A pharmaceutical composition comprising an isoxazoline compound of formula Wherein R 1 = halogen, CF 3, OCF 3, CN, n = integer from 0 to 3, preferably 1, 2 or 3, R 2 = C 1 -C 3 -haloalkyl, preferably CF 3 or CF 2 Cl, T = 5- or 6-membered ring, which is optionally substituted by one or more radicals Y, Y = methyl, halomethyl, halogen, CN, NO 2, NH 2 -C=S, or two adjacent radicals Y form together a chain, especially a three or four membered chain; Q = X-NR 3 R 4 or a 5-membered N-heteroaryl ring, which is optionally substituted by one or more radicals; X = CH 2, CH(CH 3), CH, CO, CS, R 3 = hydrogen, methyl, haloethyl, halopropyl, halobutyl, methoxymethyl,methoxyethyl, halomethoxymethyl, ethoxymethyl, haloethoxymethyl, propoxymethyl, ethylaminocarbonylmethyl, ethylaminocarbonylethyl, dimethoxyethyl, propynylaminocarbonylmethyl, N-phenyl-N-methyl-amino, haloethylaminocarbonylmethyl, haloethylaminocarbonylethyl, tetrahydrofuryl, methylaminocarbonylmethyl, (N,N-dimethylamino)-carbonylmethyl, propylaminocarbonylmethyl, cyclopropylaminocarbonylmethyl, propenylaminocarbonylmethyl, haloethylaminocarbonylcyclopropyl, wherein Z A = hydrogen, halogen, cyano, halomethyl (CF 3); R 4 = hydrogen, ethyl, methoxymethyl, halomethoxymethyl, ethoxymethyl, haloethoxymethyl, propoxymethyl, methylcarbonyl, ethylcarbonyl, propylcarbonyl, cyclopropylcarbonyl, methoxycarbonyl, methoxymethylcarbonyl, aminocarbonyl, ethylaminocarbonylmethyl, ethylaminocarbonylethyl, dimethoxyethyl, propynylaminocarbonylmethyl, haloethylaminocarbonylmethyl, cyanomethylaminocarbonylmethyl, or haloethylaminocarbonylethyl; or R 3 and R 4 together form a substituent selected from the group consisting of: or a salt or solvate thereof, and a pharmaceutically acceptable carrier comprising diethylene glycol monoethyl ether and a polysorbate surfactant for use in the prevention or treatment of parasite infestations in animals, wherein the composition is orally administered via the drinking water. R 1 = halogen, CF 3, OCF 3, CN, n = integer from 0 to 3, preferably 1, 2 or 3, R 2 = C 1 -C 3 -haloalkyl, preferably CF 3 or CF 2 Cl, T = 5- or 6-membered ring, which is optionally substituted by one or more radicals Y, Y = methyl, halomethyl, halogen, CN, NO 2, NH 2 -C=S, or two adjacent radicals Y form together a chain, especially a three or four membered chain; Q = X-NR 3 R 4 or a 5-membered N-heteroaryl ring, which is optionally substituted by one or more radicals; X = CH 2, CH(CH 3), CH, CO, CS, R 3 = hydrogen, methyl, haloethyl, halopropyl, halobutyl, methoxymethyl,methoxyethyl, halomethoxymethyl, ethoxymethyl, haloethoxymethyl, propoxymethyl, ethylaminocarbonylmethyl, ethylaminocarbonylethyl, dimethoxyethyl, propynylaminocarbonylmethyl, N-phenyl-N-methyl-amino, haloethylaminocarbonylmethyl, haloethylaminocarbonylethyl, tetrahydrofuryl, methylaminocarbonylmethyl, (N,N-dimethylamino)-carbonylmethyl, propylaminocarbonylmethyl, cyclopropylaminocarbonylmethyl, propenylaminocarbonylmethyl, haloethylaminocarbonylcyclopropyl, wherein Z A = hydrogen, halogen, cyano, halomethyl (CF 3); R 4 = hydrogen, ethyl, methoxymethyl, halomethoxymethyl, ethoxymethyl, haloethoxymethyl, propoxymethyl, methylcarbonyl, ethylcarbonyl, propylcarbonyl, cyclopropylcarbonyl, methoxycarbonyl, methoxymethylcarbonyl, aminocarbonyl, ethylaminocarbonylmethyl, ethylaminocarbonylethyl, dimethoxyethyl, propynylaminocarbonylmethyl, haloethylaminocarbonylmethyl, cyanomethylaminocarbonylmethyl, or haloethylaminocarbonylethyl; or R 3 and R 4 together form a substituent selected from the group consisting of: or a salt or solvate thereof, and a pharmaceutically acceptable carrier comprising diethylene glycol monoethyl ether and a polysorbate surfactant for use in the prevention or treatment of parasite infestations in animals, wherein the composition is orally administered via the drinking water.