Digoxin dosage in renal insufficiency: impracticality of basing it on the creatinine clearance, body weight and volume of distribution.

Previous dosing schedules for digoxin in renal failure have considered the decrease in the elimination rate constant but not the decrease in the volume of distribution. A dosing schedule based on the creatinine clearance, body weight and volume of distribution has been developed from pharmacokinetic data taken from the literature. Its validity was tested in a clinical study of 35 patients with chronic renal insufficiency not requiring dialysis. The dosing schedule resulted in correct digitalization expressed as a steady state plasma digoxin concentration in the therapeutic range (0.5-2.0 ng/ml) in 25 out of 27 patients (93%). However, of 82 possible candidates for the study, it could not be performed in 47 (57%). The high drop-out rate was mainly due to the complicated dosing schedule and to the difficulty of repeatedly measuring creatinine clearance on a routine basis. Therefore, safe dosing of digoxin in renal insufficiency does not seem to be feasible in practice. Digitoxin may be a better alternative.