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Chlorothiazide (Monograph)

Brand name: Diuril
Drug class: Thiazide Diuretics
- Diuretics, Thiazide
VA class: CV701
CAS number: 58-94-6

Medically reviewed by on Mar 15, 2023. Written by ASHP.


Thiazide diuretic and antihypertensive agent.

Uses for Chlorothiazide


Used alone or in combination with other antihypertensive agents for all stages of hypertension.

Thiazide diuretics are recommended as one of several preferred agents for the initial management of hypertension according to current evidence-based guidelines; other preferred options include ACE inhibitors, angiotensin II receptor antagonists, and calcium-channel blockers. While there may be individual differences with respect to recommendations for initial drug selection and use in specific patient populations, current evidence indicates that these antihypertensive drug classes all generally produce comparable effects on overall mortality and cardiovascular, cerebrovascular, and renal outcomes.

Individualize choice of therapy; consider patient characteristics (e.g., age, ethnicity/race, comorbidities, cardiovascular risk) as well as drug-related factors (e.g., ease of administration, availability, adverse effects, cost).

A 2017 ACC/AHA multidisciplinary hypertension guideline classifies BP in adults into 4 categories: normal, elevated, stage 1 hypertension, and stage 2 hypertension. (See Table 1.)

Source: Whelton PK, Carey RM, Aronow WS et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Hypertension. 2018;71:e13-115.

Individuals with SBP and DBP in 2 different categories (e.g., elevated SBP and normal DBP) should be designated as being in the higher BP category (i.e., elevated BP).

Table 1. ACC/AHA BP Classification in Adults1200


SBP (mm Hg)

DBP (mm Hg)









Hypertension, Stage 1




Hypertension, Stage 2




The goal of hypertension management and prevention is to achieve and maintain optimal control of BP. However, the BP thresholds used to define hypertension, the optimum BP threshold at which to initiate antihypertensive drug therapy, and the ideal target BP values remain controversial.

The 2017 ACC/AHA hypertension guideline generally recommends a target BP goal (i.e., BPs to achieve with drug therapy and/or nonpharmacologic intervention) of <130/80 mm Hg in all adults regardless of comorbidities or level of atherosclerotic cardiovascular disease (ASCVD) risk. In addition, an SBP goal of <130 mm Hg generally is recommended for noninstitutionalized ambulatory patients ≥65 years of age with an average SBP of ≥130 mm Hg. These BP goals are based upon clinical studies demonstrating continuing reduction of cardiovascular risk at progressively lower levels of SBP.

Other hypertension guidelines generally have based target BP goals on age and comorbidities. Guidelines such as those issued by the JNC 8 expert panel generally have targeted a BP goal of <140/90 mm Hg regardless of cardiovascular risk and have used higher BP thresholds and target BPs in elderly patients compared with those recommended by the 2017 ACC/AHA hypertension guideline.

Some clinicians continue to support previous target BPs recommended by JNC 8 due to concerns about the lack of generalizability of data from some clinical trials (e.g., SPRINT study) used to support the 2017 ACC/AHA hypertension guideline and potential harms (e.g., adverse drug effects, costs of therapy) versus benefits of BP lowering in patients at lower risk of cardiovascular disease.

Consider potential benefits of hypertension management and drug cost, adverse effects, and risks associated with the use of multiple antihypertensive drugs when deciding a patient's BP treatment goal.

For decisions regarding when to initiate drug therapy (BP threshold), the 2017 ACC/AHA hypertension guideline incorporates underlying cardiovascular risk factors. ASCVD risk assessment recommended by ACC/AHA for all adults with hypertension.

ACC/AHA currently recommend initiation of antihypertensive drug therapy in addition to lifestyle/behavioral modifications at an SBP ≥140 mm Hg or DBP ≥90 mm Hg in adults who have no history of cardiovascular disease (i.e., primary prevention) and a low ASCVD risk (10-year risk <10%).

For secondary prevention in adults with known cardiovascular disease or for primary prevention in those at higher risk for ASCVD (10-year risk ≥10%), ACC/AHA recommend initiation of antihypertensive drug therapy at an average SBP ≥130 mm Hg or an average DBP ≥80 mm Hg.

Adults with hypertension and diabetes mellitus, chronic kidney disease (CKD), or age ≥65 years are assumed to be at high risk for cardiovascular disease; ACC/AHA state that such patients should have antihypertensive drug therapy initiated at a BP ≥130/80 mm Hg. Individualize drug therapy in patients with hypertension and underlying cardiovascular or other risk factors.

In stage 1 hypertension, experts state that it is reasonable to initiate drug therapy using the stepped-care approach in which one drug is initiated and titrated and other drugs are added sequentially to achieve the target BP. Initiation of antihypertensive therapy with 2 first-line agents from different pharmacologic classes recommended in adults with stage 2 hypertension and average BP >20/10 mm Hg above BP goal.

Black hypertensive patients generally tend to respond better to monotherapy with thiazide diuretics or calcium-channel blockers than to other antihypertensive drug classes (e.g., ACE inhibitors, angiotensin II receptor antagonists). However, the combination of an ACE inhibitor or an angiotensin II receptor antagonist with a calcium channel blocker or thiazide diuretic produces similar BP lowering in black patients as in other racial groups.

Thiazides may be preferred in hypertensive patients with osteoporosis. Secondary beneficial effect in hypertensive geriatric patients of reducing the risk of osteoporosis due to effect on calcium homeostasis and bone mineralization.

Edema (General)

Management of edema resulting from various causes; diagnose etiology before use.

Edema caused by renal disease or by corticosteroids or estrogens may be relatively resistant to treatment.

Ineffective in patients with Scr or BUN concentrations greater than twice normal.

May be ineffective in patients with GFR <15–25 mL/minute; even when GFR is 25–50 mL/minute, more potent (e.g., loop) diuretics may be indicated.

No substantial difference in clinical effects or toxicity of comparable thiazide or thiazide-like diuretics except metolazone may be more effective in edema with renal impairment.

Edema in Heart Failure

Management of edema associated with heart failure.

Most experts state that all patients with symptomatic heart failure who have evidence for, or history of, fluid retention generally should receive diuretic therapy in conjunction with moderate sodium restriction, an agent to inhibit the renin-angiotensin-aldosterone (RAA) system (e.g., ACE inhibitor, angiotensin II receptor antagonist, angiotensin receptor-neprilysin inhibitor [ARNI]), a β-adrenergic blocking agent (β-blocker), and in selected patients, an aldosterone antagonist.

Loop diuretics (e.g., bumetanide, ethacrynic acid, furosemide, torsemide) are diuretics of choice for most patients with heart failure.

Do not use diuretics as monotherapy in heart failure even if symptoms (e.g., peripheral edema, pulmonary congestion) are well controlled; diuretics alone do not prevent progression of heart failure.

Diuretics produce rapid symptomatic benefits, relieving pulmonary and peripheral edema more rapidly (within hours or days) than cardiac glycosides, ACE inhibitors, or β-blockers (in weeks or months).

Diuretics should be continued in heart failure and comorbid conditions (e.g., hypertension) where ongoing therapy with the drugs are indicated.

Edema Secondary to Nephrotic Syndrome

May be useful if the patient fails to respond to corticosteroid therapy.

More likely to become refractory to thiazides than edema associated with congestive heart failure, and more potent diuretics may be required.

Edema in Pregnancy

Generally responds well to thiazides except when caused by renal disease.

Thiazides should not be used for routine therapy in pregnant women with mild edema who are otherwise healthy.

Chlorothiazide Dosage and Administration


Monitoring and BP Treatment Goals


Administer orally or IV. Manufacturer states that IV preparations not indicated for hypertension management.

The injection must not be administered subcutaneously or IM, and extravasation of the alkaline solution must be avoided.

Oral Administration

Administer chlorothiazide tablets and suspension orally.

IV Administration

For solution and drug compatibility information, see Compatibility under Stability.

Administer chlorothiazide sodium by slow IV injection or by IV infusion; use IV route only when patients unable to take drug orally or in emergency situations.

Must avoid extravasation of the alkaline solution.


Reconstitute only with sterile water for injection.

Add 18 mL of sterile water for injection to 500-mg vial; provides a solution containing about 28 (27.8) mg/mL. Use no less than 18 mL of diluent for initial reconstitution.


May administer injection undiluted or may further dilute with sodium chloride, dextrose, or other compatible infusion fluids before administration.

Rate of Administration

Slowly by direct IV injection or by IV infusion.


Dosage of chlorothiazide sodium is expressed in terms of chlorothiazide.

IV and oral dosage are identical.

Individualize dosage according to requirements and response.

If added to potent hypotensive agent regimen, initially reduce dosage of hypotensive agent to avoid possibility of severe hypotension.

For the management of fluid retention associated with heart failure, experts state that diuretics should be administered at a dosage sufficient to achieve optimal volume status and relieve congestion without inducing excessively rapid reduction in intravascular volume, which could result in hypotension, renal dysfunction, or both.

Pediatric Patients


Infants <6 months of age: May require up to 30 mg/kg daily given in 2 divided doses.

Children 6 months to 12 years of age: Usually 10–20 mg/kg daily in 1 or 2 divided doses.

Experts recommend initiation of drug at low end of dosage range; may increase dosage every 2–4 weeks until BP controlled, maximum dosage reached, or adverse effects occur.


Infants <6 months of age: May require up to 30 mg/kg daily given in 2 divided doses.

Children 6 months to 12 years of age: Usually 10–20 mg/kg daily in 1 or 2 divided doses.


Experience in infants and children is limited, and IV use in this age group generally is not recommended.



Initially, 0.5–1 g daily as a single dose or in 2 divided doses.

Adults rarely may require up to 2 g daily in divided doses.

If adequate response is not achieved with monotherapy, add another antihypertensive agent.


Usually, 0.5–1 g daily in 1 or 2 doses. Occasionally, up to 2 g daily in 1 or 2 doses.

After several days or when nonedematous weight is attained, dosage reduction to a lower maintenance level may be possible.

Management of fluid retention associated with heart failure: Some experts recommend initiating chlorothiazide at a low dosage (e.g., 250–500 mg once or twice daily) and increasing dosage until urine output increases and weight decreases, generally by 0.5–1 kg daily.

With an intermittent dosing schedule, excessive response and the resulting undesirable electrolyte imbalance are less likely to occur.


Usually, 0.5–1 g daily in 1 or 2 doses. Occasionally, up to 2 g daily in 1 or 2 doses.

After several days or when nonedematous weight is attained, dosage reduction to a lower maintenance level may be possible.

With an intermittent schedule, excessive response and the resulting undesirable electrolyte imbalance are less likely to occur.

For sequential nephron blockade in the management of fluid retention in heart failure, some experts recommend an initial dosage of 0.5–1 g once daily in combination with a loop diuretic.

Prescribing Limits

Pediatric Patients


Infants <2 years of age: Maximum of 375 mg daily.

Children ≥2 years of age: 1 g daily.



Rarely, up to 2 g daily in divided doses may be required.


Maximum recommended by manufacturer: 2 g daily in divided doses.

Management of fluid retention in heart failure: 1 g maximum daily dosage recommended by ACCF/AHA.


Maximum of 2 g daily in divided doses.

Special Populations

Hepatic Impairment

No specific dosage recommendations for hepatic impairment; caution because of risk of precipitating hepatic coma.

Renal Impairment

No specific dosage recommendations for renal impairment; caution because of risk of precipitating azotemia.

Geriatric Patients

No specific geriatric dosage recommendations.

Cautions for Chlorothiazide




Hypotensive Agents

May potentiate effects of other hypotensive agents. Although additive or potentiated antihypertensive effect usually is used to therapeutic advantage, hypotension could occur. (See Interactions.)

Lupus Erythematosus

Possible exacerbation or activation of systemic lupus erythematosus.


Generally, do not use with lithium salts. (See Interactions.)

Sensitivity Reactions


May occur with or without history of allergy or bronchial asthma.

Sulfonamide cross-sensitivity unlikely. (See Contraindications under Cautions.)

General Precautions

Electrolyte Imbalance

Monitor for fluid or electrolyte imbalance (hyponatremia, hypochloremic alkalosis, hypokalemia).

Observe for signs of electrolyte imbalance (e.g., dryness of mouth, thirst, weakness, lethargy, drowsiness, restlessness, confusion, seizures, oliguria, muscle pains, cramps, muscular fatigue, hypotension, tachycardia, nausea, vomiting).

Perform periodic serum electrolyte determinations (particularly of potassium, sodium, chloride, and bicarbonate); institute measures to maintain normal serum electrolyte concentrations if necessary.

Serum and urinary electrolyte measurements are especially important with diabetes mellitus, vomiting, diarrhea, parenteral fluid therapy, or expectations of excessive diuresis.

Weekly (or more frequent) electrolyte measurement early in treatment; possible to extend interval between measurements to ≥3 months when electrolyte response has stabilized.


May occur after brisk diuresis, when cirrhosis is present, or with prolonged therapy; inadequate oral electrolyte intake may contribute.

May cause cardiac arrhythmias, exaggerate cardiac response to cardiac glycoside toxicity (increase ventricular irritability).

Use potassium-sparing diuretics and/or potassium supplementation to avoid or treat hypokalemia.


Generally mild, usually does not require specific treatment except in renal or hepatic impairment.

Chloride replacement may be required for metabolic acidosis.


Dilutional hyponatremia may occur in edematous patients in hot weather; appropriate treatment usually is water restriction rather than salt administration except when hyponatremia is life-threatening.

In actual salt depletion, appropriate replacement is treatment of choice.


Hyperuricemia or, rarely, precipitation of gout may occur; generally avoid or use with caution in patients with history of gout unless patient is receiving uric acid lowering therapy.


In diabetic patients, dosage adjustment of insulin or oral hypoglycemics may be required; hyperglycemia may occur and latent diabetes mellitus may become evident.


Antihypertensive effect may be enhanced after sympathectomy.


May increase magnesium urinary excretion, resulting in hypomagnesemia.


May decrease calcium urinary excretion, cause slight intermittent serum calcium increase in absence of known calcium metabolism disorder; marked hypercalcemia may indicate hyperparathyroidism.

Discontinue parathyroid tests.


May increase cholesterol and triglyceride concentrations.

Clinical importance of these changes is unknown. Diet low in saturated fat and cholesterol usually compensates.

Hypotensive Effects

Orthostatic hypotension occurs rarely.

Specific Populations


Category C.

Diuretics are considered second-line agents for control of chronic hypertension in pregnant women; if initiation of antihypertensive therapy is necessary in a pregnant woman, other antihypertensives (i.e., methyldopa, nifedipine, labetalol) are preferred.

Edema associated with pregnancy generally responds well to thiazides except when caused by renal disease; however, routine use not recommended in pregnant women with mild edema who are otherwise healthy.

Diuretics are not recommended for prevention or management of gestational hypertension or preeclampsia.


Distributed into milk. Manufacturer states to discontinue nursing or the drug; however, considered to be compatible with breast-feeding.

Pediatric Use

No controlled studies in children; use is supported by experience and published literature about hypertension treatment in children.

Experience with IV chlorothiazide sodium in infants and children is limited, and IV use in this age group generally is not recommended.

Geriatric Use

Elderly may be at increased risk of dilutional hyponatremia, especially underweight females with poor oral fluid and electrolyte intake or excessive low-sodium nutritional supplement intake. (See Hyponatremia under Cautions.)

Hepatic Impairment

Use with caution in patients with hepatic impairment or progressive liver disease (particularly with associated potassium deficiency); electrolyte imbalance may precipitate hepatic coma.

Discontinue immediately if signs of impending hepatic coma appear.

Renal Impairment

Use with caution in severe renal impairment; thiazides decrease GFR and may precipitate azotemia. Effects may be cumulative in impaired renal function.

Consider interruption or discontinuance if progressive renal impairment (rising nonprotein nitrogen, BUN, or Scr) occurs.

Common Adverse Effects

Potassium depletion, hyperuricemia (usually asymptomatic; rarely leading to gout). Hypochloremic alkalosis in patients at risk (e.g., hypokalemic patients). Hyperglycemia and glycosuria in diabetics.

Drug Interactions

Specific Drugs and Laboratory Tests

Drug or Test




Increased risk of postural hypotension


Thiazides may cause slightly more alkaline urinary pH; may decrease urinary excretion of some amines (e.g., amphetamine) with concurrent use

Urine pH change is not great during thiazide use and, toxic blood concentrations of amines usually do not occur

Monitor for signs of toxicity after initiation of thiazides in patients receiving amphetamine

Amphotericin B

Additive/potentiated potassium loss

Severe potassium depletion may occur when used concomitantly

Anticoagulants, oral

Postulated that may antagonize oral anticoagulant effects

Confirmatory evidence is lacking

Antidiabetic agents (sulfonylureas)

Thiazide hyperglycemic effect may exacerbate diabetes mellitus, increase antidiabetic agent requirements, and/or cause temporary loss of diabetic control or secondary failure to antidiabetic agent


Increased risk of postural hypotension with thiazides

Cholestyramine or colestipol

May bind thiazides, reduce their GI absorption, with cholestyramine reportedly producing greater binding in vitro

Administer thiazides ≥2 hours before cholestyramine or colestipol when used concomitantly


Additive/potentiated potassium loss

Severe potassium depletion may occur when used concomitantly


Additive/potentiated potassium loss

Severe potassium depletion may occur when used concomitantly


May potentiate diazoxide hyperglycemic, hypotensive, and hyperuricemic effects

Use concomitantly with caution

Digitalis glycosides

Thiazide-induced electrolyte disturbances (principally hypokalemia, but also hypomagnesemia and hypercalcemia) may increase digitalis toxicity risk

Perform periodic electrolyte determinations with concomitant use; correct hypokalemia if warranted

Hypotensive agents

Increased hypotensive effects of most other hypotensive agents

Addition of thiazide to stabilized regimen with potent hypotensive agent (e.g., guanethidine sulfate, methyldopa, ganglionic blocking agent) may cause severe postural hypotension

Usually used to therapeutic advantage


May exacerbate diabetes mellitus, increase insulin requirements, cause temporary loss of diabetic control, or secondary failure to insulin


Thiazides (sometimes used with lithium to reduce lithium-induced polyuria), Reduced renal lithium clearance within several days

Can increase serum lithium concentrations and the risk of lithium intoxication

Occasionally, used to therapeutic advantage to reduce lithium-induced polyuria, but reduce lithium dosage by about 50% and monitor serum lithium carefully

Generally, avoid concomitant use because of increased lithium toxicity risk


Urinary alkalinization may decrease the effectiveness of methenamine compounds which require a urinary pH of ≤5.5 for optimal activity

Monitor urine pH during concurrent therapy


Increased risk of NSAIA-induced renal failure secondary to prostaglandin inhibition and decreased renal blood flow

NSAIAs may interfere with the natriuretic, diuretic, and antihypertensive response to diuretics

Monitor closely for possible adverse effects and/or attenuation of diuretic-induced therapeutic effects during concomitant use

Neuromuscular blocking agents (e.g., tubocurarine chloride or gallamine triethiodide [both no longer commercially available in US])

May cause prolonged neuromuscular blockade

Confirmatory evidence lacking


Increased risk of postural hypotension with thiazides


Blocks thiazide-induced uric acid retention

Also blocks renal tubular secretion of thiazide, but effect on thiazide duration of action apparently not studied

Apparently enhances excretion of calcium, magnesium, and citrate during thiazide therapy, but urinary calcium concentrations remain below normal

Sodium, potassium, ammonia, chloride, bicarbonate, phosphate, and titratable acid excretion apparently not affected by concomitant probenecid and thiazide therapy

Used to therapeutic advantage


Thiazides may cause slightly more alkaline urinary pH; may decrease urinary excretion of some amines (e.g., quinidine) with concurrent use

Urine pH change is not great during thiazide use and toxic blood concentrations of amines usually do not occur

Monitor for signs of toxicity after initiation of thiazide

Test, amylase (serum)

Values may be increased substantially in both asymptomatic patients and in patients developing acute pancreatitis who are receiving thiazides

Test, corticosteroids (urinary) (Glenn-Nelson technique)

Decreased values by interfering in vitro with the absorbance in the modified Glenn-Nelson technique for urinary 17-hydroxycorticosteroids; may also decrease urinary cortisol excretion

Importance of effect on urinary corticosteroids is unclear

Test, estrogens (spectrophotometric assay of total urinary estrogen; assay of estradiol)

Although hydrochlorothiazide causes falsely decreased values, similar interference does not occur with chlorothiazide

Test, histamine for pheochromocytoma

False-negative results

Test, parathyroid function tests

May elevate serum calcium in the absence of known disorders of calcium metabolism

Discontinue thiazides prior to performing parathyroid function tests

Test, phenolsulfonphthalein (PSP)

Thiazides compete with PSP for secretion by the proximal renal tubules

Importance unknown

Test, phentolamine

False-negative results

Test, protein-bound iodine (PBI)

Values may be decreased, although usually not to subnormal

Test, triiodothyronine resin uptake

Decreased slightly, but 24-hour I 131 uptake is not affected

Test, tyramine

False-negative results

Vasopressors (e.g., norepinephrine)

Possible decreased arterial responsiveness to vasopressor amines

Clinical importance not established; decrease in pressor response not sufficient to preclude vasopressor use

Chlorothiazide Pharmacokinetics



Incompletely and variably absorbed from the GI tract.

Absorption from the GI tract appears to be site specific and saturable. Several studies indicate that about 50 mg is absorbed following oral administration of a single 250-mg tablet, a single 500-mg tablet, or two 250-mg tablets to fasting healthy individuals.


Diuretic effect (oral): within 2 hours; peak effect in 3–6 hours.

Diuretic effect (IV): within 15 minutes; peak effect in 30 minutes.

Hypotensive effect (oral): generally 3–4 days.


Diuretic effect: 6–12 hours.


Concomitant administration with food appears to increase the extent of absorption.



Distributed in the extracellular space.

Readily crosses the placenta.

Distributed into breast milk.



Not metabolized.

Elimination Route

Excreted unchanged in urine; about 95% of an IV dose is eliminated in 5 hours and about 20 or 10% of a 250- or 500-mg oral dose, respectively, is eliminated in 48–72 hours.


45–120 minutes.





Tight, light-resistant containers at 20–25°C.


Tight containers at 15–30°C; avoid freezing.


Powder for Injection




Solution CompatibilityHID


Dextrose–Ringer’s injection combinations

Dextrose–Ringer’s injection, lactated, combinations

Dextrose–saline combinations

Dextrose 5% in sodium chloride 0.9%

Dextrose 2.5, 5, or 10% in water

Ionosol MB with dextrose 5%

Ionosol T with dextrose 5%

Ringer’s injection

Ringer’s injection, lactated

Sodium chloride 0.45 or 0.9%

Sodium lactate (1/6) M


Ionosol B with dextrose 5%

Normosol M in dextrose 5%

Normosol R in dextrose 5%

Drug CompatibilityHID
Admixture Compatibility


Lidocaine HCl

Nafcillin sodium

Ranitidine HCl


Amikacin sulfate

Chlorpromazine HCl

Hydralazine HCl

Polymyxin B sulfate

Prochlorperazine mesylate

Promethazine HCl


Advice to Patients


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name



Dosage Forms


Brand Names




250 mg/5 mL




250 mg*

Chlorothiazide Tablets

500 mg*

Chlorothiazide Tablets

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Chlorothiazide Sodium


Dosage Forms


Brand Names



For injection, for IV use only

500 mg (of chlorothiazide)*

Sodium Diuril


AHFS DI Essentials™. © Copyright 2024, Selected Revisions March 25, 2019. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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