Drug Groups

approved

Description

A potassium sparing diuretic that acts by antagonism of aldosterone in the distal renal tubules. It is used mainly in the treatment of refractory edema in patients with congestive heart failure, nephrotic syndrome, or hepatic cirrhosis. Its effects on the endocrine system are utilized in the treatments of hirsutism and acne but they can lead to adverse effects. (From Martindale, The Extra Pharmacopoeia, 30th ed, p827)

Indication

Used primarily to treat low-renin hypertension, hypokalemia, and Conn's syndrome.

Pharmacology

Spironolactone is a synthetic 17-lactone steroid which is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics. On its own, spironolactone is only a weak diuretic, but it can be combined with other diuretics. Due to its anti-androgen effect, it can also be used to treat hirsutism, and is a common component in hormone therapy for male-to-female transgendered people. Spironolactone inhibits the effect of aldosterone by competing for intracellular aldosterone receptor in the distal tubule cells. This increases the secretion of water and sodium, while decreasing the excretion of potassium. Spironolactone has a fairly slow onset of action, taking several days to develop and similarly the effect diminishes slowly.

Toxicity

The oral LD₅₀ of spironolactone is greater than 1,000 mg/kg in mice, rats, and rabbits. Acute overdosage of spironolactone may be manifested by drowsiness, mental confusion, maculopapular or erythematous rash, nausea, vomiting, dizziness, or diarrhea. Spironolactone has been shown to be a tumorigen in chronic toxicity studies in rats.

Affected Organisms

Biotransformation

Rapidly and extensively metabolized. The metabolic pathway of spironolactone is complex and can be divided into two main routes: those in which the sulfur moiety is retained and those in which the sulfur moiety is removed by dethioacetylation. Spironolactone is transformed to a reactive metabolite that can inactivate adrenal and testicular cytochrome P450 enzymes. It also has anti-androgenic activity.

Absorption

Fairly rapidly absorbed from the gastrointestinal tract. Food increases the bioavailability of unmetabolized spironolactone by almost 100%.

Half Life

10 minutes

Protein Binding

Spironolactone and its metabolites are more than 90% bound to plasma proteins.

Elimination

The metabolites are excreted primarily in the urine and secondarily in bile.

References

External Links