Topical gel containing 3% diclofenac in 2.5% hyaluronic acid (HYAL CT1101) is used for the treatment of actinic keratosis. In animal models, diclofenac in hyaluronic acid inhibited angiogenesis and induced neovascular regression in inflammatory tissue, and depleted substance P content in snout tissue. Diclofenac delivered in hyaluronic acid appears to accumulate in the epidermis of human skin in vitro and mice in vivo. Results of clinical trials indicate that topical HYAL CT1101 is effective in the treatment of actinic keratosis. A clinical cure (all lesions fully resolved) was seen in 47% of 108 patients using HYAL CT1101 compared with 19% of patients using placebo after 3 months in 1 randomised, double-blind study. Mild to moderate skin irritation has been reported in up to 72% of patients treated with HYAL CT1101 in clinical studies.