Therapeutic Serum Digoxin Concentration: Relation to Age,Weight, Sex,and Serum Creatinine Levels‡‡

Summary: Serum digoxin concentration was determined by radioimmuno-assay in a group of 41 hospitalized adult patients (22 males and 19 females), selected prospectively for constant effective dosage with digoxin for at least three weeks, without clinical or electrocardiographic evidence of digoxin intoxication. Serum creatinine values were within the normal or near-normal range. The majority were receiving diuretic therapy which was associated with mild alkalosis (75% of patients) and occasionally hypomagnesaemia (18%). The patients were considered to be effectively digitalized. The mean serum digoxin concentration six hours after the morning oral dose of digoxin in 28 of the 41 patients, with normal serum creatinine values, was 1.3 ng/ml (S.D. 0.4 ng/ml), and in the other 13 patients with mildly elevated serum creatinine values (range 1.3 to 1.6 mg/dl for 6 males and 1.1 to 1.4 mg/dl for 7 females) was 1.4 ng/ml (S.D. 0.7 ng/ml). Approximate GFR (% of normal corrected for age and surface area) was derived from auto-analyzer serum creatinine values, using the formulae 110/serum creatinine concentration (mg/dl) for males and 85/serum creatinine for females. The patients with mild renal failure (approximate GFR, males 85 to 69% of normal; females, 77 to 61% of normal) were found to be significantly older and required significantly smaller oral maintenance doses of digoxin than the patients with normal serum creatinine valuestoachieve virtually the same serum digoxin concentration. Formulae were derived to enable calculation of the therapeutic daily dose of digoxin from age in years (A), weight in kg (W), sex and serum creatinine concentration in mg/dl (SCr) as follows:—