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|Drug Toxicity with Specific Antidotes
Quinine is a medication used mainly for chloroquine-resistant malaria and occasionally nocturnal leg cramps. ❌ At higher doses it is toxic, producing the syndrome of cinchonism - a combination of auditory, visual, neurological, and cardiovascular disturbances. Prompt recognition and management are vital, as toxicity can progress to blindness, arrhythmias, or death.
ℹ️ About
- Quinine (a natural alkaloid from the cinchona tree 🌳) was the first effective anti-malarial; still used against chloroquine-resistant Plasmodium falciparum.
- Sometimes prescribed (though controversial) for nocturnal leg cramps; carries significant risk of hypersensitivity and toxicity.
- Structurally and pharmacologically related to quinidine, hence significant cardiac sodium channel blocking effects.
Pathophysiology 🧬
- Neuro-ototoxicity: Direct effects on auditory & optic nerves → tinnitus, hearing loss, blurred vision, blindness (vasospasm of retinal arterioles, retinal oedema, optic atrophy).
- Cardiotoxicity: Class Ia antiarrhythmic effect (Na⁺ channel block + K⁺ channel block) → widened QRS, prolonged QTc, torsades de pointes, VF. ⚡
- Metabolic effects: Stimulates pancreatic insulin release → profound hypoglycaemia, especially in children and pregnant women. 🍬⬇️
- Haematological: Quinine hypersensitivity can trigger haemolysis, thrombocytopenia, and DIC (“Blackwater fever”). ⚠️
Clinical Presentation 🩺
- Cinchonism: Tinnitus, hearing loss, headache, dizziness, nausea, visual disturbances (blurred vision, photophobia, blindness). 🎧👁️
- Neurological: Confusion, delirium, tremor, seizures, coma, respiratory depression.
- Cardiac: Hypotension, bradycardia or tachyarrhythmias, wide QRS, prolonged QT, torsades de pointes, VF. ❤️
- Metabolic: Hypoglycaemia (may be recurrent and prolonged).
- Other: Fever, tachypnoea, acute renal injury, hypersensitivity reactions (rash, haemolysis).
Investigations 🔬
- ECG: Widened QRS (>120 ms), prolonged QTc, risk of torsades/VF.
- Blood glucose: Monitor frequently - hypoglycaemia may recur despite treatment.
- U&E, renal function: To detect AKI and electrolyte derangements.
- LFTs & FBC: To assess haemolysis, thrombocytopenia, or DIC in hypersensitivity cases.
- Quinine levels: Rarely available, not essential to management.
Management 💉
- Immediate decontamination: Activated charcoal (50 g, repeated doses for large ingestion). Gastric lavage if very early & airway protected.
- Cardiac support:
- Atropine 0.6 mg IV for symptomatic bradycardia; pacing if refractory.
- If QRS >120 ms → IV sodium bicarbonate (target pH 7.45–7.55). 🧪
- Magnesium sulfate for torsades de pointes. ⚡
- Neurological: Benzodiazepines (e.g. lorazepam, diazepam) for seizures.
- Hypoglycaemia: IV dextrose; repeated boluses or infusion as quinine stimulates recurrent insulin release.
- Haemodialysis: Limited role (quinine is highly protein bound) but may help in massive overdose with renal failure.
- Supportive: IV fluids, electrolyte correction, continuous cardiac monitoring, early ITU involvement.
Prognosis 📉
- Mortality is dose-dependent; survival possible with aggressive support if detected early.
- Visual loss is often permanent due to retinal artery spasm and optic atrophy. 👁️❌
- Hypoglycaemia and arrhythmias are the main causes of death.
Clinical Pearls ✨
- 🚑 Classic triad in exams: Visual disturbance + Tinnitus/hearing loss + Arrhythmias → think Quinine (cinchonism).
- 🍬 Hypoglycaemia is common, prolonged, and may require continuous glucose infusion - especially in pregnant women.
- ❤️ ECG resembles TCA/quinidine poisoning → sodium bicarbonate is lifesaving.
- 👩⚕️ Visual loss often irreversible → emphasise early recognition and prevention.
