What is the treatment for nitrate toxicity?

• A. Vitamin K
• B. Activated charcoal
• C. Vitamin C
• D. Methylene blue

Answer: (D)

Nitrate (nitrite) toxicity causes methemoglobinemia, where hemoglobin is oxidized to methemoglobin and can no longer carry oxygen, leading to tissue hypoxia. The treatment works by rapidly reducing methemoglobin back to functional hemoglobin. Methylene blue acts as an artificial electron donor in the NADPH-dependent methemoglobin reductase system, converting methemoglobin to normal hemoglobin quickly. It’s given by IV at about 1–2 mg/kg, and can be repeated once after 30–60 minutes if methemoglobinemia persists. Provide supportive care such as supplemental oxygen and fluids while monitoring.

Other options don’t address the oxygen-carrying defect directly: vitamin K is for anticoagulant-related bleeding, not nitrate toxicity; activated charcoal helps with some ingested toxins but won’t reverse methemoglobinemia; vitamin C can reduce methemoglobin slowly but is not the reliable antidote methylene blue provides.