A simple method to predict whether topical agents will interfere with phototherapy.

The objective of this study was to assess the potential interference of topical agents commonly used in psoriasis with concurrent phototherapy. Twenty-one commercially available topical agents were tested. To create solutions from the creams, lotions, and ointments, extractions were made using three different solvents (95 percent ethanol, hexanes, and 1,4-dioxane) and their absorbance from 260 to 400 nm was measured. The absorbance value of the solutions at 310 nm was used to rank the various agents in terms of potential interference with ultraviolet B (UVB) phototherapy. The absorbance at 360 nm was used to rank the agents for potential interference with psoralen/ultraviolet A (PUVA) therapy. Salicylic acid-containing preparations had substantial absorption in the UVB (280 to 320 nm) range. The tar-based products had impressive absorbance in both the UVA (320 to 400 nm) and UVB ranges. Calcipotriene (Dovonex) showed a maximal absorbance in the ultraviolet C (UVC; 200 to 280 nm) and UVB range. Tretinoin (Retin-A) had substantial absorbance in the UVA range. Anthralin (Drithocreme) revealed maximal absorbance within the UVC and UVB ranges. Topical steroid preparations and ammonium lactate (Lac-Hydrin) had low absorbance in both UVB and UVA ranges. In conclusion, salicylic acid-containing preparations, tar-based products, calcipotriene, anthralin, and most tretinoin preparations should be removed before and/or applied after phototherapy.