Abstract A 46-year-old man was referred for investigation of an acute widespread rash and fever that started 4 weeks after commencing citalopram. Clinical and histological features were consistent with drug reaction with eosinophilia and systemic reaction (DRESS). He was not on any other medication, had no known allergies and had not previously taken a selective serotonin reuptake inhibitor (SSRI). Six months after resolution, he was patch tested to the extended British Baseline Series and citalopram (crushed tablet in 50% petrolatum). Readings on days 2 (D2) and 4 (D4) were positive for citalopram (D2 ++ and D4 +++). To investigate possible crossreactivity, he was subsequently patch tested to fluoxetine, paroxetine and sertraline (crushed tablets in 50% petrolatum), which showed a positive reaction to paroxetine [D2 (–) and D4 (+)]. Patch tests to citalopram and paroxetine were negative with no irritancy in a normal volunteer. 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. Despite such widespread use, 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 (6.5%) were cutaneous. Various rashes have been reported to arise from SSRI treatment, ranging from maculopapular eruptions to toxic epidermolysis necrolysis/Stevens–Johnson syndrome. There have been isolated reports of DRESS from fluoxetine, sertraline and escitalopram (the S-enantiomer of citalopram). To our knowledge, this is the first reported case of citalopram-induced DRESS. The sensitivity and specificity of patch tests in the diagnosis of delayed CADR varies according to the drug and rash. We have found case reports of positive patch tests to sertraline and paroxetine following maculopapular exanthems. Our findings highlight a diagnostic role for patch tests with an extemporaneous preparation in SSRI-induced DRESS. SSRIs have diverse chemical structures, and we speculate that patch tests may be of benefit in identifying a safer alternative should further SSRI treatment be needed.
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