Kinetics and bioavailability of two formulations of amiloride in man.

1. Two formulations of [(14)C]-amiloride were compared in six oedema-free subjects in single-dose (20 mg) studies separated by a two-week interval.2. Calculation of the elimination rate constant (K(e)), half-life (T((1/2))) and apparent volume of distribution (V(d)) from serum and urinary data showed no significant difference between the two formulations. The V(d) values (350 to 380 litres) were greater than total body fluid volume suggesting extravascular sequestration of amiloride.3. Serum and urinary amiloride levels were similar with both formulations. Pharmacokinetic parameters were similar to those of an earlier report based on one formulation.4. The calculated amiloride concentration in the renal distal tubule (3 muM to 20 muM) was similar to, but higher than, reported in vitro concentrations of amiloride which reduced sodium transport in isolated membranes.