CHLORTHALIDONE

CHLORTHALIDONE
(klor-thal'i-done)
Thalitone
Classifications: electrolyte & water balance agent; diuretic; antihypertensive;
Therapeutic: diuretic
; antihypertensive
Prototype: Hydrochlorothiazide
Pregnancy Category: B first and second trimester; D third trimester

Availability

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

Action

Sulfonamide derivative that 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.

Therapeutic Effect

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 or thiazide derivatives; anuria, hypokalemia; pregnancy (category B in first and second trimester, and category D in third trimester), neonates with jaundice.

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 from GI tract. Onset: 2 h. Peak: 3–6 h. Duration: 24–72 h. Distribution: Crosses placenta; appears in breast milk. Elimination: 30–60% 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.

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

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