Clinical implications of serum digoxin concentrations.

Factors influencing serum digoxin concentrations, and the relation of these levels to classical electrocardiographic (ECG) and clinical manifestations of toxicity, were assessed in a series of 463 consecutively hospitalized patients of mean age 58 years. The majority of patients were receiving beta-acetyldigoxin or beta-methyldigoxin. Age, sex, creatinine clearance, and weight-corrected dose collectively explained less than 7% of overall variability in serum digoxin concentrations; creatinine clearance, which declined significantly with age (r=-0.36, p less than 0.001) was the most important of these determinants. ST-segment depression was present in the majority of patients and became more common at higher serum digoxin concentrations. However, PR interval, QRS durations, QT interval, or the presence of AV block were not associated with serum levels. Among 75 patients with atrial fibrillation, ventricular rate did not decline with increasing digoxin concentrations. The presence of gastrointestinal, neuromuscular, or psychiatric symptoms classically attributed to digitalis toxicity was not associated with serum digoxin concentration. Serum levels of digoxin appear to be of limited value in assessing the degree of digitalization.