Diclofenac Sodium is a non-steroidal anti-inflammatory drug (NSAID). It can be used to treat: Inflammation of the bones and joints such as rheumatoid arthritis, osteoarthritis, acute gout and ankylosing spondylitis. Back pain. Sprains, strains, sport injuries, dislocations and fractures. Conditions affecting the tendons such as tendonitis. Mild pain.