Orally administered triclabendazole is well absorbed into the bloodstream. It is quickly oxidized in the liver to its sulfoxide derivative, which is also an effective flukicide. Peak plasma levels of the sulfoxide are reached about 1 day after administration. The sulfoxide itself is further metabolized to the sulfone derivative, which is ineffective. Peak plasma levels of the sulfone are reached 3 days after treatment. These two metabolites are usually detected in tissues and milk, whereas the parent molecule remains almost undetectable. Both metabolites bind strongly to plasma proteins, mainly to albumin. The sulfoxide binds reversibly to albumins, and is partly released back in the liver tissues, which increases its bioavailability and the length of its efficacy.
Excretion is achieved mainly through bile and feces (>90%), urine (~2%), and milk (~1%). About 50% of the administered dose is excreted 6 days after treatment.
In ruminants, the slow passage through the complex stomach prolongs the time it can be absorbed. Direct administration into the abomasum (e.g. due to the "oesophageal groove reflex") strongly diminishes the absorption and consequently its efficacy.
Influence of diet. In ruminants, reducing the amount of feed slows down the exit flow of the rumen and prolongs the time the anthelmintic remains there and is absorbed. Consequently it is advisable to reduce the animals' access to feed (especially to fresh pasture, not to water) 24 hours before administration. For the same reason, it is better to keep the animals away from food for about 6 hours after drenching. However sick, weak, or pregnant animals should not be kept away from food and fasting animals should have access to water.