Topical diclofenac sodium (pennsaid) is a non-steroidal-anti- inflammatory drug that is used to manage the recurrent pain and symptoms of osteoarthritis of the knee. Pennsaid is applied topically, absorbed cutaneously and concentrates locally at the site of application. Tugwell et al. [54] has shown that pennsaid is as efficacious as oral diclofenac as a mode of pain relief without systemic effects. The most common side effect induced by pennsaid is the development of dry skin at the site of application. This is caused by dimethyl sulfoxide which is the vehicle used in the pennsaid formulation. Dimethyl sulfoxide dissolves the natural oils in the skin causing dryness
