D2.20 - Selective Fixed Drug Eruption from Etoricoxib with Safe Celecoxib Use: Role of Patch Testing

Etoricoxib is a widely used non-steroidal anti-inflammatory drug (NSAID) and a selective cyclooxygenase-2 (COX-2) inhibitor. It has been implicated in various cutaneous reactions and has been rarely reported as a cause of fixed drug eruption (FDE). We present a new case of etoricoxib-induced FDE confirmed by patch testing.

We report the case of a 40-year-old woman with no relevant allergic history, a past diagnosis of breast cancer in remission under oncological follow-up, and ankylosing spondylitis, treated with tamoxifen and omeprazole.

The patient was evaluated for recurrent erythematous–violaceous plaques with vesicular components, located on the left elbow, lower limbs, and gluteal region, associated with pruritus and pain. Episodes occurred monthly over six months, resolved with corticosteroids, and left residual hyperpigmentation.  Initially, the patient associated the episodes with menstruation due to concomitant use of hormonal contraceptives and on-demand analgesics. The most recent episode followed etoricoxib intake within 24 hours. Patch testing with etoricoxib and celecoxib (10% in vaseline) was performed on healthy and previously affected skin.

A skin biopsy revealed interface dermatitis with basal layer damage and necrotic keratinocytes, findings consistent with a drug-induced cutaneous adverse reaction. Direct immunofluorescence was negative for IgG, IgA, IgM, and C3.Drug causality was subsequently confirmed by patch testing. Patch tests performed on healthy skin with etoricoxib and celecoxib (both at 10% in petrolatum) were negative. In contrast, patch testing with etoricoxib at 10% applied to previously affected skin, including the left elbow and gluteal region showed positive reactions (++ at 48 and 96 hours), confirming etoricoxib as the culprit drug. Celecoxib, a pharmacologically related selective COX-2 inhibitor but structurally distinct as a sulfonamide, yielded negative patch test results on both healthy and previously affected skin. Based on these findings, a graded oral drug provocation test with celecoxib was performed and was well tolerated, with no adverse reactions during the challenge or subsequent therapeutic use, confirming a safe alternative treatment.

This case highlights the diagnostic and clinical value of patch testing in fixed drug eruption, enabling accurate identification of the culprit drug and guiding safe therapeutic alternatives.