Comparative pharmacokinetics of coumarin anticoagulants. XLII: Effect of phenobarbital on systemic availability of orally administered dicumarol in rats with ligated bile ducts.

The purpose of this investigation was to determine if the previously demonstrated inhibitory effect of phenobarbital treatment on the systemic availability of orally administered dicumarol in rats is related to the known effect of phenobarbital on bile output. It was found that phenobarbital had no apparent effect on the systemic availability of an aqueous dicumarol suspension in rats with ligated bile ducts. Compared to results obtained previously on normal rats, bile duct-ligated rats absorbed and eliminated dicumarol much more slowly and absorbed much less of the anticoagulant. On the other hand, the relative inductive effect of phenobarbital treatment on dicumarol elimination was similar in normal and in bile duct-ligated animals. The latter exhibited substantial serum transaminase elevations, indicative of liver damage presumably secondary to cholestasis. These results demonstrate that a drug-drug interaction can depend markedly on the pathophysiological status of the animals.