a method and composition for the prevention , amelioration or control of external parasites on animals and humans utilizing a compound of formula i . or a pharmaceutically acceptable salt thereof , wherein r is halogen , or 7 , so m r 8 , no 2 , cn , c 1 - c 6 haloalkyl or an optionally substituted c 1 - c 6 alkyl group ; n is 0 or an integer of 1 , 2 or 3 ; m is 0 or an integer of 1 or 2 ; r 1 is h , halogen , no 2 , nr 9 r 10 , nr 11 cor 12 , nchnr 9 r 10 or nchor 13 ; r 2 , r 3 , r 4 , r 5 and r 6 are each independently h , halogen or a c 1 - c 4 alkyl , aryl or heteroaryl group each optionally substituted ; r 7 is h or a c 1 - c 6 alkyl , c 2 - c 6 alkenyl , c 2 - c 6 alkynyl , aryl or heteroaryl group each optionally substituted ; r 8 is a c 1 - c 6 alkyl , c 2 - c 6 alkenyl , c 2 - c 6 alkynyl , aryl or heteroaryl group , each optionally substituted ; r 9 and r 10 are each independently h , c 1 - c 4 haloalkyl or a c 1 - c 6 alkyl , c 2 - c 6 alkenyl , c 2 - c 6 alkynyl , aryl or heteroaryl group each optionally substituted or r 9 and r 10 may be taken together with the atom to which they are attached to form a 5 - to 7 - membered ring optionally containing 1 or 2 additional heteroatoms selected from o , n or s ; r 11 is h , cor 12 or an optionally substituted c 1 - c 4 alkyl group ; r 12 is a c 1 - c 6 alkyl , c 2 - c 6 alkenyl , c 2 - c 6 alkynyl , aryl or heteroaryl group each optionally substituted ; and r 13 is h or a c 1 - c 6 alkyl , aryl or heteroaryl group each optionally substituted ; or a stereoisomer or tautomer thereof .