A 28-year-old woman is brought to the hospital 18 hours after intentional ingestion of white powder (suspected arsenic trioxide) in a suicide attempt. She is now haemodynamically stable after aggressive fluid resuscitation. Serum arsenic level is 85 mcg/dL (normal < 15 mcg/dL). Urine arsenic is 120 mcg/L. She has mild peripheral neuropathy and skin changes (Mees' lines). What is the most appropriate next step in management?

Explanation

## Clinical Context This is a case of **acute arsenic poisoning with systemic manifestations** (peripheral neuropathy, Mees' lines suggesting significant arsenic burden). The patient is haemodynamically stable 18 hours post-ingestion, making her eligible for chelation therapy. Elevated serum arsenic (85 mcg/dL) and urine arsenic (120 mcg/L) confirm significant arsenic toxicity requiring active chelation. ## Chelation Agent Selection **Key Point:** In the Indian clinical context (NEET PG / INI-CET jurisdiction), **DMSA (meso-2,3-dimercaptosuccinic acid)** is the chelation agent of choice for arsenic poisoning because: 1. **DMPS is NOT approved or routinely available in India** — making it an impractical answer in the Indian examination and clinical context 2. **DMSA is orally bioavailable**, safe, and effective for both acute and chronic inorganic arsenic poisoning 3. **Standard dosing:** 10 mg/kg orally three times daily for 5 days (may repeat after a 2-day rest period) 4. **Haemodynamically stable patients** with intact GI tract are ideal candidates for oral DMSA therapy 5. DMSA has a **favourable safety profile** compared to older agents (BAL/dimercaprol) and penicillamine ## Comparison of Chelation Agents | Feature | DMSA | DMPS | Penicillamine | |---------|------|------|---------------| | **Route** | Oral | IV/IM | Oral | | **Availability (India)** | ✅ Available | ❌ Not approved | ✅ Available | | **Best for** | Acute & chronic As, Pb | Acute inorganic As (where available) | Lead, Cu, Hg (not first-line for As) | | **Dosing** | 10 mg/kg TDS × 5 days | 3 mg/kg TDS × 5 days | 250 mg QID × 7 days | | **Adverse effects** | Mild (rash, GI upset) | Mild (taste, rash) | Serious (lupus-like, proteinuria) | ## Why Other Options Are Incorrect - **Option B (DMPS IV/IM):** Although DMPS has superior efficacy for acute inorganic arsenic in theory, it is **not approved or available in India**, making it an incorrect choice in the Indian clinical/examination context. - **Option C (Penicillamine):** Not the drug of choice for arsenic poisoning; primarily used for lead, copper (Wilson's disease), and mercury toxicity. Associated with serious adverse effects. - **Option D (Observe without chelation):** Incorrect — the patient has symptomatic arsenic toxicity (neuropathy, Mees' lines) with significantly elevated arsenic levels. Chelation is clearly indicated. ## Monitoring During Chelation **Clinical Pearl:** Chelation efficacy is monitored by: - **24-hour urine arsenic** before and after each course - **Clinical improvement** (neuropathy, skin changes resolve over weeks) - **Target:** Urine arsenic < 50 mcg/L indicates adequate chelation **High-Yield:** Mees' lines (transverse white bands on nails) are a classic sign of arsenic poisoning, typically appearing 4–6 weeks after significant exposure, suggesting this patient may have had prior or ongoing arsenic exposure before this acute ingestion event. [cite: Reddy & Murthy Forensic Medicine & Toxicology 34e Ch 18; KD Tripathi Essentials of Medical Pharmacology 8e; Park's Textbook of Preventive & Social Medicine 26e Ch 12]