Poison Study Guide

📖 Core Concepts Poison – any chemical that harms or kills a living organism, regardless of source. Toxin – a poison that is produced by a living organism (e.g., snake venom, bacterial exotoxin). Venom – a toxin that is actively injected (bite or sting); poisons are taken in passively (ingestion, inhalation, skin). Dose‑Response Relationship – toxicity severity depends on both the nature of the agent and the amount absorbed. Acute vs. Chronic Poisoning – Acute: single/short‑term exposure → rapid symptom onset. Chronic: repeated/continuous exposure → delayed, often cumulative effects. Decontamination Hierarchy – first‑line: activated charcoal (adsorbs most organic poisons). If ineffective → gastric lavage, nasogastric aspiration, or whole‑bowel irrigation. Supportive Care – primary treatment for most poisonings; maintain airway, breathing, circulation, and control seizures/shock. --- 📌 Must Remember Poison ≠ toxin ≠ venom – remember the origin and delivery method. Activated charcoal works except for metals (Na⁺, K⁺, Li⁺), alcohols, glycols, and corrosive acids/bases. Gastric lavage is only justified ≤ 1 hour after ingestion of a life‑threatening toxin. Cyanide → blocks cytochrome c oxidase → instant energy starvation. Methanol → metabolized → formaldehyde + formic acid → optic nerve damage. Potassium chloride overdose → stops cardiac electrical activity → asystole. Biomagnification: fat‑soluble poisons concentrate up food chains → predators at highest risk. Chelation is required for heavy metals (e.g., lead, mercury) but not for sodium/potassium. --- 🔄 Key Processes Activated Charcoal Administration Give 1 g/kg (max 50 g) orally within 1 hour of ingestion. Ensure airway protection; repeat dose if delayed‐release toxin is suspected. Gastric Lavage Procedure Insert large‑bore nasogastric tube. Flush with 200‑300 mL warm water/saline, aspirate, repeat up to 3‑5 times. Stop if > 1 hour has elapsed or if patient is unstable. Whole‑Bowel Irrigation (WBI) Administer polyethylene glycol (PEG) solution 1–2 L/h until clear effluent. Indications: sustained‑release drugs, lithium/iron poisoning, drug packets. Enhanced Elimination (e.g., Hemodialysis for Cyanide or Methanol) Identify toxin amenable to removal (low molecular weight, low protein binding). Initiate dialysis promptly; monitor electrolytes and acid‑base status. Management of Acute Cyanide Toxicity Provide 100% O₂, support circulation. Administer antidote kit (hydroxocobalamin + sodium thiosulfate) if available. --- 🔍 Key Comparisons Poison vs. Toxin → Origin: synthetic/any chemical vs. biologically produced. Poison vs. Venom → Delivery: passive (ingest/inhaled) vs. active injection. Activated Charcoal vs. Cathartics → Charcoal adsorbs → effective; cathartics no longer recommended (no outcome benefit). Acute vs. Chronic Poisoning → Exposure pattern: single/short vs. repeated/long; symptom timeline: immediate vs. delayed. Cyanide vs. Methanol Toxicity → Cyanide = cellular respiration block; Methanol = metabolite‑mediated ocular & metabolic acidosis. --- ⚠️ Common Misunderstandings “All poisons can be treated with charcoal.” – false; metals, alcohols, and corrosives are not adsorbed. “Ipecac is still used for vomiting.” – outdated; emesis is not recommended due to poor efficacy and aspiration risk. “Corrosive burns are poisons.” – corrosives cause local tissue destruction without systemic absorption; they are classified separately. “Chelation works for any metal.” – only specific chelators for particular metals; misuse can cause redistribution or renal injury. --- 🧠 Mental Models / Intuition “Absorption → Distribution → Metabolism → Excretion (ADME)” – if a toxin is not absorbed, decontamination (charcoal) is irrelevant; focus on local injury (e.g., corrosives). “Time is toxin” – the sooner you remove the poison, the less systemic absorption; prioritize interventions within the first hour. “Fat‑soluble = bioaccumulate” – think of lipophilic compounds (e.g., DDT) as “sticky” → they climb the food chain. --- 🚩 Exceptions & Edge Cases Lithium & Iron – not adsorbed by charcoal; require whole‑bowel irrigation or chelation. Ethylene Glycol – charcoal ineffective; nasogastric aspiration preferred early, followed by fomepizole or dialysis. Heavy‑metal chronic exposure – symptoms may be subtle; screening labs (blood/urine levels) are essential before starting chelation. --- 📍 When to Use Which | Situation | First‑line Treatment | Backup / Adjunct | |-----------|---------------------|------------------| | Recent ingestion of unknown organic toxin (<1 h) | Activated charcoal | Gastric lavage (if life‑threatening) | | Ingestion of sustained‑release tablet or drug packet | Whole‑bowel irrigation | Activated charcoal (if partially adsorbable) | | Suspected cyanide or methanol poisoning | Supportive care + specific antidote (hydroxocobalamin / fomepizole) | Hemodialysis (especially methanol) | | Heavy‑metal (lead, mercury) chronic exposure | Chelation (e.g., dimercaprol, EDTA) | Supportive care, monitor renal function | | Corrosive acid/base ingestion | No decontamination; immediate airway protection | Endoscopy to assess extent of injury | --- 👀 Patterns to Recognize Rapid neuromuscular paralysis → think nerve agents or potassium chloride overdose. “Methyl‑” smell + visual disturbances → suspect methanol; check for anion gap metabolic acidosis. Sudden cardiovascular collapse after IV infusion → consider potassium chloride or massive calcium channel blocker overdose. Bilateral optic neuropathy after ingestion → classic for methanol or ethylene glycol. Progressive weakness, ataxia, and tremor in a child → look for heavy‑metal (lead) chronic exposure. --- 🗂️ Exam Traps “Activated charcoal works for all ingested substances.” – trap: metals, alcohols, acids/bases are exceptions. “All corrosive injuries are treated with charcoal.” – trap: corrosives destroy tissue locally; charcoal offers no benefit. “Ipecac is the best way to induce vomiting.” – trap: modern guidelines have removed ipecac from standard practice. “Gastric lavage is safe up to 4 hours post‑ingestion.” – trap: effective only ≤ 1 hour and only for life‑threatening amounts. “All heavy‑metal poisoning requires chelation.” – trap: chelation is indicated only when blood levels exceed toxic thresholds; otherwise, observation may be appropriate. ---