Mechanism of Action
Amiloride works by directly blocking the epithelial sodium channel (ENaC) thereby inhibiting sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the kidneys (this mechanism is the same for triamterene). This promotes the loss of sodium and water from the body, but without depleting potassium. The drug is often used in conjunction with thiazide (e.g. co-amilozide) or loop diuretics (e.g. co-amilofruse). Due to its potassium-sparing capacities, hyperkalemia (high blood potassium levels) is occasionally observed in patients taking amiloride. The risk is high in concurrent use of ACE inhibitors or spironolactone. Patients are also advised not to use potassium-containing salt replacements. Amiloride also carries the risk of developing an acidosis.
A fraction of the effects of amiloride is inhibition of cyclic GMP-gated cation channels in the inner medullary collecting duct.
Amiloride has a second action on the heart, blocking Na+/H+ exchangers Sodium-hydrogen antiporter 1 or NHE-1. This minimizes reperfusion injury in ischemic attacks.
Acid-sensing ion channels (ASICs) are also sensitive to inhibition by amiloride. ASICs are involved in nociceptor responses to pH.
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