Closantel is a member of the salicylanilide class of anthelmintics. Salicylanilides are hydrogen (proton) ionophores (referred to as oxidative phosphorylase uncouplers.)

The chemical structure of salicylanilides illustrate the possession of a detachable proton. This type of molecule is lipophilic and is known to shuttle protons across membranes, in particular the inner mitochondrial membrane. Closantel acts by uncoupling oxidative phosphorylation.

Closantel is a parasiticide with activity against fluke.

After topical administration of the product to cattle at a dose rate of 20 mg closantel per kg the following parameters were observed: Closantel – Cmax of 57 (SD ± 52) µg/mL, AUC of 34690 (SD ± 29922) µg/hr/mL, Tmax of 223 (SD ± 327) hours (median value) and t½ of 385 (SD ± 95) hours (harmonic mean).

Salicylanilides are poorly metabolised and are excreted mainly unchanged. About 90% of closantel is excreted unchanged in the faeces and urine in cattle.

See sections, "Special precautions for use" and "Special precautions for the disposal of unused veterinary medicinal product or waste materials derived from the use of such products".