A-Z Drug Facts > Metolazone

Metolazone

Pronouncation: (meh-TOLE-uh-ZONE)
Class: Thiazide diuretic

Trade Names:
Zaroxolyn
- Tablets 2.5 mg
- Tablets 5 mg
- Tablets 10 mg

Trade Names:
Mykrox
- Tablets 0.5 mg

Pharmacology

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Increases urinary excretion of sodium and chloride by inhibiting reabsorption in ascending limb of loop of Henle and early distal tubules.

Pharmacokinetics

Absorption

Steady states are usually reached in 4 to 5 days with 65% absorbed. T _max is approximately 8 h (2 to 4 h for Mykrox ); C _max is 0.5 to 2 mg (dose dependent for Mykrox ).

Metabolism

A small fraction of metolazone is metabolized.

Elimination

Most is excreted in the unconcentrated form in urine. The t _½ is approximately 14 h.

Onset

Onset is 1 h.

Peak

Time to peak is 2 h.

Duration

Duration is 12 to 24 h.

Indications and Usage

Treatment of edema and hypertension.

Unlabeled Uses

Prevention of calcium nephrolithiasis; reduction of postmenopausal osteoporosis; reduction of urine volume in diabetes insipidus.

Contraindications

Anuria; renal decompensation; hepatic coma or precoma.

Dosage and Administration

Adults

PO 0.5 to 1 mg/day ( Mykrox ) or 2.5 to 20 mg/day ( Zaroxolyn ). Do not interchange Mykrox with Zaroxolyn . Mykrox is absorbed more rapidly and completely than Zaroxolyn .

Storage/Stability

Store at room temperature (59° to 86°F) in tight, light-resistant container.

Drug Interactions

Cholestyramine, colestipol

May decrease effects of metolazone by decreasing absorption.

Diazoxide

Concurrent use may produce severe hyperglycemia.

Digitalis glycosides (eg, digoxin)

Urinary loss of potassium and magnesium may predispose patient to digitalis-induced arrhythmia.

Lithium

Metolazone may decrease renal elimination of lithium, resulting in toxicity.

Loop diuretics (eg, furosemide)

Concurrent use may produce profound diuresis and electrolyte abnormalities.

Sulfonylureas (eg, tolbutamide)

Metolazone may decrease hypoglycemic effect of sulfonylureas by increasing blood glucose.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Rapid-acting formulation

Orthostatic hypotension; palpitations; chest pain; cold extremities; edema.

Slow-acting formulation

Venous thrombosis, palpitations; chest pain; excessive volume depletion; hemoconcentration.

CNS

Rapid-acting formulation

Dizziness; headache; weakness; “weird” feeling; neuropathy; fatigue; lethargy; lassitude; depression.

Slow-acting formulation

Dizziness; syncope; neuropathy; vertigo; headache; weakness; fatigue; lethargy; lassitude; anxiety; depression; nervousness.

Dermatologic

Rapid-acting formulation

Necrotizing angiitis; vasculitis; cutaneous vasculitis; dry skin.

Slow-acting formulation

Photosensitivity; necrotizing angiitis; vasculitis; cutaneous vasculitis.

EENT

Bitter taste.

GI

Rapid-acting formulation

Nausea.

Slow-acting formulation

Nausea; anorexia; pancreatitis.

Genitourinary

Slow-acting formulation

Impotence.

Hematologic

Slow-acting formulation

Leukopenia; agranulocytosis; aplastic anemia.

Hepatic

Slow-acting formulation

Jaundice; hepatitis.

Metabolic

Hypokalemia; hyperuricemia; hyponatremia; hypochloremia; hypochloremic alkalosis.

Respiratory

Rapid-acting formulation

Cough; epistaxis; sinus congestion; sore throat.

Miscellaneous

Rapid-acting formulation

Impotence; joint pain; back pain; itching eyes; tinnitus; muscle cramps and spasms.

Slow-acting formulation

Swelling; chills; acute gouty attack; hyperglycemia; glucosuria; muscle cramps and spasms.

Precautions

Pregnancy

Category B .

Lactation

Undetermined.

Children

Not recommended for use in children.

Hypersensitivity

May occur; cross-sensitivity to sulfonamides or thiazides possible.

Renal Function

May precipitate azotemia; use drug with caution.

Hepatic Function

May precipitate hepatic coma; use drug with caution.

Tartrazine Sensitivity

Some products contain tartrazine, which may cause allergic-type reactions (eg, bronchial asthma).

Fluid and electrolytes

May be altered; periodic determinations of serum electrolytes, BUN, uric acid, and glucose are indicated.

Hyperuricemia

May increase serum uric acid and precipitate gout.

Lipids

May cause increases in total serum cholesterol, triglycerides, and LDL.

Lupus erythematosus

May be activated or exacerbated.

Postsympathectomy patients

Antihypertensive effects may be increased.

Overdosage

Symptoms

Orthostatic hypotension, syncope, lethargy, GI hypermotility, dizziness, electrolyte abnormalities, CNS depression, drowsiness, hemoconcentration, GI irritation.

Patient Information

• Advise patient to take early in day to avoid sleep disruption.
• Tell patient to take with food if stomach upset occurs.
• Explain significance of potential potassium loss, and identify appropriate supplemental food sources (eg, bananas, orange juice, dates, citrus fruits, apricots). Teach patient signs and symptoms of hypokalemia (muscle weakness, cramping).
• Explain that dizziness or lightheadedness may occur if patient stands up too fast.
• Tell patient to avoid exposure to sunlight and to use sunscreen or wear protective clothing until tolerance to sunlight can be established.
• Explain that BP should be checked periodically by patient or family member.
• Review signs and symptoms of fluid imbalance.

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