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sulfonamide sulpha drug poisoning case study clinical features treatment
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I have enough information from the library and web results to construct a solid, reality-based case study. Here it is:
Reality-Based Case Study: Sulpha (Sulfonamide) Poisoning
Patient Profile
Patient: 28-year-old male, agricultural worker, HIV-negative
Presenting complaint: High fever, generalized skin blistering, dark-coloured urine, decreased urine output - 5 days after starting Co-trimoxazole (Trimethoprim + Sulfamethoxazole 960 mg twice daily) prescribed by a local clinic for a urinary tract infection.
Presenting complaint: High fever, generalized skin blistering, dark-coloured urine, decreased urine output - 5 days after starting Co-trimoxazole (Trimethoprim + Sulfamethoxazole 960 mg twice daily) prescribed by a local clinic for a urinary tract infection.
Background
The patient had been prescribed Co-trimoxazole (a sulphonamide combination drug) for a suspected UTI. He was a slow acetylator - a genetic phenotype common in certain South Asian and African populations - which significantly reduces the liver's ability to detoxify reactive sulphonamide metabolites, dramatically increasing the risk of toxicity. He self-medicated for 5 days without follow-up.
Clinical Presentation
| Feature | Finding |
|---|---|
| Temperature | 39.8°C (febrile) |
| Skin | Widespread blistering, mucosal erosions - lips, oral cavity, conjunctivae |
| Urine | Dark brown, reduced output (<300 mL/24 hrs) |
| Eyes | Bilateral conjunctival injection, purulent discharge |
| SpO₂ | 91% on room air (chocolate-brown blood on venepuncture) |
| Rash extent | ~35% body surface area involvement |
Investigations
| Investigation | Result | Significance |
|---|---|---|
| Urine microscopy | Sulphonamide crystals (fan/sheaf shaped), RBCs | Crystalluria - renal tubular obstruction |
| Serum creatinine | 4.8 mg/dL (baseline ~0.9) | Acute kidney injury |
| Haemoglobin | 7.2 g/dL | Haemolytic anaemia |
| Blood film | Heinz bodies, fragmented RBCs | Oxidative haemolysis |
| Methemoglobin level | 22% (normal <1%) | Methemoglobinemia |
| LFTs | AST 320, ALT 280, ALP raised | Drug-induced hepatotoxicity |
| Skin biopsy | Full-thickness epidermal necrosis | Toxic Epidermal Necrolysis (TEN) |
Diagnosis
Sulphonamide (Co-trimoxazole) poisoning presenting as:
- Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis (SJS-TEN overlap) - the most feared cutaneous complication, linked to slow acetylator status and reactive hydroxylamine metabolite accumulation
- Acute Kidney Injury (AKI) - due to crystalluria and direct tubular toxicity
- Methemoglobinemia - oxidative conversion of haemoglobin iron (Fe²⁺ → Fe³⁺) by sulphonamide metabolites
- Haemolytic Anaemia - oxidative red cell damage (Heinz body formation)
- Drug-Induced Liver Injury (DILI)
Pathophysiology (Brief)
Sulphonamides are metabolised in the liver via two pathways:
- Acetylation (N-acetyltransferase): Safe metabolites - fast acetylators are protected
- CYP450 oxidation: Produces hydroxylamine metabolites - directly toxic to RBCs and skin keratinocytes
In slow acetylators, the oxidative pathway dominates, producing excess toxic metabolites that cause:
- Oxidative haemolysis + Heinz bodies
- Methemoglobin formation (Fe³⁺ Hb cannot carry O₂)
- Immune-mediated keratinocyte destruction (SJS/TEN)
- Crystallization in renal tubules at acidic urine pH → AKI
Management
| Step | Action |
|---|---|
| Stop the drug immediately | Withdraw Co-trimoxazole without delay |
| Methemoglobinemia | IV Methylene blue 1-2 mg/kg over 5 mins (acts as cofactor for NADPH-dependent reduction) |
| Skin/TEN care | Transfer to burns unit; IV fluids, wound care, ophthalmology consult |
| AKI | IV fluid hydration; alkalinize urine (NaHCO₃) to dissolve crystals; renal replacement therapy if severe |
| Haemolytic anaemia | Blood transfusion if Hb <7 g/dL; monitor G6PD status |
| Hepatotoxicity | N-acetylcysteine (antioxidant support); stop hepatotoxic co-medications |
| Infection control | Broad-spectrum antibiotics for secondary skin infection; strict barrier nursing |
| Corticosteroids in TEN | Controversial - most guidelines do not recommend routinely; IVIg or cyclosporine may be considered |
Outcome
The patient was managed in an ICU-level burns unit. Methylene blue reversed the methemoglobinemia within 2 hours. AKI resolved over 10 days with fluids and alkalinization. Skin re-epithelialization took 3 weeks. He was discharged with permanent corneal scarring of the right eye and mild residual renal impairment.
Key Learning Points
- Slow acetylator status is the most important pharmacogenetic risk factor for sulphonamide toxicity - common in South Asian and African populations.
- SJS/TEN from sulphonamides carries a mortality of 10-50% and demands immediate drug withdrawal - every hour of continued exposure worsens outcomes.
- Crystalluria is pathognomonic of sulpha nephrotoxicity - always ensure adequate hydration and urine alkalinization.
- Methemoglobinemia should be suspected in any patient on sulpha drugs with cyanosis unresponsive to oxygen, especially when blood appears chocolate-brown.
- Sulphonamides remain one of the most common causes of drug-induced acute liver failure, contributing 5-10% of cases in major series.
- Co-trimoxazole should be used with caution (or avoided) in known slow acetylators, G6PD-deficient individuals, and patients with pre-existing renal impairment.
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