Systemic quinine photosensitivity with photoepicutaneous cross-reactivity to quinidine

A 75-year-old man developed an eczematous eruption on the face and dorsal aspects of the hands one July after 3 weeks' treatment with quinine, 0.25 g nightly, for nocturnal leg cramps. The photoreaction cleared within a week of quinine being stopped. UVA and UVB erythema threshold determinations, after the acute episode had subsided, were normal. A photopatch test was positive for irradiated quinine down to a concentration of 0.01% and for unirradiated quinine to 0.5%. The test with the isomer quinidine was positive only when irradiated, down to a concentration of 0.01%. Preirradiated samples of quinine and quinidine were negative. Whereas in contact allergy quinine and quinidine usually do not cross-react, after systemic photosensitization, the 2 isomers probably form a common photoproduct, accounting for the cross-reactivity.