Photosensitizing drugs may lower the narrow-band ultraviolet B (TL-01) minimal erythema dose

S ir, Does it matter if patients attending for narrow‐band (TL‐01, 311–313 nm) ultraviolet (UV) B phototherapy are on known phototoxic systemic therapy? Many patients attending for treatment of psoriasis, atopic dermatitis and other conditions are taking potentially photoactive medication including non‐steroidal anti‐inflammatory drugs (NSAIDs), thiazide diuretics, quinine, phenothiazines and fluoroquinolones. Such agents are known to be photoactive within the UVA wavebands, with extension into the UVB region in some. 1–4 Stern et al. have examined the use of these drugs during PUVA, 5 and found a slightly increased risk of burning, resulting in the need for discontinuation of PUVA therapy, particularly in older patients. No work which examines the effect of photoactive medication during UVB has been published. A prospective study was established to record current medication and minimal erythema dose (MED) in all patients starting UVB (TL‐01). The MED was measured by irradiating eight 1·5 × 1·5 cm squares on the patient’s back with a series of UVB TL‐01 doses (25, 50, 70, 100, 140, 200, 280 and 390 mJ/cm2 in skin types I and II, and 50–550 mJ/cm2 in skin types III and IV) using a unit consisting of eight TL‐01 tubes, the output of which was measured monthly with an IL1400A radiometer/photometer. Calibration is traceable to the National Physical Laboratory. The MED was defined as the dose required to cause just perceptible erythema at 24 h. Patients with known abnormal photosensitivity were excluded.