Arachidonic acid and prostaglandin levels in dithranol erythema: time course study.

Arachidonic acid and prostaglandins were measured in uninvolved psoriatic skin before and after treatment for up to 24 h with dithranol. Prior to treatment, skin exudate contained 2744 ng ml-1 arachidonic acid and 26.4 ng ml-1 PGE2. After treatment with dithranol, the arachidonic acid concentration increased to a maximum of 5556 ng ml-1 at 48 h whilst PGE2 increased to 93.4 ng ml-1 at 12 h and then declined. The erythemal response was apparent at 6-12 h and maximal at 72 h. These results suggest that PGE2 mediates the early development of dithranol erythema.