Amiloride HCl, the active ingredient in Midamor, directly targets the epithelial sodium channels (ENaCs) in the distal tubules and collecting ducts of the kidneys. It blocks these channels, preventing sodium reabsorption.
Sodium Reabsorption Inhibition
This sodium blockage has a cascading effect. By inhibiting sodium reabsorption, amiloride increases sodium excretion in the urine. Consequently, it also reduces potassium excretion, leading to increased potassium retention within the body.
Impact on Potassium and Hydrogen Ions
The mechanism also influences hydrogen ion excretion. Reduced sodium reabsorption indirectly affects the body’s acid-base balance. Amiloride’s inhibition of sodium channels can increase the excretion of hydrogen ions, slightly alkalizing the urine.
Clinical Significance: Potassium-Sparing Diuretic
This mechanism is why amiloride is classified as a potassium-sparing diuretic. Unlike other diuretics that promote potassium loss, amiloride helps retain potassium, minimizing the risk of hypokalemia (low potassium levels), a significant side effect of many other diuretics.
Pharmacokinetic Considerations
| Absorption | Amiloride is poorly absorbed orally. |
| Metabolism | It’s minimally metabolized. |
| Excretion | Primarily excreted unchanged via the kidneys. |
Potential Drug Interactions
Because of its effects on potassium levels, amiloride can interact with other medications that also affect potassium levels, such as ACE inhibitors and potassium supplements. Careful monitoring is needed when using amiloride concurrently with such medications.
