Steady-state concentrations and dosage of digoxin in relation to kidney function in hospitalized patients over 70 years of age.

Steady-state serum digoxin concentrations were determined and related to renal function in 62 hospitalized patients 70-93 years of age. Renal function was assessed by serum creatinine concentration, and creatinine clearance was estimated by a formula employing the serum creatinine concentration and adjusting for body weight, sex and age. The steady-state digoxin concentration was inversely related to the estimated creatinine clearance. As there was no correlation between serum creatinine and age, a simplified estimation of creatinine clearance capacity, disregarding age and sex and allowing only for body weight and serum creatinine, was applied. It is suggested that this simplified calculation is suitable for bedside use. If the body weight/serum creatinine ratio is less than 0.5 (kg x 1/mumol), approximately one-third of our patients would have digoxin concentrations that are close to or above the upper reference limit (2.6 nmol l-1) at the maintenance dose of 0.13 mg digoxin daily. A digoxin dose of 0.07 mg daily thus appears to be suitable for many patients aged greater than 70 years when the body weight/serum creatinine ratio is less than 0.5, and also when the serum creatinine level is normal or only slightly elevated. The half-life of digoxin in serum was determined in 12 patients for whom digoxin treatment was withdrawn due to clinical signs of intoxication, and these half-lives were markedly prolonged: 3.5-6 days at a body weight/serum creatinine ratio of 0.5-0.3. The seven patients with prolonged half-lives had serum creatinine concentrations in the range of 80-140 mumol l-1.