Background Many excipients have been reported to induce drug hypersensitivity (e.g. colouring additives, preservatives). Colloidal silica has never been reported to induce drug hypersensitivity reactions. Case report We report herein a 40-year-old patient who developed a skin eruption 2 days after Voltarene^® (diclofenac) intake, confirmed by a positive patch test. Investigation of cross reactivity, assessed by patch testing to other non steroidal anti-inflammatory drugs, have showed a positive reaction only to piroxicam (Piroxen^®), ketoprofen (Oki^®) and indometacin (Indocid^®)

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