A SIMPLE METHOD TO PREDICT WHETHER TOPICAL AGENTS WILL INTERFERE WITHPHOTOTHERAPY

The objective of this study was to assess the potential interference o f topical agents commonly used in psoriasis with concurrent photothera py. Twenty-one commercially available topical agents were tested. To c reate solutions from the creams, lotions, and ointments, extractions w ere made using three different solvents (95 percent ethanol, hexanes, and 1,4-dioxane) and their absorbance from 260 to 400 mn was measured. The absorbance value of the solutions at 310 mn 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 agent s for potential interference with psoralen/ultraviolet A (PUVA) therap y. Salicylic acid-containing preparations had substantial absorption i n 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. Calcipotri ene (Dovonex(R)) showed a maximal absorbance in the ultraviolet C (UVC ; 200 to 280 nm) and UVB range. Tretinoin (Retin-A(R)) had substantial absorbance in the UVA range. Anthralin (Drithocreme(R)) revealed maxi mal absorbance within the UVC and UVB ranges. Topical steroid preparat ions and ammonium lactate (LacHydrin(R)) had low absorbance in both UV B and UVA ranges. In conclusion, salicylic acid-containing preparation s, tar-based products, calcipotriene, anthralin, and most tretinoin pr eparations should be removed before and/or applied after phototherapy.