Photoallergy to systemic quinidine in the mouse

Using the mouse, photoallergy to the antiarrhythmic agent quinidine could be induced following systemic administration. After pretreatment with cyclophosphamide 150 mg/kg, groups of 5-10 mice were injected i.p. with quinidine chloride 100 mg/kg on 2 consecutive days, followed by exposure of shaved abdominal skin to UVB 0.1 J/cm2 and UVA 5.0 J/cm2. Five days later challenge was performed on the left ear and on the tail, using the same dose of quinidine and UVA 5.0 J/cm2. The reaction was elevated 24 h later by measuring the increase in ear thickness as well as the wet weight increase of ear and tail. Significant 24 h reactions could be measured using all three evaluation systems. Control animals treated according to the protocol, but not UV-exposed during induction, were negative, thus excluding a phototoxic reaction. The histology of the left ear at challenge showed a round cell infiltrate preferentially of the exposed outer face of the ear consistent with an immunologic reaction. The time course of the reaction showed a maximum at 24 h. Photosensitization to quinidine could be achieved with UVA alone during the induction phase. Quinidine photoallergy can be induced in the mouse after systemic administration, and the reaction measured both at ear and tail. These findings support the assumption that clinical photoreactions to quinidine may have an immunological basis.