Amiloride exhibits poor oral bioavailability, typically ranging from 5% to 15%. This low absorption is primarily attributed to its extensive first-pass metabolism in the liver and incomplete gastrointestinal absorption.
Following oral administration, peak plasma concentrations are usually observed within 2 to 6 hours. Intravenous administration bypasses the first-pass effect, resulting in significantly higher bioavailability.
Amiloride distributes minimally into tissues, with a relatively small volume of distribution (approximately 0.2 L/kg). It does not readily cross the blood-brain barrier or the placental barrier, limiting its central nervous system effects and minimizing fetal exposure.
Amiloride undergoes minimal metabolism. Renal excretion is the primary route of elimination, with approximately 60% to 80% of an administered dose being recovered unchanged in the urine within 24 hours. This primarily occurs through glomerular filtration and active tubular secretion. The remainder is likely eliminated through biliary excretion.
The elimination half-life of amiloride is generally considered to be around 6 to 10 hours, although this can vary depending on renal function. Patients with impaired renal function will experience prolonged half-lives and increased drug accumulation.
| Oral Bioavailability | 5-15% |
| Time to Peak Plasma Concentration (oral) | 2-6 hours |
| Volume of Distribution | ~0.2 L/kg |
| Metabolism | Minimal |
| Excretion | Primarily renal (60-80% unchanged in urine) |
| Elimination Half-life | 6-10 hours (renal function dependent) |
Careful consideration of renal function is crucial when prescribing amiloride, particularly for patients with impaired renal function or those receiving concomitant medications affecting renal clearance.
