Cat assay for the emetic action of digitalis and related glycosides (digitoxin, digoxin, lanatoside C, ouabain and calactin)

1. A titration assay with two end points is described for comparison of the emetic and lethal potencies of digitalis-like drugs.2. A drug was infused at constant rate to a conscious, unrestrained cat, through an indwelling venous cannula. At the moment of vomiting the cat was rapidly anaesthetized and infusion continued at the same rate until the moment of cardiac arrest.3. With very slow and very fast infusions, the emetic and lethal doses tended to rise. In the range between these extremes (which varied from drug to drug) they were independent of time.4. The observations could be accounted for by analogue computation, assuming that the drugs entered an initial pool and were distributed at finite rates to receptors in the CNS (vomiting centre) and heart.5. Half times of metabolic loss derived from this computation for digitoxin, digoxin and ouabain (17, 9.9 and 1.8 h, respectively) were in the same ratio as the threefold longer half times reported for these drugs in man.6. When measured with infusion rates in the time independent range, the ratio of lethal to emetic doses did not vary between the drugs studied. All caused vomiting at 40% of the lethal dose.7. From a review of the literature, the emetic and cardiotoxic actions of digitalis-like drugs appear inseparable and probably share a common biochemical mechanism.8. It is concluded that foreseeable improvements in digitalis-like drugs are small and would depend on the elimination of any local emetic effect on gut receptors which they may have.