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Extensive investigations failed to identify either an endogenous or ingested oxidant source until nursing staff observed the patient applying a topical dapsone\u2013adapalene cream brought from home. Discontinuation of the cream resulted in complete and sustained clinical resolution. This case highlights persistent methaemoglobinaemia due to ongoing topical oxidant exposure and underscores the importance of considering inadequate decontamination in refractory cases.<\/jats:p>","DOI":"10.1136\/bcr-2025-271194","type":"journal-article","created":{"date-parts":[[2026,2,10]],"date-time":"2026-02-10T15:24:35Z","timestamp":1770737075000},"page":"e271194","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":1,"title":["Persistent methaemoglobinaemia due to unsupervised use of topical dapsone\u2013adapalene"],"prefix":"10.1136","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0913-852X","authenticated-orcid":false,"given":"Shrirang","family":"Joshi","sequence":"first","affiliation":[{"name":"Emergency Medicine, All India Institute of Medical Sciences New Delhi, New Delhi, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Prajwal","family":"Rao","sequence":"additional","affiliation":[{"name":"Emergency Medicine, All India Institute of Medical Sciences New Delhi, New Delhi, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Prasad","family":"Achari","sequence":"additional","affiliation":[{"name":"Emergency Medicine, All India Institute of Medical Sciences New Delhi, New Delhi, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Prakash","family":"Mishra","sequence":"additional","affiliation":[{"name":"Emergency Medicine, All India Institute of Medical Sciences New Delhi, New Delhi, India"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2026,2,10]]},"reference":[{"key":"2026021023551509000_19.2.e271194.1","unstructured":"Ludlow JT , Wilkerson RG , Nappe TM . 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