Effects of phenobarbital on digitoxin and digoxin elimination in the dog

When normal dogs were orally pretreated with a known microsomal enzyme inducer, phenobarbital, the serum biological half-life of digitoxin was not significantly affected, whereas the serum biological half-life of digoxin was significantly shortened by nearly 30%. These results are variant with that previously reported for human beings, wherein microsomal enzyme induction resulted in shortening of plasma biological half-life of digitoxin by more than 40% and insignificant effects on plasma biological half-life of digoxin. Because of the effect on plasma biological half-life, concomitant digoxin and phenobarbital administration to the canine cardiac patient may necessitate careful evaluation of the digitalization.