Digoxin metabolism in obesity.

A single intravenous dose of tritiated digoxin was given to five obese patients before and after a mean loss of 102 pounds in weight. There were no significant differences in the blood concentrations of digoxin before and after the weight reduction. Likewise, there were no significant differences in the blood concentrations of digoxin when these data were corrected for fat-free body weight. These findings are consistent with the thesis that fat-free body weight is a more important determinant of the blood concentration of digoxin than total body weight is. The clinical implication of this study is that digoxin dosage may be erroneously high if calculated on the basis of total body weight for obese individuals. DIGOXIN has generally been prescribed in the adult without consideration of body size or weight.' However, Ewy and associates2 found a higher concentration of digoxin in the blood of elderly individuals of smaller body weight than in younger, heavier subjects, after a single intravenous dose of tritiated digoxin. The blood concentrations of digoxin of the two groups were not different when the data were corrected for body weight. It was, therefore, concluded that body weight is an important determinant of blood concentrations of digoxin. Jelliffe3 has likewise stressed the importance of body weight in determining digoxin dosage. Very low concentrations of tritiated digoxin have been found in the adipose tissue in man (JE Doherty: Unpublished observations) and 810 Tritiated digoxin in the dog.4 These findings suggest that lean body weight or fat-free body weight might be more important than total body weight in determining the blood concentration of digoxin. The present study was designed to investigate further the influence of body weight on the blood concentration of digoxin in humans. To obviate the problem of subtle differences of digoxin metabolism among subjects, each obese subject was used as his own control and was studied before and after weight reduction. Methods Five obese subjects, ages 19 to 27 years, were hospitalized in the Clinical Study Unit of the Georgetown University Hospital for studies of change in body composition during dietary weight reduction under the supervision of one of the authors (M.B.).5 Informed consent was obtained from all subjects prior to the initiation of the study. Each subject's medical history was elicited, and physical examination was performed on admission to the hospital.