How spironolactone works
Spironolactone is an active substance from the class of aldosterone inhibitors (antagonist). It blocks the action of the hormone aldosterone and thus has antihypertensive, antiandrogenic and mild diuretic (diuretic) properties.
The blood is filtered through the renal corpuscle, retaining larger components such as proteins or whole blood cells and filtering out smaller substances such as waste products, but also salts and sugars. The filtrate obtained in this way is called primary urine – about 180 to 200 liters of which are formed every day.
Substances to be excreted, on the other hand, can pass freely. This second filtrate leaves the body as secondary or final urine. The active ingredient spironolactone prevents the hormone aldosterone from binding to docking sites in the cells of the renal tubules.
As a result, less sodium and water are reabsorbed from the primary urine back into the blood, creating and excreting more final urine. The increased fluid excretion also causes blood pressure to drop.
Absorption, degradation and excretion
After ingestion, about 75 percent of spironolactone is rapidly absorbed from the intestine into the blood. It is then largely converted in the liver to another active form called canrenone.
The maximum blood levels of spironolactone are reached about one hour after ingestion, those of the metabolites after about two to three hours. The diuretic effect does not occur immediately, but only after a few days.
When is spironolactone used?
The active substance spironolactone is approved for the treatment of:
- water retention (edema) associated with secondary hyperaldosteronism (e.g., liver cirrhosis with ascites, heart failure, chronic kidney disease, as an adjunct blood pressure medication)
- elevated aldosterone blood levels, which may be clinically manifested by hypertension and low blood potassium levels (primary hyperaldosteronism)
How spironolactone is used
Spironolactone is usually taken in the form of tablets or capsules. The dosage is always determined individually by the doctor depending on the severity of the disease and is also based on the serum potassium concentration.
Normally, treatment is started with 50 to 200 milligrams of spironolactone per day. If the efficacy is insufficient, this dosage can be increased to up to 400 milligrams of active ingredient per day.
What are the side effects of spironolactone?
One in ten to one in a hundred people treated with spironolactone experience spironolactone side effects such as high potassium blood levels, muscle paralysis, high uric acid blood levels with an increased risk of gout attacks, cardiac arrhythmias, sensitivity to touch in the chest and nipples, and breast growth in men (which regresses after discontinuation of the active ingredient).
What should be considered when taking spironolactone?
Contraindications
Spironolactone must not be used in:
- acute renal failure
- anuria (urine volume less than 100 milliliters in 24 hours)
- severe renal dysfunction
- too much potassium in the blood (hyperkalemia)
- too little sodium in the blood (hyponatremia)
Interactions
Non-steroidal anti-inflammatory drugs (e.g. ASA, ibuprofen, indometacin), which are often taken as painkillers, can also lead to increased potassium levels. In addition, they – like the epilepsy drug (antiepileptic) phenytoin – can weaken the effect of spironolactone.
The intake of spironolactone together with the cardiac glycosides digoxin and digitoxin must be strictly monitored by a physician. Increased blood levels of the cardiac glycosides may occur.
Even a slight increase can result in serious side effects (cardiac glycosides have a so-called narrow therapeutic range).
Age restriction
Suitable preparations containing spironolactone can be used from infancy.
Pregnancy and lactation
No data are available on the excretion of spironolactone into breast milk. If an aldosterone antagonist is indeed required, breastfeeding with spironolactone appears to be acceptable.
How to obtain medications containing spironolactone
Medicines containing the active ingredient spironolactone are only available in Germany, Austria and Switzerland from pharmacies with a doctor’s prescription.
Since when has spironolactone been known?
Before the introduction of spironolactone, all diuretics led to increased excretion of potassium. Although potassium deficiency could be counteracted by supplemental potassium administration, alternatives were sought.
In 1959, the active ingredient spironolactone was then tested for the first time and finally approved in 1961.
