A proprietary combination of diclofenac sodium (an non-steroidal anti-inflammatory drug) and misoprostol (a prostaglandin analogue), used for the treatment of rheumatoid arthritis and osteoarthritis; the misoprostol is added to prevent the gastric bleeding and ulceration that may result from the use of diclofenac alone. Arthrotec is available, on prescription only, as tablets of two strengths of diclofenac (Arthrotec 50 and Arthrotec 75).