title: Topical Benzocaine and Methemoglobinemia.
abstract: Methemoglobinemia can cause life-threatening hypoxia associated with cyanosis and dyspnea not responsive to oxygen. We present a case of recurrent methemoglobinemia because of occult use of topical benzocaine to the vulva. A 47-year-old female with medical history of vulvar cancer and HIV undergoing chemoradiation was sent by the oncology clinic to the emergency department for worsening dyspnea, fatigue, hypoxia to 78% on room air, and gradual onset of cyanosis over the past week. A methemoglobin (MetHb) level was 49%. She received methylene blue, and repeat MetHb levels initially decreased but later increased to 56% despite continued treatment. Additional interviews with the patient revealed she was applying vagicaine (20% benzocaine), an over the counter preparation to the vulvar area for analgesia, and she continued application while hospitalized. She received a total of 6 mg/kg methylene blue and underwent vaginal lavage with 60 mL of sterile saline and cleansed with soapy water. Cyanosis, hypoxia, and dyspnea resolved, and the MetHb level decreased to 5.4% on the day of discharge. Benzocaine is a frequent cause of iatrogenic methemoglobinemia. In this case, additional medication inquiries were helpful in making the diagnosis. Many patients do not consider over-the-counter medications to be potentially harmful. Methemoglobinemia from occult topical benzocaine administration to the vulva is an uncommon exposure route. Occult medication use can be a source of methemoglobinemia.
authors.affiliation: 1Division of Clinical Toxicology, Department of Emergency Medicine, VCU Medical Center, Richmond, VA; 2Virginia Poison Center, Richmond, VA; and 3Department of Emergency Medicine, VCU Medical Center, Richmond, VA.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Hieger
authors.forename: Jamiee L
authors.initials: JL
authors.lastname: Afeld
authors.forename: Kirk L
authors.initials: KL
authors.lastname: Cumpston
authors.forename: Brandon K
authors.initials: BK
authors.lastname: Wills
mesh_terms: D000287:Administration, Topical; D000779:Anesthetics, Local / Q000009:adverse effects*; D001566:Benzocaine / Q000009:adverse effects*; D003490:Cyanosis / Q000209:etiology; D004417:Dyspnea / Q000209:etiology; D004791:Enzyme Inhibitors / Q000627:therapeutic use*; D005221:Fatigue / Q000209:etiology; D005260:Female; D015658:HIV Infections / Q000188:drug therapy; D006801:Humans; D000860:Hypoxia / Q000209:etiology; D008706:Methemoglobin / Q000032:analysis; D008708:Methemoglobinemia / Q000139:chemically induced* / Q000150:complications / Q000175:diagnosis / Q000188:drug therapy; D008751:Methylene Blue / Q000627:therapeutic use; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy* / Q000209:etiology; D012008:Recurrence; D014844:Vulva; D014846:Vulvar Neoplasms / Q000150:complications* / Q000628:therapy
chemical_list: D000779:Anesthetics, Local; D004791:Enzyme Inhibitors; D008706:Methemoglobin; D008751:Methylene Blue; D001566:Benzocaine