Comparative pharmacodynamics of betamethyl digoxin and digoxin in man

The positive inotropic effects and serum glycoside levels following intravenous and oral administration of betamethyl digoxin (BMD) were measured and compared with those of digoxin in normal adults. The cardiac inotropy was assessed noninvasively in the abbreviation of the electromechanical systolic index (QS2I) obtained by serial measurements of systolic time intervals. Following 0.8 mg BMD intravenously, the QS2I abbreviation occurred within 3 min and reached a maximum at 4 hr. The time-course and the magnitude of the response were essentially the same as those obtained with 0.8 mg digoxin given intravenously in the same subjects. The serum glycoside levels were also similar for both drugs. When administered orally the QS2I abbreviation to 0.8 mg BMD appeared at 40 min and reached a maximum at 4 hr. The time-course and the magnitude of the effects were similar to those observed following oral digoxin. The blood digitalis levels following the drug ingestion, however, were significantly higher for BMD than for digoxin which suggests greater gastrointestinal absorption of BMD. Based on our observations, the inotropic effects of BMD are similar to those of digoxin. Our results, however, do not demonstrate greater cardiac activity after oral administration of BMD despite higher blood levels.