Persistence of patch test reactions to clioquinol (Vioform) and cross-sensitization.

Ten patients with positive patch test reactions to clioquinol were retested in 1979 after an average interval of 6 years. On subsequent testing we also examined test reactions to other quinoline derivatives (including antimalarial drugs) and potassium iodide. All patients showed a positive reaction to clioquinol at retesting. Many cross-reactions of hydroxyquinolines included reactions to quinoline-based antimalarial drugs, and a few allergic reactions to potassium iodide. The consequences of these findings are discussed.