Oxicam-induced photosensitivity. Patch and photopatch testing studies with tenoxicam and piroxicam photoproducts in normal subjects and in piroxicam-droxicam photosensitive patients.

BACKGROUND: The mechanism of piroxicam-induced photosensitivity is unknown. It was first attributed to metabolites of the drug produced in vivo but further photochemical studies disclosed that piroxicam was not stable to light, forming at least two photoproducts. Photosensitivity reactions to droxicam and tenoxicam have been not reported.

OBJECTIVE: The aim of this study was to determine whether piroxicam photoproducts contribute to the light reactions induced by this drug, to describe a case of droxicam-induced photosensitivity and to study the in vivo photosensitizing potential of tenoxicam.

METHODS: Patch and photopatch tests with two major photoproducts of piroxicam, with different preparations of UVA-preirradiated piroxicam, and with low and high concentrations of tenoxicam were performed in normal volunteers and in piroxicam-photosensitive patients. Phototesting studies were also performed before and after the oral administration of tenoxicam in both groups of subjects.

RESULTS: Positive patch test responses were obtained in piroxicam-photosensitive patients only with the preirradiated piroxicam preparations. Phototesting studies with tenoxicam were normal in both groups.

CONCLUSION: Minor or intermediate piroxicam photoproducts are more likely to be responsible for the photosensitivity reactions induced by this drug.