The effects of digoxin and β‐methyldigoxin on the heart rate of decompensated patients with atrial fibrillation

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Abstract
Patients (18) with atrial fibrillation were given digoxin 0.13 mg twice daily for 3 wk and .beta.-methyldigoxin 0.10 mg twice daily for another 3 wk. At the end of each 3 wk period an exercise test was performed and the effects on the heart rate of the 2 drugs were compared. No difference in heart rate was obtained at rest; the heart rate after 6 min of exercise was higher during treatment with digoxin (131 beats/min) than when the patients were taking .beta.-methyldigoxin (124 beats/min). There were no significant differences between digoxin and .beta.-methyldigoxin in their effects on the ECG (R-R intervals, T-wave and Q-T duration). The plasma concentrations of the 2 glycosides were determined by radioimmunoassay and 86Rb- uptake inhibition assay. Comparable plasma concentration values (1.0 ng/ml for digoxin, 1.1 ng/ml for .beta.-methyldigoxin, mean values) were obtained by radioimmunoassay, but the 86Rb-technique gave significantly higher values (mean 1.5 ng/ml) for .beta.-methyldigoxin. .beta.-Methyldigoxin appears to be equal to digoxin for producing slowing of the heart rate in patients with atrial fibrillation.

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