CHLORTHALIDONE
(klor-thal' i-done)
Hygroton, Hylidone, Novothalidone

, Thalitone, Uridon

Classifications: electrolyte & water balance agent; thiazide diuretic
Prototype: Hydrochlorothiazide
Pregnancy Category: B

Availability

15 mg, 25 mg, 50 mg, 100 mg tablets

Actions

Sulfonamide derivative. Differs chemically from thiazides but shares similar actions. Increases excretion of sodium and chloride by inhibiting their reabsorption in the cortical diluting segment of the ascending loop of Henle. Reportedly, in some patients, it causes elevations in total cholesterol, LDL cholesterol, and triglycerides.

Therapeutic Effects

Antihypertensive effect is correlated to the decrease in extracellular and intracellular volumes. Decreased volume results in reduced cardiac output with subsequent decrease in peripheral resistance.

Uses

Edema associated with CHF, renal decompensation, hepatic cirrhosis, corticosteroid and estrogen therapy; as sole agent or with other antihypertensives to treat hypertension.

Contraindications

Hypersensitivity to sulfonamide derivatives; anuria, hypokalemia; pregnancy (category B), lactation.

Cautious Use

History of renal and hepatic disease, gout, SLE, diabetes mellitus.

Route & Dosage

Hypertension
Adult: PO 12.5–25 mg/d, may be increased to 100 mg/d if needed
Child: PO 2 mg/kg 3 times/wk

Edema
Adult: PO 50–100 mg/d, may be increased to 200 mg/d if needed

Administration

Oral

Administer as single dose in a.m. to reduce potential for interrupted sleep because of diuresis.
Consult physician when chlorthalidone is used as a diuretic; an intermittent dose schedule may reduce incidence of adverse reactions.
Store tablets in tightly closed container at 15°–30° C (59°–86° F) unless otherwise advised.

Adverse Effects (1%)

CV: Orthostatic hypotension. GI: Anorexia, nausea, vomiting, diarrhea, constipation, cramping, jaundice. Hematologic: Agranulocytosis, thrombocytopenia, aplastic anemia. CNS: Dizziness, vertigo, paresthesias, headache. Metabolic: Hypokalemia, hyponatremia, hypochloremia, hypercalcemia, glycosuria, hyperglycemia, exacerbation of gout. Skin: Rash, urticaria, photosensitivity, vasculitis. Urogenital: Impotence.

Interactions

Drug: Increased risk of digoxin toxicity because of hypokalemia; corticosteroids, amphotericin B increases hypokalemia; decreases lithium elimination; may antagonize the hypoglycemic effects of sulfonylureas; nsaids may attenuate diuretic effects; cholestyramine decreases thiazide absorption.

Pharmacokinetics

Absorption: Readily absorbed from GI tract. Onset: 2 h. Peak: 3–6 h. Duration: 24–72 h. Distribution: Crosses placenta; appears in breast milk. Elimination: 30–60% excreted in urine in 24 h. Half-Life: 54 h.

Nursing Implications

Assessment & Drug Effects

Establish baseline BP measurements and check at regular intervals during period of dosage adjustment when chlorthalidone is used for hypertension.
Be alert to signs of hypokalemia (see Appendix F). Older adult patients are more sensitive to adverse effects of drug-induced diuresis because of age-related changes in the cardiovascular and renal systems.
Lab tests: Baseline and periodic: serum electrolytes (particularly K, Mg, Ca), serum uric acid, creatinine, BUN, and uric acid and blood glucose (especially in patients with diabetes).
Monitor lithium and digoxin levels closely when either of these drugs is used concurrently.

Patient & Family Education

Maintain adequate potassium intake, monitor weight, and make a daily estimate of I&O ratio.
Do not breast feed while taking this drug.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug