A compound of the formula
wherein
R1 is C1-3 alkyl optionally substituted with one or more fluorines;
R2 is C1-6 alkyl, cycloalkyl or NR4R5;
R3 is a pyrazole, imidazole or isoxazole group of partial formula (A), (B) or (C)
NR4R5 is a nitrogen-containing heterocyclic ring;
R6 is C1-3 alkyl; and
R7 and R8, which are the same or different, each represents C1-3 alkyl, halogen, CF3 or CN;
or a pharmaceutically-acceptable salt thereof.