β-Methyl-digoxin

Summary

In guinea pigs under urethane anaesthesia the concentrations of radioactivity in the plasma, the liver and the heart and the protein binding of radioactivity were measured 1 h after the intravenous injection of 0.2 μmoles/kg β-methyldigoxin or digoxin. The distribution coefficients were calculated between the concentrations in the plasma water and the tissues. Apart from a slightly higher distribution coefficient for β-methyl-digoxin than for digoxin between liver and plasma water there was no significant difference between the two glycosides.

In guinea pigs under barbital anaesthesia, cardiac failure was produced by additional doses of barbital-Na. Bemegride was given to counteract the effects of barbital on the vasomotor centre. β-Methyl-digoxin and digoxin were infused until cardiac arrest. For each animal the doses were calculated which led to an increase in cardiac performance by 50 g · cm/sec, arrhythmia, ventricular fibrillation or cardiac arrest. The therapeutic range was calculated from the doses producing arrhythmias and those increasing cardiac performance by 50 g · cm/sec (“therapeutic” dose).

There was no difference between the “therapeutic” and toxic doses and the therapeutic ratios of β-methyl-digoxin and digoxin.