Cross-reactivity between sensitivity to thimerosal and photosensitivity to piroxicam in guinea pigs.

Piroxicam (PXM) is a nonsteroidal anti-inflammatory drug which may induce a photosensitive eruption shortly after administration. We examined whether animals sensitized to thimerosal developed a photosensitivity to PXM. Male Hartley strain guinea pigs were sensitized to thimerosal, thiosalicylate and PXM separately. The open patch test was used to evaluate sensitization to each drug and cross-reactions between the drugs. Animals sensitized to thimerosal exhibited positive patch test reactions to thiosalicylate and positive photopatch test reactions to PXM. Both those sensitized to thiosalicylate and to PXM showed positive patch test reactions to PXM. This study demonstrated that thimerosal induces cross-sensitivity to PXM in vivo and that the common active component among these compounds may be thiosalicylate.