Plasma kinetics of digoxin in the cat.

The biological half-life of digoxin was 33.3 +/- 9.5 hours in 6 cats after a single IV injection. Longer half-lives were obtained after chronic oral administration, indicating that digoxin elimination is capacity-limited in the cat. The mean percentage of urinary excretion of digoxin after a single IV dose was 45% +/- 9.7% over a 10-day period. Toxic plasma concentrations ranged from 2.4 to 2.9 ng/ml, and 5 of 6 cats had clinical signs of toxicosis at concentrations greater than 2.6 ng/ml. Prolongation of the PQ interval was seen on the ECG at nontoxic plasma concentrations in 4 of 6 cats. The most striking ECG evidence of digoxin toxicosis was ST-segment elevation seen in 3 of the 6 cats.