A 36-year-old man, with no medical history of interest, attended the Emergency Department, presenting with paraesthesia in both upper limbs, accompanied by drowsiness. Two hours before admission, he referred the application of 270 g (9 bottles of 30 g) of EMLA® anaesthetic cream (lidocaine 2.5%, prilocaine 2.5%) for laser depilation on the back, upper and lower limbs. The patient was conscious and oriented, sleepy and cyanosed. Blood pressure was 144/83 mmHg, heart rate 82 bpm and a baseline SaO2 of 91%, so oxygen therapy was started until SaO2 94% was reached. The rest of the examination was normal. Complementary tests (chest X-ray and electrocardiogram) showed no significant pathological alterations.
The admission blood test (4 hours after application of EMLA®, see Table 1) showed a methaemoglobin level of 10.1%, and he was diagnosed with severe methaemoglobinaemia secondary to topical administration of EMLA® (lidocaine 2.5%, prilocaine 2.5%). Administration of 100 mg methylene blue was started intravenously within 10 minutes. One hour after administration of the antidote, his methaemoglobin level remained elevated (2.7%), and he also presented alkalosis, so he was assessed by the Intensive Care Unit. After transfer to this unit, he continued high-flow mask oxygen therapy, improving the cutaneous-mucosal discolouration and recovering SaO2 to 96%. Twenty-four hours after the application of EMLA®, the patient remained haemodynamically stable and the methaemoglobin level dropped to 0.2%, so it was decided to transfer him to the Internal Medicine Department, where, given his favourable evolution, it was decided to discharge him three days after his admission.