Spironolactone commonly referred to as simply spiro, is a diuretic

Diuretic

A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...

 and is used as an antiandrogen

Antiandrogen

Antiandrogens, or androgen antagonists, first discovered in the 1960s, prevent androgens from expressing their biological effects on responsive tissues. Antiandrogens alter the androgen pathway by blocking the appropriate receptors, competing for binding sites on the cell's surface, or affecting...

.

It is a synthetic 17-lactone

Lactone

In chemistry, a lactone is a cyclic ester which can be seen as the condensation product of an alcohol group -OH and a carboxylic acid group -COOH in the same molecule...

 drug that is a renal competitive aldosterone antagonist

Aldosterone antagonist

Aldosterone antagonist refers to diuretic drugs which antagonize the action of aldosterone at mineralocorticoid receptors. This group of drugs is often used as adjunctive therapy, in combination with other drugs, for the management of chronic heart failure...

 in a class of pharmaceuticals called potassium-sparing diuretic

Potassium-sparing diuretic

Potassium-sparing diuretics are diuretic drugs that do not promote the secretion of potassium into the urine.They are used as adjunctive therapy, together with other drugs, in the treatment of hypertension and management of congestive heart failure....

s, used primarily to treat heart failure, ascites

Ascites

Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...

 in patients with liver disease, low-renin

Renin

Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...

 hypertension

Hypertension

Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

, hypokalemia

Hypokalemia

Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...

, secondary hyperaldosteronism (such as occurs with hepatic cirrhosis), and Conn's syndrome

Conn's syndrome

Primary aldosteronism, also known as primary hyperaldosteronism, is characterized by the overproduction of the mineralocorticoid hormone aldosterone by the adrenal glands., when not a result of excessive renin secretion. Aldosterone causes increase in sodium and water retention and potassium...

 (primary hyperaldosteronism).