The present invention provides a compound of formula (1) or a pharmaceutically acceptable salt thereof: wherein R1 represents optionally substituted C1-4 alkyl； X represents &mdash；(CR10R11)n&mdash； in which n represents 1 or 2； R2, R3 and R4 independently represent H, F or Me； and R5； R6； R7； R8 and R9 independently represent hydrogen, halogen, or cyano； or optionally substituted C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl or C3-6 cycloalkyl, such that at least one of R5 and R9 represents a group other than hydrogen. The compounds or salts are thought to modulate P2X7 receptor function and to be capable of antagonizing the effects of ATP at the P2X7 receptor. The invention also provides the use of the compound or salt in the treatment or prevention of inflammatory pain, neuropathic pain, visceral pain, rheumatoid arthritis or osteoarthritis.
