Spironolactone

SPIRONOLACTONE- spironolactone tablet
McKesson Packaging Services Business Unit of McKesson Corporation

WARNING: Spironolactone has been shown to be a tumorigen in chronic toxicity studies in rats (see PRECAUTIONS). Spironolactone should be used only in those conditions described under Indications and Usage. Unnecessary use of this drug should be avoided.

DESCRIPTION

Spironolactone oral tablets contain 25 mg, 50 mg, or 100 mg of the aldosterone antagonist spironolactone, 17-hydroxy-7α-mercapto-3-oxo-17α-pregn-4-ene-21-carboxylic acid ϒ-lactone acetate, which has the following structural formula:

Spironolactone Structural Formula

Spironolactone is practically insoluble in water, soluble in alcohol, and freely soluble in benzene and in chloroform.

Spironolactone tablets, 25 mg contain the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, crospovidone, docusate sodium 85%/sodium benzoate 15%, entrapped peppermint flavor, magnesium stearate, microcrystalline cellulose, sodium starch glycolate.

Spironolactone tablets, 50 mg and 100 mg contain the following inactive ingredients: anhydrous lactose, carnauba wax, colloidal silicon dioxide, docusate sodium 85%/sodium benzoate 15%, entrapped peppermint flavor, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polydextrose, polyethylene glycol, povidone, sodium starch glycolate, titanium dioxide, triacetin.

CLINICAL PHARMACOLOGY

Mechanism of action: Spironolactone is a specific pharmacologic antagonist of aldosterone, acting primarily through competitive binding of receptors at the aldosterone-dependent sodium-potassium exchange site in the distal convoluted renal tubule. Spironolactone causes increased amounts of sodium and water to be excreted, while potassium is retained. Spironolactone acts both as a diuretic and as an antihypertensive drug by this mechanism. It may be given alone or with other diuretic agents which act more proximally in the renal tubule.

Aldosterone antagonist activity: Increased levels of the mineralocorticoid, aldosterone, are present in primary and secondary hyperaldosteronism. Edematous states in which secondary aldosteronism is usually involved include congestive heart failure, hepatic cirrhosis, and the nephrotic syndrome. By competing with aldosterone for receptor sites, spironolactone provides effective therapy for the edema and ascites in those conditions. Spironolactone counteracts secondary aldosteronism induced by the volume depletion and associated sodium loss caused by active diuretic therapy.

Spironolactone is effective in lowering the systolic and diastolic blood pressure in patients with primary hyperaldosteronism. It is also effective in most cases of essential hypertension, despite the fact that aldosterone secretion may be within normal limits in benign essential hypertension.

Through its action in antagonizing the effect of aldosterone, spironolactone inhibits the exchange of sodium for potassium in the distal renal tubule and helps to prevent potassium loss.

Spironolactone has not been demonstrated to elevate serum uric acid, to precipitate gout, or to alter carbohydrate metabolism.

Pharmacokinetics: Spironolactone is rapidly and extensively metabolized. Sulfur-containing products are the predominant metabolites and are thought to be primarily responsible, together with spironolactone, for the therapeutic effects of the drug. The following pharmacokinetic data were obtained from 12 healthy volunteers following the administration of 100 mg of spironolactone (as tablets) daily for 15 days. On the 15th day, spironolactone was taken immediately after a low-fat breakfast and blood was drawn thereafter.

Accumulation Factor:

AUC (0-24 hr, day 15)/

AUC (0-24 hr, day 1)

Mean Peak

Serum Concentration

Mean (SD) Post-Steady

State Half-Life

7-α-(thiomethyl) spirolactone (TMS)

1.25

391 ng/mL at 3.2 hr

13.8 hr (6.4) (terminal)

6-β-hydroxy-7-α-(thiomethyl)
spirolactone (HTMS)

1.50

125 ng/mL at 5.1 hr

15.0 hr (4.0) (terminal)

Canrenone (C)

1.41

181 ng/mL at 4.3 hr

16.5 hr (6.3) (terminal)

Spironolactone

1.30

80 ng/mL at 2.6 hr

Approximately 1.4 hr

The pharmacological activity of spironolactone metabolites in man is not known. However, in the adrenalectomized rat the antimineralocorticoid activities of the metabolites C, TMS, and HTMS, relative to spironolactone, were 1.10, 1.28, and 0.32, respectively. Relative to spironolactone, their binding affinities to the aldosterone receptors in rat kidney slices were 0.19, 0.86, and 0.06, respectively.

In humans the potencies of TMS and 7-α-thiospirolactone in reversing the effects of the synthetic mineralocorticoid, fludrocortisone, on urinary electrolyte composition were 0.33 and 0.26, respectively, relative to spironolactone. However, since the serum concentrations of these steroids were not determined, their incomplete absorption and/or first-pass metabolism could not be ruled out as a reason for their reduced in vivo activities.

Both spironolactone and its metabolites are more than 90% bound to plasma proteins. The metabolites are excreted primarily in the urine and secondarily in bile.

The effect of food on spironolactone absorption (two 100-mg spironolactone tablets) was assessed in a single dose study of 9 healthy, drug-free volunteers. Food increased the bioavailability of unmetabolized spironolactone by almost 100%. The clinical importance of this finding is not known.

INDICATIONS AND USAGE

Spironolactone is indicated in the management of:

Primary hyperaldosteronism for:

Establishing the diagnosis of primary hyperaldosteronism by therapeutic trial.
Short-term preoperative treatment of patients with primary hyperaldosteronism.
Long-term maintenance therapy for patients with discrete aldosterone-producing adrenal adenomas who are judged to be poor operative risks or who decline surgery.
Long-term maintenance therapy for patients with bilateral micro- or macronodular adrenal hyperplasia (idiopathic hyperaldosteronism).

Edematous conditions for patients with:

Congestive heart failure: For the management of edema and sodium retention when the patient is only partially responsive to, or is intolerant of, other therapeutic measures. Spironolactone is also indicated for patients with congestive heart failure taking digitalis when other therapies are considered inappropriate.
Cirrhosis of the liver accompanied by edema and/or ascites: Aldosterone levels may be exceptionally high in this condition. Spironolactone is indicated for maintenance therapy together with bed rest and the restriction of fluid and sodium.
The nephrotic syndrome: For nephrotic patients when treatment of the underlying disease, restriction of fluid and sodium intake, and the use of other diuretics do not provide an adequate response.

Essential hypertension

Usually in combination with other drugs, spironolactone is indicated for patients who cannot be treated adequately with other agents or for whom other agents are considered inappropriate.

Hypokalemia

For the treatment of patients with hypokalemia when other measures are considered inappropriate or inadequate. Spironolactone is also indicated for the prophylaxis of hypokalemia in patients taking digitalis when other measures are considered inadequate or inappropriate.

Usage in Pregnancy. The routine use of diuretics in an otherwise healthy woman is inappropriate and exposes mother and fetus to unnecessary hazard. Diuretics do not prevent development of toxemia of pregnancy, and there is no satisfactory evidence that they are useful in the treatment of developing toxemia.

Edema during pregnancy may arise from pathologic causes or from the physiologic and mechanical consequences of pregnancy.

Spironolactone is indicated in pregnancy when edema is due to pathologic causes just as it is in the absence of pregnancy (however, see PRECAUTIONS: Pregnancy). Dependent edema in pregnancy, resulting from restriction of venous return by the expanded uterus, is properly treated through elevation of the lower extremities and use of support hose; use of diuretics to lower intravascular volume in this case is unsupported and unnecessary. There is hypervolemia during normal pregnancy which is not harmful to either the fetus or the mother (in the absence of cardiovascular disease), but which is associated with edema, including generalized edema, in the majority of pregnant women. If this edema produces discomfort, increased recumbency will often provide relief. In rare instances, this edema may cause extreme discomfort which is not relieved by rest. In these cases, a short course of diuretics may provide relief and may be appropriate.

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