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All about: Chlorthalidone

Big Image Pronouncation: (klor-THAL-ih-dohn)
Class: Thiazide diuretic

Trade Names:
- Tablets 25 mg
- Tablets 50 mg
- Tablets 100 mg

Trade Names:
- Tablets 15 mg

Apo-Chlorthalidone (Canada)

Mechanism of Action


Inhibits reabsorption of sodium and chloride in proximal portion of distal convoluted tubules.



64% absorbed.


Excreted in breast milk.


The t ½ is 40 h.


2 to 3 h.


2 to 6 h.


24 to 72 h.

Indications and Usage

Reduction of edema associated with CHF, hepatic cirrhosis, renal function impairment, corticosteroid and estrogen therapy; management of hypertension.

Unlabeled Uses

Treatment of calcium nephrolithiasis, osteoporosis, diabetes insipidus.


Hypersensitivity to thiazides, related diuretics, or sulfonamide-derived drugs; anuria; renal decompensation.

Dosage and Administration


PO 50 to 200 mg daily or on alternate days.


PO 25 to 100 mg daily. Doses above 25 mg/day potentiate potassium excretion but do not benefit sodium excretion or BP reduction.

Drug Interactions


Concurrent use may increase incidence of hypersensitivity reactions to allopurinol.

Amphotericin B, corticosteroids

May intensify potassium depletion.


May increase chlorthalidone absorption.


May diminish anticoagulant effects.

Bile acid sequestrants

May reduce chlorthalidone absorption. Give chlorthalidone at least 2 h before bile acid sequestrant.

Calcium salts

Hypercalcemia may develop.


May cause hyperglycemia.

Digitalis glycosides

Diuretic-induced hypokalemia and hypomagnesemia may precipitate digitalis-induced arrhythmias.


May decrease renal excretion of lithium.

Loop diuretics

Synergistic effects may result in profound diuresis and serious electrolyte abnormalities.

Methenamines, NSAIDs

May decrease effectiveness of chlorthalidone.

Sulfonylureas, insulin

May decrease hypoglycemic effect of sulfonylureas.

Laboratory Test Interactions

Increased serum bilirubin levels. Serum magnesium levels in uremic patients may be increased.

Adverse Reactions


Dizziness; lightheadedness; vertigo; headache; paresthesias; weakness; restlessness; insomnia.


Purpura; photosensitivity; rash; urticaria; necrotizing angiitis; vasculitis; cutaneous vasculitis; exfoliative dermatitis; toxic epidermal necrolysis.


Xanthopsia (yellow vision).


Anorexia; gastric irritation; nausea; vomiting; abdominal pain or cramping; bloating; diarrhea; constipation; pancreatitis.


Impotence; reduced libido.


Leukopenia; thrombocytopenia; agranulocytosis; aplastic or hypoplastic anemia.




Hyperglycemia; glycosuria; hyperuricemia; fluid and electrolyte imbalances.


Muscle cramps or spasms.



Category B .


Excreted in breast milk.


Safety and efficacy not established.


May occur in patients with or without history of allergy or bronchial asthma; cross-sensitivity with sulfonamides also may occur.

Renal Function

May precipitate azotemia; use with caution.

Hepatic Function

Minor alterations of fluid and electrolyte balance may precipitate hepatic coma; use with caution.


May cause increased concentrations of total serum cholesterol, total triglycerides, and LDL in some patients.

Postsympathectomy patients

Antihypertensive effects may be enhanced.



Orthostatic hypotension, dizziness, drowsiness, syncope, potassium depletion, nausea, vomiting, lethargy, coma, GI irritation, GI hypermotility, seizures.

Patient Information

  • Teach patient signs and symptoms of hypokalemia (eg, weakness, cramps, nausea, dizziness), especially if patient is taking digitalis.
  • Explain diuretic effects of drug so patient is aware of expected and potential outcomes.
  • Instruct patient to follow low-sodium diet to enhance action of medication.
  • If high-potassium diet is recommended by health care provider, help patient identify appropriate meal plans or potassium supplements.
  • Teach patient to record weight daily at a consistent time and to notify health care provider if weight fluctuates 5 or more pounds.
  • Tell patient to notify health care provider of salt or water retention occurs (eg, swelling of feet, ankles, calves).
  • Caution patient to avoid exposure to sunlight and to use sunscreen or wear protective clothing to avoid photosensitivity reaction.
  • Advise patient to avoid sudden position changes to prevent orthostatic hypotension. Have patient get up slowly and dangle feet before getting out of bed.

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