Key result
Methyldigoxin matches digoxin inotropic potency but triggers arrhythmias at higher concentrations in guinea pig atria.
In isolated guinea pig atria, methyldigoxin produces greater contractility than digoxin at equivalent tissue levels and requires higher concentrations to induce arrhythmias.
May indicate wider therapeutic index for methyldigoxin in atrial tissue; leaves open human translation and clinical relevance.
AbstractThe chronotropic and inotropic effects as well as the tissue levels of digoxin and methyldigoxin were studied in isolated guinea pig atria. Higher concentrations of methyldigoxin than of digoxin were required to cause arrhythmias. The inotropic potencies of the two glycosides did not differ from each another in equimolar concentrations in the organ bath. The increase in contractility correlated with the level of the glycoside in the organ bath and in the tissue. Digoxin was more effectively taken up by the heart tissue than methyldigoxin. Thus, when the tissue levels of the glycosides were the same, the contractility was greater after methyldigoxin than after digoxin.
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Allonen et al. (1977) studied this question. Digoxin and methyldigoxin was evaluated on Chronotropic and inotropic effects, tissue levels, and arrhythmias. In isolated guinea pig atria, digoxin and methyldigoxin showed similar inotropic potencies at equimolar concentrations, but methyldigoxin required higher concentrations to cause arrhythmias.
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