Drug information of Chlorthalidone


A benzenesulfonamide-phthalimidine that tautomerizes to a benzophenones form. It is considered a thiazide-like diuretic.

Mechanism of effect

Chlorthalidone inhibits sodium ion transport across the renal tubular epithelium in the cortical diluting segment of the ascending limb of the loop of Henle.

By increasing the delivery of sodium to the distal renal tubule, Chlorthalidone indirectly increases potassium excretion via the sodium-potassium exchange mechanism.


Chlorthalidone is used alone or with atenolol in the management of hypertension and edema.


  • Bioavailability: 65%
  • Onset: 2-6 hr
  • Duration: 24-72 hr
  • Peak plasma time: 1.5-6 hr
  • Protein bound: 75%
  • Metabolism:Metabolized in liver
  • Half-life: Normal renal function, 40-60 hr; anuria, 81 hr
  • Dialyzable: No
  • Total body clearance: 53-145 mL/min
  • Excretion: Urine (50-65%), feces

Drug indications

High Blood Pressure




12.5-25 mg/day PO; may increase to 50 mg qDay after a suitable trial; not to exceed 100 mg/day; usual dose range is 12.5–25 mg/day


50-100 mg/day PO or 100 mg PO every other day; not to exceed 200 mg/day

Heart Failure

12.5-25 mg/day PO; not to exceed 100 mg/day



12.5-25 mg/day PO or 12.5-25 mg PO every other day; dosages >25 mg/day offer only minimal advantage


25-100 mg/day PO; usual range, 12.5-25 mg/day


50-100 mg/day PO or 100 mg PO every other day; not to exceed 200 mg/day

Heart Failure

12.5-25 mg/day PO; not to exceed 100 mg/day


Hypertension (Off-label)

0.3 mg/kg/day PO initially; may be increased to 2 mg/kg/day; not to exceed 50 mg/day


Use with caution in diabetes mellitus, fluid or electrolyte imbalance, hypercholesterolemia, hypotension, systemic lupus erythematosus, liver disease, severe renal disease, advanced age, history of allergy or bronchial asthma

Use with caution in patients with hyperuricemia or gout; gout can be precipiated in patients with history of gout, familial predisposition to gout or chronic renal failure; risk can be increased with doses ≥25 mg (in hydrochlorothiazide equivalents)

Avoid concurrent use with lithium (reduction of lithium dosage by 50% may be necessary)

May aggravate digitalis toxicity

Electrolyte disturbances (eg, hypokalemia, hyponatremia, hypochloremic alkalosis) may occur; electrolyte distrubances can be minimized when used in combination with electrolyte sparing antihypertensives (eg, ACE inhibitors or angiotensin receptor blockers); correct hypokalemia before initiating therapy; use with caution

Avoid use of diuretics in the treatment of elevated blood pressure in patients with primary adrenal insufficiency; adjustment of glucocorticoid/ mineralocorticoid therapy and/or use of other antihypertensive agents should be considered to treat hypertension

Avoid use in patients with hypercalcemia; thiazide diuretics may decrease renal excretion of calcium

Prolonged use of thiazide diuretics reported to reduce calcium excretion; pathologic changes in parathyroid glands with hypercalcemia and hypophosphatemia reported with prolonged therapy

Therapy may cause exacerbation or activation of systemic lupus erythematosus

Points of recommendation

  • Avoid driving and doing other tasks or actions that call for you to be alert until you see how chlorthalidone affects you.
  • To lower the chance of feeling dizzy or passing out, rise slowly if you have been sitting or lying down. Be careful going up and down stairs.
  • Have your blood pressure checked often. Talk with your doctor.
  • Have blood work checked as you have been told by the doctor. Talk with the doctor.
  • This medicine may affect certain lab tests. Tell all of your health care providers and lab workers that you take chlorthalidone.
  • Talk with your doctor before you drink alcohol or use other drugs and natural products that slow your actions.
  • If you have high blood sugar (diabetes), you will need to watch your blood sugar closely. Tell your doctor if you get signs of high blood sugar like confusion, feeling sleepy, more thirst, more hungry, passing urine more often, flushing, fast breathing, or breath that smells like fruit.
  • If you are taking chlorthalidone and have high blood pressure, talk with your doctor before using OTC products that may raise blood pressure. These include cough or cold drugs, diet pills, stimulants, ibuprofen or like products, and some natural products or aids.
  • If you are on a low-salt or salt-free diet, talk with your doctor.
  • Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using chlorthalidone while you are pregnant.
  • Take chlorthalidone with food.
  • This medicine may cause you to pass urine more often. To keep from having sleep problems, try to take before 6 pm.
  • To gain the most benefit, do not miss doses.
  • Keep taking chlorthalidone as you have been told by your doctor or other health care provider, even if you feel well.
  • Drink lots of noncaffeine liquids unless told to drink less liquid by your doctor.
  • Take a missed dose as soon as you think about it.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.

Pregnancy level


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