Local Anesthetic-Induced Methemoglobinemia During Pregnancy: A Case Report and Evaluation of Treatment Options.

BACKGROUND: Methemoglobinemia is a well-recognized adverse drug reaction related to the use of certain local anesthetic agents. The mainstay of treatment for methemoglobinemia is i.v. methylene blue, along with provision of supplemental oxygen; however, methylene blue is listed as a category X teratogen. This poses an issue should methemoglobinemia develop during pregnancy.

CASE REPORT: A 35-year-old, 20-week and 5-day gravid female was transferred from an outpatient oral surgeon's office for hypoxia. She was undergoing extraction of 28 teeth and was administered an unknown, but "large" quantity of prilocaine during the procedure. Given this exposure, the concern was for methemoglobinemia. This was confirmed with co-oximetry, which showed 34.7% methemoglobin. The initial treatment plan was methylene blue; however, this drug is a category X teratogen. Thus, an interdisciplinary team deliberated and decided on treatment with high-dose ascorbic acid and transfusion of a single unit of packed red blood cells. The patient was managed with noninvasive ventilation strategies and a total of 8 g ascorbic acid. She was discharged on hospital day 3 with no obstetric issues noted. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Intravenous ascorbic acid appears to be a potential alternative to methylene blue in this patient population. The data surrounding teratogenicity of methylene blue are mostly related to intra-amniotic or intra-uterine administration. In life-threatening cases of methemoglobinemia during pregnancy, the benefits of i.v. methylene blue may outweigh the risks.