Re-examining crude coal tar treatment for psoriasis

Two separate, double-blind, randomized, half-and-half body comparisons, each involving 20 in-patients with psoriasis, were conducted to compare the effect of different concentrations of crude coal tar in yellow soft paraffin. The therapeutic effect of 1% crude coal tar used twice daily for 10 days was significantly less than that achieved with an incremental regimen starting at 5% and increasing by 5% every second day to a maximum of 25%. No such difference was seen when a steady concentration of 5% was compared with the same incremental regimen. We conclude that there appears to be no benefit from exceeding a concentration of 5% crude coal tar in yellow soft paraffin in the treatment of patients with psoriasis and that the plateau in the dose-response curve for the action of crude coal tar in psoriasis begins at a point between 1 and 5%.