In comparison, the ENaC inhibitor triamterene is metabolized by the liver. Excretion
About 50% of amiloride is excreted unchanged by the kidneys, while around 40% is excreted in the feces (likely drug that wasnt absorbed). The half-life of amiloride in humans is between 6 and 9 hours, which may be prolonged in people with poor kidney function. Pharmacogenomics
A single nucleotide polymorphism (SNP) in the protein NEDD4L may impact how amiloride affects a persons blood pressure in people with high blood pressure. Chemistry
Amiloride is a pyrazinoylguanidine, composed of a substituted pyrazine ring structure with a carbonylguanidinium substituent. Amilorides pKa is 8.67, which is due to the guanidinium group. In high pH (alkaline, low hydrogen concentration) environments, the guanidinium group is deprotonated and the compound is rendered neutral, depleting its activity on sodium channels. Amiloride, as a pure substance, is highly fluorescent, with excitation wavelengths at 215, 288, and 360 nm, emitting light at 420 nm. History
Amiloride was first synthesized and discovered by the Merck Sharp and Dohme Research Laboratories in the late 1960s. The drug was discovered as part of a screening process of chemicals that reversed the effects of mineralocorticoids in vivo. Amiloride was the only drug in the screen that was capable of causing the excretion of sodium (natriuresis) without a concomitant urinary excretion of potassium (kaliuresis). Thousands of amiloride analogues have been studied since its initial discovery, which have been used to study the effects of sodium transporters.Amiloride was approved by the U.S. Food and Drug Administration (FDA) on October 5, 1981.
It is unknown if amiloride can be dialyzed off, and no specific antidote against it exists. Treatment is generally supportive, though hyperkalemia can be treated. Interactions
Amiloride may have important drug-drug interactions when combined with other medications that also increase potassium levels in the blood, leading to hyperkalemia. For example, the combination of amiloride with angiotensin-converting enzyme (ACE) inhibitors like lisinopril, or angiotensin II receptor type 1 (AT1) antagonists like losartan, may lead to high levels of potassium in the blood, requiring frequent monitoring. Pharmacology
Mechanism of action
Diuresis
Amiloride works by directly blocking the epithelial sodium channel (ENaC) with an IC50 around 0.1 μM, indicating potent blockade. Antagonism of ENaC thereby inhibits sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the nephron. This promotes the loss of sodium and water from the body, and reduces potassium excretion. The drug is often used in conjunction with a thiazide diuretic to counteract with a potassium-losing effect. Due to its potassium-sparing capacities, hyperkalemia (elevated potassium concentration in the blood) can occur. The risk of developing hyperkalemia is increased in patients who are also taking ACE inhibitors, angiotensin II receptor antagonists, other potassium-sparing diuretics, or any potassium-containing supplements. Miscellaneous
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.