Studies on the contact sensitizing activity of dithranol (anthralin) and 10-butyryl dithranol (butantrone)

The contact sensitizing activity of dithranol and butantrone (10-butyryl dithranol) was studied in 3 animal models: the guinea pig maximization test (GPMT), the closed patch test (CPT), and the mouse ear swelling test (MEST) in 2 different mouse strains. In the GPMT, both dithranol and, to a greater extent, butantrone showed sensitizing potential. Because butantrone was less irritant, the concentrations used were 10x higher than those of dithranol. In the CPT, only butantrone was slightly positive. In the MEST, with both CF-1 and Balb/c mice, dithranol caused less swelling of the test ear after challenge than butantrone. According to the evaluation criteria of the MEST, only butantrone caused sensitization in 50% of the CF-1 mice and in 40% of the Balb/c mice. Thus, the GPMT was the only test which indicated the minor contact sensitizing potential of dithranol. On the other hand, the 10-butyryl analogue of dithranol showed undoubtedly stronger contact sensitizing potential than the parent compound in all tests. Therefore, as compared to dithranol, an increased risk of sensitization should be considered.