Potassium sparing diuretics
Triamterene and amiloride are the only drugs of this class in clinical use. They are weak diuretics and mostly used for their antikaluric action in combination with other diuretics. Several combination tablets with thiazides are available. They act in the distal tubules and collecting duct, where they inhibit the Na+-/K+ exchange.
The potassium sparing diuretics bind to the luminal sodium channels, thereby inhibiting the Na+ ion influx. The blockade of the sodium channels reduces the lumen negative transepithelial voltage. Normally this potential difference facilitates cation excretion. The reduced lumen negative voltage decreases excretion of K+ and H+ ions, and other cations such as Ca2+ and Mg2+.
Hyperkalemia is the most serious adverse effect and consequently the main contraindication. Symptoms of side effects are GI complaints (nausea, vomiting, diarrhea), leg cramps, weakness, headache, and dizziness.
Amiloride can cause:
Extra info: Amiloride reduces negative lumen voltage, thereby decreasing excretion of K+ and H+ ions.