Sulpha (Sulfonamide) Poisoning - Management

1. Toxic Syndromes in Sulpha Poisoning

A. Urinary Tract Toxicity (Crystalluria)

• Sodium bicarbonate to alkalinize the urine (target urine pH >7)
• Aggressive IV/oral hydration to increase urine flow
• Monitor urine output and renal function
• Reduce/stop the offending drug if crystalluria is severe

B. Methemoglobinemia

Key diagnostic clue: Cyanosis that does NOT improve with supplemental oxygen. Blood is classically "chocolate brown." Pulse oximetry is unreliable - CO-oximetry is required for accurate diagnosis.

1. Assess airway, breathing, circulation - exclude other causes of cyanosis
2. Establish IV access
3. Administer 100% supplemental oxygen
4. Attach cardiac monitor and pulse oximeter (or preferably co-oximeter)
5. Obtain ECG as indicated
6. Decontaminate as needed (activated charcoal if oral ingestion is recent and stable)
7. Methylene blue - indicated if:
   • Symptomatic at any level, OR
   • MetHb >25% even if asymptomatic
   • Dose: 1 mg/kg IV (0.1 mL/kg of 1% solution, ~7 mL in an adult) over 5 minutes (slow IV to avoid pain)
   • Clinical improvement expected within 20 minutes
   • Repeat dose if cyanosis persists >1 hour
   • Mechanism: Methylene blue is reduced by NADPH-MetHb reductase (via hexose monophosphate shunt) to leucomethylene blue, which reduces Fe³+ back to Fe²+

• G6PD deficiency: NADPH production is impaired, so methylene blue cannot work; supportive care + consider exchange transfusion or packed RBC transfusion if unstable
• Sulfhemoglobinemia: Clinically indistinguishable from methemoglobinemia but NOT responsive to methylene blue (sulfur atom irreversibly binds porphyrin ring); manage supportively
• Long half-life oxidant drugs (e.g., dapsone, t½ ~50 h): Prolonged oxidant stress requires repeated methylene blue dosing; consider cimetidine (inhibits CYP450-mediated formation of hydroxylamine metabolite) to reduce ongoing methemoglobin production

C. Hematopoietic Toxicity

• Hemolytic anemia - especially in G6PD-deficient patients (stop drug, supportive care, transfusion if severe)
• Aplastic anemia - rare, stop drug, haematology referral, supportive care
• Granulocytopenia / thrombocytopenia / leukemoid reactions - monitor CBC, stop drug

D. Hypersensitivity Reactions

• Stevens-Johnson syndrome (SJS) / Toxic Epidermal Necrolysis (TEN) - stop drug immediately, dermatology/burns unit referral, supportive wound care
• Fulminant hepatic necrosis - stop drug, liver function monitoring, consider N-acetylcysteine, hepatology referral
• Agranulocytosis - stop drug, granulocyte support, reverse barrier nursing
• Serum sickness-like reactions - antihistamines, corticosteroids if severe

• Immediately discontinue the sulfonamide
• Mild (rash only): antihistamines, topical corticosteroids, close monitoring
• Severe (anaphylaxis): epinephrine 0.3 mg IM, IV fluids, IV corticosteroids, antihistamines
• SJS/TEN: ICU-level supportive care, ophthalmology, wound management

E. CNS Toxicity

F. Metabolic Acidosis (Topical Mafenide Acetate)

2. General Decontamination Principles

• Oral ingestion (acute overdose): Activated charcoal (50 g in adults) if patient is alert and presents within 1-2 hours of ingestion; gastric lavage if massive ingestion and early presentation
• Dermal exposure: Remove contaminated clothing, wash with soap and water
• Gastric decontamination is of limited value in established methemoglobinemia due to time delay between ingestion and symptom onset

3. Supportive Care and Monitoring

4. Special Populations

• Neonates/near-term pregnancy: Sulfonamides displace bilirubin from albumin - avoid near delivery; risk of kernicterus
• G6PD deficiency: High risk of hemolytic crisis - avoid sulfonamides; if toxicity occurs, methylene blue will be ineffective
• HIV/AIDS patients: Very high rate of adverse reactions to TMP-SMX (fever, rash, leukopenia, hepatitis)
• Renal impairment: Reduce dose or avoid; risk of drug accumulation and crystalluria

• Katzung's Basic and Clinical Pharmacology (16th ed.) - Sulfonamides: Adverse Reactions, Urinary Tract Disturbances, Hematopoietic Disturbances
• Tintinalli's Emergency Medicine - Table 207-2: Management of Methemoglobinemia; Sulphemoglobinemia
• Goldman-Cecil Medicine - Methemoglobin treatment