Citalopram‐induced DRESS confirmed by patch testing

We report a 46-year-old man who developed a Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) from citalopram. SSRI-associated cutaneous adverse drug reactions are rare1 despite their widespread use2 and very few cases of DRESS have been reported. A 46-year-old man developed an acute widespread rash and facial oedema 4 weeks after starting citalopram for anxiety (Figure 1). He was on no other medication, had no known allergies and had never previously taken an selective serotonin reuptake inhibitors (SSRIs). Clinical features, blood results and skin biopsy were consistent with DRESS; he had deranged liver function tests and serum eosinophilia. Citalopram was stopped and his rash resolved over several weeks with oral and topical corticosteroids. Six months later, he was patch-tested to the extended British baseline series and citalopram (crushed tablet in 50% petrolatum). Allergens were obtained from Chemotechnique (Vellinge, Sweden) and applied on Smart Practice allergEAZE chambers (Arizona, USA). Readings were performed on day 2 (D2) and day 4 (D4) according to European Society of Contact Dermatitis criteria. Multiple allergies were identified (Table 1) with positive reactions to citalopram (D2++ and D4+++) (Figure 2). To investigate cross-reactivity, he was subsequently patch tested to fluoxetine, paroxetine and sertraline (in 50% pet.); only paroxetine showed a positive reaction (D2− and D4+). One of the authors (SW) volunteered to be patch tested to citalopram and paroxetine to act as a normal control; the test was negative with no irritancy. While testing of a single control person is a limitation of this report (particularly as the citalopram test concentration was high at 50%), the strongly positive (D2++ and D4+++) reactions in the patient and complete lack of irritancy in the control support our conclusion that the patient's patch test response was a true positive reaction. We did not consider it ethical to test 'control' patients with such a commonly used drug due to the potential risk of active sensitisation. SSRIs are extensively and increasingly used for depression and other mental health problems; 45 000 000 UK prescriptions were issued in the last financial year.2 Despite their widespread use, SSRI-associated cutaneous adverse drug reactions (CADRs) appear to be rare. From 1998 to 2022, the Medicines and Healthcare products Regulatory Agency recorded 16 586 adverse reactions to citalopram, of which only 1077 (6.49%) were cutaneous.1 Rashes ranging from maculopapular eruptions to Toxic Epidermal Necrolysis/Steven Johnson Syndrome have been attributed to SSRIs; there have been isolated reports of DRESS associated with citalopram,3 fluoxetine4 and escitalopram5, 6 (S-enantiomer of citalopram) in the past. The sensitivity and specificity of patch tests for diagnosing delayed CADR varies according to the drug and rash. Positive patch tests have been reported to sertraline7 (1%, 5% and 10% aq., eth. and pet.) and paroxetine8 (1% and 3% in pet.) following maculopapular exanthems. Here, we highlight a diagnostic role for patch tests with an extemporaneous preparation in SSRI-induced DRESS. Despite their diverse chemical structures, cross-reactivity has been reported among SSRIs.9 Our case supports the importance of patch tests in identifying potential cross-reactivity and in finding a safer alternative should further SSRI treatment be necessary. We have obtained permission from the patient to publish his information, and written consent to publish his images. Alpa Kanji: Conceptualization; investigation; writing – original draft; writing – review and editing; methodology; visualization; formal analysis; data curation; resources. Sharan Kapadia: Writing – review and editing; data curation; investigation. Sarah Wakelin: Conceptualization; investigation; methodology; writing – review and editing; supervision. The authors have no conflicts of interest.