PROTECTION AGAINST DIHEMATOPORPHYRIN ETHER PHOTOSENSITIVITY

Abstract Amelioration of dihematoporphyrin ether (DHE) induced skin photosensitivity by medications either suspected or known to influence porphyrin metabolism or inflammatory response was evaluated in 357 female athymic NCR-nude mice (308 study animals, 49 controls) in 56 separate study groups. Seventy-two hours after injection with 25 mg/kg of DHE, the study animals'abdomens were irradiated with 4.125-4.25 J/cm² of visible light. Controls were irradiated after receiving either medication, solubilizing agent, or no injection. The abdominal surface burns were examined daily and graded as extensive, partial, or no burn. Statistical comparison was made between irradiated mice injected with DHE only and irradiated mice injected with DHE and medication. Injection of medications which influenced metabolism (hydroxychloroquine, hydrochlorothiazide) produced fewer extensive ( P < 0.01) but greater frequencies of partial burns than DHE controls. Medications which block histamine effect (cimetidine and/or hydroxyzine) resulted in fewer extensive ( P < 0.03) and roughly equal frequencies of partial burns compared with DHE controls. Steroids (dexamethasone, methylpred-nisolone, triamcinolone) which interfere with inflammatory response resulted in similar extensive and partial burn levels. Control animals receiving only medication, solubilizing agent, or no injection had no photosensitivity and consequently showed no burns. The results from this study suggest that inhibition of histamine effect and, to a lesser extent, increased activity of porphyrin catabolic pathways may decrease skin photosensitivity associated with DHE administration.