A compound of the formula (I) e.g. N-[1-cyano-1-(5-cyano-2,3-dihydro-1-benzofuran-2-yl)ethyl]-4-[(trifluoromethyl)thio]benzamideor a tautomer thereof, or a pharmaceutically acceptable salt of said compound, tautomer, wherein: X is O or S and the other substituents are defined in the specification. Further disclosed is the use of the compound of formula (I) in the preparation of a medicament for the treatment of a parasitic infestation in a host animal, and a method of treatment of a parasitic infestation in a host animal, wherein the host animal is a non-human animal. Also disclosed is a pharmaceutical composition comprising a compound of formula (I).
