Classifications: thiazide-like diuretic; antihypertensive;
Therapeutic: antihypertensive; thiazide-like diuretic

Prototype: Hydrochlorothiazide
Pregnancy Category: D


2.5 mg, 5 mg, 10 mg tablets


Diuretic structurally and pharmacologically similar to hydrochlorothiazide. Diuretic action is associated with interference with transport of sodium ions across renal tubular epithelium. This enhances excretion of sodium, chloride, potassium, bicarbonate, and water.

Therapeutic Effect

Produces a decrease in the systolic and diastolic BPs, and reduces edema in CHF and kidney failure patients.


Management of hypertension as sole agent or to enhance effectiveness of other antihypertensives in severe form of hypertension; also edema associated with CHF and kidney disease.


Anuria, hypokalemia; hepatic coma or precoma; hypersensitivity to metolazone and sulfonamides; SLE; pregnancy (category D), lactation.

Cautious Use

History of gout; elderly; allergies; concomitant use of digitalis glycosides; kidney and liver dysfunction.

Route & Dosage

Adult: PO 5–20 mg/d
Child: PO 0.2–0.4 mg/kg/d divided q12–24h

Adult: PO 2.5–5 mg/d


  • Do not interchange slow availability tablets and rapid availability tablets. They are not equivalent.
  • Schedule doses to avoid nocturia and interrupted sleep. Give early in a.m. after eating to prevent gastric irritation (if given in 2 doses, schedule second dose no later than 3 p.m.).
  • Store at 15°–30° C (59°–86° F) in tightly closed container.

Adverse Effects (≥1%)

GI: Cholestatic jaundice. Body as a Whole: Vertigo, orthostatic hypotension. Hematologic: Venous thrombosis, leukopenia. Metabolic: Dehydration, hypokalemia, hyperuricemia, hyperglycemia.


Drug: Amphotericin B, corticosteroids increase hypokalemic effects; may antagonize hypoglycemic effects of sulfonylureas, insulin; cholestyramine, colestipol decrease thiazide absorption; intensifies hypoglycemic and hypotensive effects of diazoxide; because of increased potassium and magnesium loss, may cause digoxin toxicity; decreases lithium excretion, increasing its toxicity; nsaids may attenuate diuresis—increased risk of nsaid-induced kidney failure.


Absorption: Incomplete; Mykrox has greater absorption. Onset: 1 h. Peak: 2–8 h. Duration: 12–24 h. Distribution: Distributed throughout extracellular tissue; concentrates in kidney; crosses placenta; distributed in breast milk. Metabolism: Does not appear to be metabolized. Elimination: In urine. Half-Life: 14 h.

Nursing Implications

Assessment & Drug Effects

  • Anticipate overdosage and adverse reactions in geriatric patients; may be more sensitive to effects of usual adult dose.
  • Terminate therapy when adverse reactions are moderate to severe.
  • Expect possible antihypertensive effects in 3 or 4 d, but 3–4 wk are required for maximum effect.
  • Lab tests: Determine serum potassium at regular intervals. Prolonged treatment and inadequate potassium intake increase potential for hypokalemia (see Appendix F). Periodic plasma glucose and urinalysis determinations.

Patient & Family Education

  • Do not drink alcohol; it potentiates orthostatic hypotension.
  • Antihypertensive therapy may require as adjunct a high-potassium, low-sodium, and low-calorie diet.
  • Include potassium-rich foods in the diet.
  • Be aware that if hypokalemia develops, dietary potassium supplement of 1000–2000 mg (25–50 mEq) is usually adequate treatment.

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

© 2006-2023 Last Updated On: 02/02/2023 (0)
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