Pharmacology
Pharmacodynamics
The pharmacodynamics of spironolactone are characterized by high antimineralocorticoid activity, moderate antiandrogenic activity, and weak steroidogenesis inhibition, among other more minor activities. Spironolactone is a prodrug, so most of its actions are actually mediated by its various active metabolites. The major active forms of spironolactone are 7α-thiomethylspironolactone (7α-TMS) and canrenone (7α-desthioacetyl-δ6-spironolactone).Spironolactone is a potent antimineralocorticoid. That is, it is an antagonist of the mineralocorticoid receptor (MR), the biological target of mineralocorticoids like aldosterone and 11-deoxycorticosterone. By blocking the MR, spironolactone inhibits the effects of mineralocorticoids in the body. The antimineralocorticoid activity of spironolactone is responsible for its therapeutic efficacy in the treatment of edema, high blood pressure, heart failure, hyperaldosteronism, and ascites due to cirrhosis. It is also responsible for many of the side effects of spironolactone, such as urinary frequency, dehydration, hyponatremia, low blood pressure, fatigue, dizziness, metabolic acidosis, decreased kidney function, and its risk of hyperkalemia. Due to the antimineralocorticoid activity of spironolactone, levels of aldosterone are significantly increased by the medication, probably reflecting an attempt of the body to maintain homeostasis.Spironolactone is a moderate antiandrogen. That is, it is an antagonist of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT). By blocking the AR, spironolactone inhibits the effects of androgens in the body.
The medication is typically used at high dosages of 100 to 200 mg/day in the treatment of skin and hair conditions in women, and at high dosages of 100 to 400 mg/day in feminizing hormone therapy for transgender women.Spironolactone is available in the form of tablets (25 mg, 50 mg, 100 mg; brand name Aldactone, others) and suspensions (25 mg/5 mL; brand name CaroSpir) for use by mouth. It has also been marketed in the form of 2% and 5% topical cream in Italy for the treatment of acne and hirsutism under the brand name Spiroderm, but this product is no longer available. The medication is also available in combination with other medications, such as hydrochlorothiazide (brand name Aldactazide, others). Spironolactone has poor water solubility, and for this reason, only oral and topical formulations have been developed; other routes of administration such as intravenous injection are not used. The only antimineralocorticoid that is available as a solution for parenteral use is the related medication potassium canrenoate. Contraindications
Contraindications of spironolactone include hyperkalemia (high potassium levels), severe and end-stage kidney disease (due to high hyperkalemia risk, except possibly in those on dialysis), Addisons disease (adrenal insufficiency and low aldosterone levels), and concomitant use of eplerenone. It should also be used with caution in people with some neurological disorders, no urine production, acute kidney injury, or significant impairment of kidney excretory function with risk of hyperkalemia. Side effects
One of the most common side effects of spironolactone is frequent urination.