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Apo-Chlorthalidone (CA), Hygroton (UK), Novo-Thalidone (CA), Thalitone, Uridon (CA)

Pharmacologic class: Thiazide-like diuretic

Therapeutic class: Diuretic, antihypertensive

Pregnancy risk category B


Unclear. Enhances excretion of sodium, chloride, and water by interfering with transport of sodium ions across renal tubular epithelium. Also may dilate arterioles.


Tablets: 15 mg, 25 mg, 50 mg, 100 mg

Indications and dosages

Edema associated with heart failure, renal dysfunction, cirrhosis, corticosteroid therapy, and estrogen therapy

Adults: 50 to 100 mg/day (30 to 60 mg Thalitone) P.O. or 100 mg every other day (60 mg Thalitone) P.O., up to 200 mg/day (120 mg Thalitone) P.O.

Management of mild to moderate hypertension

Adults: 25 mg/day (15 mg Thalitone) P.O. Based on patient response, may increase to 50 mg/day (30 to 50 mg Thalitone) P.O., then up to 100 mg/day (except Thalitone) P.O.


• Hypersensitivity to drug, other thiazides, sulfonamides, or tartrazine

• Renal decompensation


Use cautiously in:

• renal or severe hepatic disease, abnormal glucose tolerance, gout, systemic lupus erythematosus, hyperparathyroidism, bipolar disorder

• elderly patients

• pregnant or breastfeeding patients.


• Know that dosages above 25 mg/day are likely to increase potassium excretion without further increasing sodium excretion or reducing blood pressure.

Adverse reactions

CNS: dizziness, vertigo, drowsiness, lethargy, confusion, headache, insomnia, nervousness, paresthesia, asterixis, nystagmus, encephalopathy

CV: hypotension, ECG changes, chest pain, arrhythmias, thrombophlebitis

GI: nausea, vomiting, cramping, anorexia, pancreatitis

GU: polyuria, nocturia, erectile dysfunction, loss of libido

Hematologic: blood dyscrasias

Metabolic: gout attack, dehydration, hyperglycemia, hypokalemia, hypocalcemia, hypomagnesemia, hyponatremia, hypophosphatemia, hyperuricemia, hyperlipidemia,

hypochloremic alkalosis

Musculoskeletal: muscle cramps, muscle spasms

Skin: flushing, photosensitivity, hives, rash, exfoliative dermatitis, toxic epidermal necrolysis

Other: fever, weight loss, hypersensitivity reactions


Drug-drug. Allopurinol: increased risk of hypersensitivity reaction

Amphotericin B, corticosteroids, mezlocillin, piperacillin, ticarcillin: additive hypokalemia

Antihypertensives, barbiturates, nitrates, opiates: increased hypotension

Cholestyramine, colestipol: decreased chlorthalidone blood level

Digoxin: increased risk of hypokalemia

Lithium: increased risk of lithium toxicity

Nonsteroidal anti-inflammatory drugs: decreased diuretic effect

Drug-diagnostic tests. Bilirubin, calcium, creatinine, uric acid: increased levels

Glucose (in diabetic patients): increased blood and urine levels

Magnesium, potassium, protein-bound iodine, sodium, urine calcium: decreased levels

Drug-herbs. Ginkgo: decreased antihypertensive effects

Licorice, stimulant laxative herbs (aloe, cascara sagrada, senna): increased risk of potassium depletion

Drug-behaviors. Acute alcohol ingestion: additive hypotension

Sun exposure: increased risk of photosensitivity

Patient monitoring

• Closely monitor patient with renal insufficiency.

• Assess for signs and symptoms of hematologic disorders.

• Monitor CBC with white cell differential and serum uric acid and electrolyte levels.

• Assess for signs and symptoms of hypersensitivity reactions, especially dermatitis.

• Watch for fluid and electrolyte imbalances.

Patient teaching

• Instruct patient to consume a low-sodium diet containing plenty of potassium-rich foods and beverages (such as bananas, green leafy vegetables, and citrus juice).

• Caution patient to avoid driving and other hazardous activities until he knows whether drug makes him dizzy or affects concentration and alertness.

• Tell patient with diabetes to check urine or blood glucose level frequently.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


A diuretic that inhibits the reabsorption of sodium and chloride by the kidneys, used to treat hypertension.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Chlortalidone, a DIURETIC drug of medium potency that increases the output of urine over a period of 48 hours. Brand names are Hygroton, Kalspare, and with ATENOLOL, Tenoretic.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005