To be effective, the incident radiation must be absorbed by a target or chromophore in the skin—which in phototherapy is endogenous and in photochemotherapy must be administered exogenously (Table 65 –6). Patients treated with these modalities should be monitored for concomitant use of other potential photosensitizing medications before initiation of therapy. Such drugs include phenothiazines, thiazides, sulfonamides, nonsteroidal anti-inflammatory agents, sulfonylureas, tetracyclines, and benzodiazepines.