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.

Indications
Potassium-sparing diuretics are generally used in combination with other diuretic drugs (e.g. loop diuretics) that would otherwise tend to lower the potassium levels to potentially dangerous low levels (hypokalemia). The combination therefore helps maintain a normal reference range for potassium.

Adverse effects
On their own this group of drugs may raise potassium levels beyond the normal range, termed hyperkalemia, which risks potentially fatal arrhythmias.

Mechanism of action
The potassium-sparing diuretics are competitive antagonists that either compete with aldosterone for intracellular cytoplasmic receptor sites, or directly block sodium channels (specifically epithelial sodium channels (ENaC) by amiloride). The former prevents the production of proteins that are normally synthesized in reaction to aldosterone. These mediator proteins are not produced, and so stimulation of sodium-potassium exchange sites in the collection tubule does not occur. This prevents sodium re-absorption and potassium and hydrogen ion secretion.

Chemical structure
Potassium-sparing diuretics do not share any obvious chemical similarities, except for the steroid-structure of the aldosterone antagonists. Those in clinical use include:
 * Epithelial sodium channel blockers
 * Amiloride
 * Triamterene
 * Aldosterone antagonists:
 * Spironolactone
 * Eplerenone

Other Diuretics
While not classically considered potassium-sparing diuretics, ACE inhibitors (ACEi) and angiotensin receptor blockers (ARB) are anti-hypertensive drugs with diuretic effects that decrease renal excretion of potassium. They work by inhibiting either the production (ACEis) or effects (ARBs) of angiotensin 2. This results in a decrease in aldosterone release, which causes potassium-sparing-diuretic-like effects similar to those of the aldosterone antagonists, spironolactone and eplerenone.