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Spironolactone

Pronunciation: (spir-ON-oh-LAK-tone)
Class: Potassium-sparing diuretic

Trade Names:
Aldactone
- Tablets 25 mg
- Tablets 50 mg
- Tablets 100 mg

Novo-Spiroton (Canada)

Pharmacology

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Competitively inhibits aldosterone in distal tubules, resulting in increased excretion of sodium and water and decreased excretion of potassium.

Pharmacokinetics

Absorption

Spironolactone is rapidly and extensively metabolized. Food increases bioavailability by almost 100%. Following a 100 mg dose, mean C _max is 80 ng/mL; T _max is 2.6 h.

Distribution

Spironolactone is more than 90% bound to plasma proteins.

Metabolism

Sulfur-containing products are predominant metabolites and are thought to be primarily responsible together with spironolactone for the therapeutic effect of the drug.

Elimination

Metabolites are excreted primarily in the urine and secondarily in bile. Half-life is approximately 1.4 h.

Indications and Usage

Short-term preoperative treatment of primary hyperaldosteronism; long-term maintenance therapy for idiopathic hyperaldosteronism; management of edematous conditions in CHF, cirrhosis of liver, and nephrotic syndrome; essential hypertension; treatment of hypokalemia; long-term maintenance therapy for patients with discrete aldosterone-producing adrenal adenomas; increase survival and reduce need for hospitalization for severe heart failure (New York Heart Association [NYHA] class III to IV).

Unlabeled Uses

Treatment of hirsutism in women.

Contraindications

Acute renal insufficiency; anuria; hyperkalemia; impaired renal excretory function.

Dosage and Administration

Diagnosis of Primary Hyperaldosteronism
Adults

PO 400 mg/day for 4 days (short test) or 3 to 4 wk (long test).

Maintenance Therapy for Hyperaldosteronism
Adults

PO 100 to 400 mg daily in single or divided doses.

Edema (CHF, hepatic cirrhosis, or nephrotic syndrome)
Adults

PO 25 to 200 mg/day in single or divided doses.

Essential Hypertension
Adults

PO 50 to 100 mg/day in single or divided doses.

Diuretic-Induced Hypokalemia
Adults

PO 25 to 100 mg/day when oral potassium or other potassium-sparing regimens are inappropriate.

Severe Heart Failure (NYHA class III to IV)
Adults

PO Start with 25 mg once daily if serum potassium is 5 mEq/L or less and serum creatinine is 2.5 mg/dL or less. Dosage may be increased to 50 mg once daily if indicated in patients who tolerate 25 mg/day. Patients who do not tolerate 25 mg/day may have their dosage decreased to 25 mg every other day.

Storage/Stability

Store tablets below 77°F.

Drug Interactions

ACE inhibitors

May result in severely elevated serum potassium levels.

Alcohol, barbiturates, narcotics

Orthostatic hypotension may be potentiated.

Angiotensin II receptor antagonists (eg, candesartan, losartan, telmisartan)

Risk of hyperkalemia, especially in patients with renal impairment or type 2 diabetes, may be increased.

Corticosteroids

Increased risk of electrolyte depletion, particularly hypokalemia.

Digitalis glycosides

May decrease digoxin clearance, resulting in increased serum digoxin levels and toxicity; may attenuate inotropic action of digoxin.

Diuretics

Risk of dilutional hyponatremia may be increased.

Mitotane

May decrease therapeutic response to mitotane.

Salicylates

May result in decreased diuretic effect.

Lithium

Lithium clearance may be reduced, increasing the risk of toxicity.

Nondepolarizing muscle relaxants (eg, tubocurarine)

Increased responsiveness to muscle relaxant effect may occur.

NSAIDs (eg, indomethacin)

Risk of severe hyperkalemia may be increased.

Potassium preparations

May severely increase serum potassium levels, possibly resulting in cardiac arrhythmias or cardiac arrest. Do not take with potassium preparations.

Pressor amines (eg, norepinephrine)

Vascular responsiveness to norepinephrine may be decreased. Use with caution in patients receiving regional or general anesthesia.

Laboratory Test Interactions

Drug may cause falsely elevated serum digoxin values with radioimmunoassay (assay specific) for measuring digoxin.

Adverse Reactions

Cardiovascular

Vasculitis.

CNS

Ataxia; drowsiness; headache; lethargy; mental confusion.

Dermatologic

Erythematous or maculopapular cutaneous eruptions; urticaria.

GI

Cramping; diarrhea; gastritis; GI bleeding; nausea; ulceration; vomiting.

Genitourinary

Amenorrhea; breast carcinoma; gynecomastia; inability to achieve or maintain an erection; irregular menses; postmenopausal bleeding.

Hematologic-Lymphatic

Agranulocytosis.

Hepatic

Mixed cholestatic/hepatocellular toxicity.

Hypersensitivity

Anaphylactic reactions.

Metabolic-Nutritional

Hyperkalemia.

Renal

Renal dysfunction including renal failure

Miscellaneous

Fever.

Precautions

Warnings

Spironolactone has been shown to be tumorogenic in chronic toxicity studies in rats. The drug should only be used for conditions included under indications and usage. Unnecessary use of the drug should be avoided. Monitor for evidence of fluid or electrolyte imbalance (eg, alkalosis, hyperkalemia, hypomagnesemia, hyponatremia). Monitoring serum and urine electrolytes are especially important when the patient is vomiting excessively or receiving parenteral fluids. Obtain ECG if hyperkalemia is suspected.

Monitor

Periodically measure serum electrolytes to detect possible electrolyte imbalance, particularly in the elderly and in patients with renal or hepatic impairment. It is critical to monitor serum potassium in patients with severe heart failure; monitor potassium and creatine 1 wk after starting therapy, monthly for the first 3 mo, then quarterly for a year, and then every 6 mo.

Pregnancy

Category D .

Lactation

Excreted in breast milk.

Children

Safety and efficacy not established.

Renal Function

Contraindicated in patients with anuria, acute renal insufficiency, and/or significant impairment of renal excretory function. Transient elevation of BUN may occur, particularly in patients with preexisting renal impairment.

Hepatic Function

Use with caution because minor alterations in fluid and electrolyte balance may precipitate hepatic coma.

Acidosis

Reversible hyperchloremic metabolic acidosis, usually in association with hyperkalemia, has been reported in patients with decompensated hepatic cirrhosis.

Electrolyte imbalances and BUN increase

Hyperkalemia (serum potassium more than 5.5 mEq/L), hyponatremia, hypochloremia, and increases in BUN may occur.

Gynecomastia

Gynecomastia, related to both dose and duration of treatment, may occur.

Severe heart failure

Hyperkalemia may be fatal. Discontinue or interrupt treatment for serum potassium more than 5 mEq/L or serum creatine more than 4 mg/dL.

Overdosage

Symptoms

Diarrhea, dizziness, drowsiness, mental confusion, maculopapular or erythematous rash, nausea, vomiting.

In patients with severe liver disease

Hepatic coma, hyperkalemia, hyponatremia.

In patients with renal function impairment

Hyperkalemia.

Patient Information

Explain that medication's full diuretic effect may not be achieved for 1 to 2 wk.
Instruct patient to avoid taking potassium supplements and large quantities of potassium-rich foods or potassium salt substitutes.
For patient being treated for hypertension, explain that patient may feel tired for several weeks because body needs to adjust to lowered BP.
Instruct patient to take drug with food to minimize GI irritation.
Tell patient to weigh self twice weekly and to notify health care provider of any increase.
Instruct patient to notify health care provider if new symptoms develop.
Tell patient to report these symptoms to health care provider: GI cramping, diarrhea, lethargy, thirst, headache, skin rash, menstrual abnormalities, deepening of voice, and breast enlargement in men.
Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.