The lesions will blanch, become dry and decrease in size. This regimen may be repeated for up to 4 weeks of treatment. Application is made with a cotton applicator to an area less than 10 cm 2 and using less than 0.5 ml of the preparation. The clinical response resembles that described above for the resin. These agents decrease mitosis and rate of proliferation of epidermal cells by decreasing DNA synthesis.
Coal tar is used primarily in the treatment of chronic psoriasis.
They are contraindicated in acute flare-ups of psoriasis, since their systemic absorption would be increased. Side effects include excessive irritation, hypersensitivity, and photosensitivity. Additionally, exposure to sunlight will increase the risk of cancer as an extension of the pharmacologic effect of the preparation. They may also discolour nails and white or grey hair. Systemic absorption may cause nephrotoxicity, hepatoxicity, or cancer.