihre Leidenschaft sind pflanzliche Arzneimittel und deren Wirkung.

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