What is the appropriate management of mothball (naphthalene) poisoning?

Management of Mothball (Naphthalene) Poisoning

Immediately provide aggressive supportive care with high-flow oxygen, monitor for hemolysis and methemoglobinemia, and administer methylene blue (1-2 mg/kg IV over 5 minutes) for methemoglobin levels >20-30%, unless the patient has G6PD deficiency—in which case use red blood cell exchange transfusion or ascorbic acid instead.

Initial Assessment and Stabilization

Upon presentation, rapidly assess for the classic toxidrome of naphthalene poisoning:

• Cyanosis with low oxygen saturation (often 50-85% on pulse oximetry despite adequate ventilation)
• Chocolate-colored blood on blood draw
• Dark brown or cola-colored urine (hemoglobinuria)
• Scleral icterus and jaundice (from acute hemolysis)
• Abdominal pain and vomiting

Obtain immediate arterial blood gas to measure methemoglobin levels and assess metabolic status. The blood will appear chocolate-brown and will not change color with oxygen exposure 1, 2.

Laboratory Evaluation

Order the following stat labs:

• Methemoglobin level (arterial blood gas with co-oximetry)
• Complete blood count with peripheral smear (look for Heinz bodies, bite cells, hemolysis)
• Reticulocyte count
• Lactate dehydrogenase, haptoglobin, indirect bilirubin (hemolysis markers)
• Renal function (BUN, creatinine—naphthalene causes acute tubular necrosis)
• Urinalysis (hemoglobinuria without RBCs on microscopy)
• G6PD enzyme assay (critical before methylene blue administration)

Treatment Algorithm

For Methemoglobin >20-30% WITH Normal G6PD:

1. Methylene blue 1-2 mg/kg IV over 5 minutes 2, 3
2. Repeat dose in 30-60 minutes if no improvement
3. Continue high-flow 100% oxygen
4. Add ascorbic acid 1-2 g IV and N-acetylcysteine as adjunctive therapy 4, 2

For Methemoglobin >20-30% WITH G6PD Deficiency:

Methylene blue is absolutely contraindicated as it will worsen hemolysis 5, 3. Instead:

1. Red blood cell exchange transfusion (most effective, rapidly normalizes oxygen saturation) 5
2. High-flow 100% oxygen (hyperbaric oxygen if available)
3. Ascorbic acid 1-2 g IV every 4-6 hours 1, 5
4. N-acetylcysteine 5, 4
5. Consider plasmapheresis if RBC exchange unavailable 4

For Severe Hemolysis:

• Packed red blood cell transfusions as needed to maintain hemoglobin >7 g/dL 1, 2
• Aggressive IV hydration to prevent acute tubular necrosis from hemoglobinuria
• Folic acid supplementation to support erythropoiesis 1
• Monitor urine output closely; may require hemodialysis for acute renal failure 4

Critical Pitfalls to Avoid

1. Do NOT give methylene blue without confirming G6PD status first—this is the most dangerous error and will cause catastrophic hemolysis in G6PD-deficient patients 5, 3

2. Do NOT rely on pulse oximetry alone—methemoglobin causes falsely low readings; always obtain co-oximetry 1

3. Do NOT delay treatment waiting for confirmatory testing—if clinical suspicion is high (chocolate blood, cyanosis, hemoglobinuria), treat empirically while awaiting labs 2

4. Do NOT discharge early—hemolysis can continue for 48-72 hours after exposure; observe until hemolysis markers stabilize 3

Supportive Care Essentials

• Continuous cardiac monitoring (arrhythmias from severe anemia/hypoxia)
• Serial methemoglobin levels every 2-4 hours until <5%
• Daily CBC and hemolysis markers for at least 3 days
• Maintain urine output >1 mL/kg/hr with IV fluids to prevent renal failure
• Consider psychiatric evaluation if intentional ingestion 4

Expected Clinical Course

With appropriate treatment, methemoglobin levels normalize within hours of methylene blue or RBC exchange 5, 2. Hemolysis typically resolves over 5-7 days with supportive care 1. Full recovery is expected in most cases, though severe cases may require 2-3 weeks of hospitalization 4.

The toxicity is markedly worse in G6PD-deficient patients and carries higher morbidity and mortality 3. Always test for G6PD deficiency during follow-up if not done acutely 1, 5.