D2.251 - Allergic Contact Dermatitis to Clonidine Transdermal Patch: Insights From a Rare Case With Prolonged Cutaneous Exposure

Background:Transdermal therapeutic systems (TTS) provide controlled drug delivery and improvetreatment adherence, particularly in chronic conditions such as hypertension. Clonidine TTShas been widely used since its approval, generally showing good tolerability; however, localcutaneous reactions, including allergic contact dermatitis (ACD), are a recognised adverseeffect. While most reactions occur early, delayed sensitisation after prolonged exposure israre and may be underdiagnosed.Case Presentation:We report a 76-year-old woman with hypertension treated with clonidine TTS in addition toramipril and atenolol. After approximately 94 weeks of uneventful therapy, she developedpersistent, pruritic erythematous–desquamative plaques at the application sites, appearingabout 72 hours after patch placement. Clinical features and timing suggested delayed-typehypersensitivity.Methods and Findings:Patch testing was performed using SIDAPA baseline allergen series together with clonidineTTS and the adhesive polyurethane cover routinely applied by the patient. The baselineSIDAPA series and adhesive cover yielded negative results, whereas clonidine TTS eliciteda strong positive reaction with erythema, oedema, vesiculation and blistering, confirmingACD to clonidine. Therapy was discontinued and replaced with an alternative oralantihypertensive agent, with clinical resolution.Conclusions:This case highlights a rare but clinically relevant scenario of late-onset ACD after long-term,previously well-tolerated clonidine TTS. Delayed sensitisation may occur even afterextended exposure and should be considered in patients presenting with persistent localdermatitis at patch sites. Targeted patch testing with the specific drug formulation isessential to confirm diagnosis and differentiate reactions due to active drug from adhesivecomponents. Given the risk of delayed systemic reactions and the availability of safertherapeutic alternatives, oral challenge was not performed. Clinicians should remain awareof this possibility to ensure timely diagnosis and appropriate management.