FIELD: pharmacology.SUBSTANCE: invention relates to a compound of formula (I) or a pharmaceutically acceptable salt thereof, in which R1 represents -halo or -CF3； R4 represents -H or -CH3； each of R8 and R9 independently represents -H, -halo, -CH3 or -OCH3, each halo independently represents -F, -Cl, -Br or -I； and m means an integer of 0 or 1； (1) provided that if R4 represents -H, the m means 1； and (2) provided that if R4 represents -H and the carbon atom in the position a of the a-b bond is in (S)-configuration, the methyl group connected to piperazinonyl ring represents a (S)-2-methyl group, a (S)-3-methyl group or a (R)-3-methyl group； (3) provided that if R4 represents -H, the carbon atom in position a of the a-b bond is in (S)-configuration, R8 represents -H and R9 represents -halo, then the methyl group connected to piperazinonyl ring represents a (R)-3-methyl group； (4) provided that if R4 represents -H, the carbon atom in position a of the a-b bond is in (S) configuration, R8 represents -F and R9 represents -F, then the methyl group connected to piperazinonyl ring represents a (S)-2-methyl group or a (S)-3-methyl group； and (5) provided that if R4 represents -CH3, each of the carbon atoms in positions a and c and the a-b bond and the c-d bond is in (S) configuration,R8 represents -H, R9 represents -halo, and m means 1, the methyl group connected to piperazinonyl ring is a (S)-3-methyl group or a (R)-3-methyl group. Invention also relates to a compound of formula (II) or a pharmaceutically acceptable salt thereof, a specific compound of formula (Ia) or a pharmaceutically acceptable salt thereof and / or a co-crystal of fumaric acid. Invention also relates to specific compounds of formula (Ib) or a pharmaceutically acceptable salt thereof. The compounds as per invention are intended to inhibit the function of TRPV1 in a cell and to treat pain, pain associated with osteoarthritis, osteoarthritis, urinary incontinence (UI), ulcer, inflammatory bowel disease (
