The present invention provides a compound of formula (I) or a pharmaceutically acceptable salt thereof: wherein A is hydrogen, C1-4alkyl, C3-6cycloalkyl, C1-3alkoxy, C1-3alkoxy C1-4alkyl, C1-2fluoroalkyl, halogen, NR6R7, optionally substituted heteroaryl (Het), or optionally substituted phenyl, and R1, R2, R3, R4, R5, R6 and R7 are as defined in the description. 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 prophylaxis of, for example, inflammatory pain, neuropathic pain, visceral pain, rheumatoid arthritis or osteoarthritis or neurodegenerative disorders.