Tacrolimus ointment neither blocks ultraviolet B nor affects expression of thymine dimers and p53 in human skin.

Background: There is a lack of data with regard to the interaction between ultraviolet (UV) radiation and topical calcineurin inhibitors.

Objective: We aimed to investigate (1) the UV transmission through tacrolimus ointment and (2) the impact of topical exposure to tacrolimus on the protein expression of thymine dimers (TD) and p53 in human skin.

Methods: Spectrophotometric measurements (290-400 nm) of tacrolimus ointment and the vehicle were performed. Eight subjects were treated with tacrolimus ointment and the vehicle thrice daily over a 3-day period on the back. Pre-treated sites and one control site were exposed to two minimal erythema doses UVB. Skin biopsies were taken 1h and 24h after irradiation. Immunohistochemical procedures were used for the detection of TD and p53.

Results: Mean UV transmission was over 94% and did not significantly differ between tacrolimus ointment and the vehicle. Immunohistological examinations of TD and p53 expression did not demonstrate significant differences between irradiated sites, irradiated plus vehicle treated sites, and irradiated plus tacrolimus treated sites both 1h and 24h post-irradiation.

Conclusions: The present data suggest that tacrolimus ointment hardly has UV blocking capacities and does not significantly interfere with development and/or removal of local DNA damage in human skin.