# Poisoning, Antidotes, Chelators, Skin and Eye Drugs for NEET PG Pharmacology: Snakebite (MoHFW), Methylene Blue, Isotretinoin Source: https://tracknation.in/story/poisoning-antidotes-chelators-skin-and-eye-drugs-for-neet-pg-pharmacology-snakebite-mohfw-methylene-blue-isotretinoin (TrackNation — free UPSC notes with PYQs) > NEET PG Pharmacology: India's snakebite guideline (Big Four, 20WBCT, ASV dosing, neostigmine test, adrenaline for reactions), a poison-antidote table, chelators for iron, lead, arsenic, mercury and copper, cyanide and methaemoglobinaemia, flumazenil, physostigmine, isotretinoin, and timolol and latanoprost eye drops, with a diagram, hooks, vignette MCQs and cards. ## Start Here 🎯 **Exam priority: Very high.** *Expect: a snakebite with non-clotting blood or ptosis, the ASV dose, the antidote for iron, lead, cyanide, methanol or methaemoglobinaemia, flumazenil in a mixed overdose, isotretinoin in a young woman and timolol drops in an asthmatic.* CBME mapping: **PH 9**. Indian protocol: **MoHFW Standard Treatment Guidelines for Snakebite (2016)**. ## Snakebite (MoHFW) | **Step (MoHFW snakebite STG, 2016)** | **Detail** | | The Big Four | Common cobra, Russell's viper, saw-scaled viper, common krait | | First aid | Any tourniquet or ligature can be removed once an IV line is established | | 20WBCT | Blood in a clean, new, dry glass tube; report 'clotted' or 'not clotted' (never positive/negative); repeat hourly for 3 h, then 6-hourly to 24 h | | ASV — vasculotoxic | 10 vials; repeat if bleeding continues 1 hour after the first 10 vials | | ASV — neurotoxic | 10 vials over 30 min, a second 10 if no improvement in 1 hour; maximum 20 vials | | Neostigmine (AN) test | Atropine 0.6 mg then neostigmine 1.5 mg IV; neostigmine 0.5 mg with atropine every 30 min × 5; not in confirmed krait bite | | ASV reaction | Adrenaline 0.5 mg IM (children 0.01 mg/kg) | | Not available | Specific ASV for sea snake and pit viper bites | ## Antidotes at a Glance *Poisons and their antidotes, from the drugs' labels. Drawn by TrackNation.* - **Flumazenil** reverses benzodiazepines but can provoke withdrawal seizures — risk higher after a large cyclic antidepressant overdose. - **Methylene blue** treats acquired methaemoglobinaemia; boxed serotonin syndrome with serotonergic drugs; contraindicated in G6PD deficiency (haemolysis). - **Hydroxocobalamin** for cyanide: 5 g IV for adults. **Physostigmine** for central anticholinergic syndrome. ## Chelating Agents | **Chelator** | **Use (label)** | | Deferoxamine | Acute iron poisoning; transfusional iron overload (urine turns reddish) | | Dimercaprol (BAL) | Arsenic, gold, mercury; acute lead poisoning with calcium disodium EDTA | | Succimer | Lead poisoning in children ≥ 1 year with blood lead > 45 mcg/dL | | Calcium disodium EDTA | Lead poisoning (encephalopathy commoner in children) | | Penicillamine | Wilson's disease; cystinuria; severe rheumatoid arthritis | ## Skin and Eye Drugs - **Isotretinoin**: boxed — life-threatening birth defects; contraindicated in pregnancy; prescribed under iPLEDGE with two forms of contraception (or abstinence). - **Timolol eye drops** act systemically: contraindicated in asthma, severe COPD, sinus bradycardia, AV block, overt heart failure. - **Latanoprost**: increased brown iris pigmentation (likely permanent); longer, thicker, more eyelashes. ## Traps the Examiner Sets - 20WBCT is reported as clotted/not clotted, never positive/negative. - Neostigmine test is not given for a confirmed krait bite; max ASV 20 vials in neurotoxic bites. - Methylene blue is wrong in G6PD deficiency. - Lead in a child: succimer (blood lead > 45) or calcium disodium EDTA. - Timolol drops can trigger asthma. ## Memory Hooks & Shortcuts *Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.* - 🧠 **Big Four: Cobra, Krait, Russell, Saw-scaled (CKRS)** — India's main venomous snakes - 🧠 **Twenty minutes, Two answers: clotted or not** — 20WBCT reporting - 🧠 **Ten, then ten, then stop (20)** — neurotoxic ASV dosing - 🧠 **No AN for the krait** — neostigmine test not in krait bites - 🧠 **Iron: De-FEROX-amine** — iron chelator - 🧠 **Blue is bad for G6PD** — methylene blue contraindication - 🧠 **Timolol: Tight chest** — bronchospasm from eye drops ## Rapid-Revision Cards - Cobra, Russell's viper, saw-scaled viper, krait. - Clean dry glass tube; clotted / not clotted; hourly × 3 then 6-hourly. - 10 vials; repeat if bleeding at 1 h. - 10 + 10; max 20 vials. - Atropine 0.6 + neostigmine 1.5 mg IV; not in krait bite. - Adrenaline 0.5 mg IM. - N-acetylcysteine. - Fomepizole. - Flumazenil (seizures with TCA). - Deferoxamine (reddish urine). - Succimer if > 45 mcg/dL; Ca-Na2 EDTA. - Dimercaprol. - Penicillamine. - Hydroxocobalamin 5 g IV. - Methylene blue; not in G6PD; serotonin syndrome. - Physostigmine. - Teratogen; iPLEDGE; two contraceptives. - Not in asthma, bradycardia, AV block, HF. - Brown iris (permanent); eyelash growth. ## Sources *Facts in this article were checked against these documents.* - Standard Treatment Guidelines: Snakebite — Directorate General of Health Services, MoHFW (with NHSRC), June 2016 (link) - Prescribing labels: Acetadote, naloxone, Protopam, fomepizole, Lanoxin, flumazenil, deferoxamine, BAL in Oil, Chemet, edetate calcium disodium, Cuprimine, Anticholium, Cyanokit, ProvayBlue, isotretinoin, brimonidine-timolol, Xalatan — DailyMed, US National Library of Medicine, current labels, accessed November 2026 (link) - Competency Based Undergraduate Curriculum, Pharmacology (PH 9) — National Medical Commission, 2024 ## Test Yourself: Practice Questions Twenty-four questions in NEET PG style, most of them clinical vignettes. ## Practice Questions (NEET PG pattern) *Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.* **Q1.** A farmer bitten by a snake has abnormal bleeding; blood in a clean dry glass tube is still liquid at 20 minutes. Per MoHFW, the result is reported as - (a) 'positive' - (b) 'borderline' - (c) 'negative' - (d) 'not clotted' — vasculotoxic envenomation **Answer: (d)** — Never write positive/negative; repeat hourly for 3 h, then 6-hourly to 24 h. **Q2.** In that vasculotoxic bite, after the first 10 vials of ASV bleeding continues at 1 hour. MoHFW advises - (a) a repeat dose of ASV - (b) heparin - (c) vitamin K only - (d) stopping ASV **Answer: (a)** — Repeat ASV if bleeding persists one hour after the first 10 vials. **Q3.** A boy with ptosis and difficulty breathing after a cobra bite needs ASV. The MoHFW regimen is - (a) 50 vials at once - (b) 10 vials over 30 min, then 10 more if no improvement in 1 hour (max 20) - (c) no ASV — neostigmine alone - (d) 2 vials only **Answer: (b)** — Maximum 20 vials for neurotoxic envenoming. **Q4.** In neurotoxic envenoming, the 'AN' test uses - (a) atropine alone - (b) adrenaline and naloxone - (c) neostigmine alone without atropine - (d) atropine 0.6 mg then neostigmine 1.5 mg IV, neostigmine 0.5 mg with atropine every 30 min × 5 **Answer: (d)** — MoHFW snakebite STG. **Q5.** The AN (neostigmine) test should not be given when - (a) a cobra bite is suspected - (b) a krait bite is confirmed - (c) the patient is a child - (d) the patient has ptosis **Answer: (b)** — MoHFW STG. **Q6.** During ASV infusion a patient develops an allergic reaction. MoHFW's treatment is - (a) stop ASV permanently and give nothing - (b) IV calcium - (c) adrenaline 0.5 mg IM (children 0.01 mg/kg) - (d) oral cetirizine only **Answer: (c)** — Adrenaline for ASV reactions. **Q7.** India's 'Big Four' venomous snakes are - (a) common cobra, Russell's viper, saw-scaled viper, common krait - (b) only vipers - (c) king cobra, pit viper, sea snake, python - (d) rat snake, cobra, krait, mamba **Answer: (a)** — MoHFW STG. **Q8.** A toddler swallows many of her mother's iron tablets. The specific chelator is - (a) deferoxamine - (b) succimer - (c) dimercaprol - (d) penicillamine **Answer: (a)** — Deferoxamine turns the urine reddish. **Q9.** A 3-year-old has a blood lead of 52 mcg/dL without encephalopathy. A labelled oral chelator is - (a) penicillamine - (b) deferoxamine - (c) methylene blue - (d) succimer **Answer: (d)** — Children ≥ 1 year with blood lead > 45 mcg/dL. **Q10.** A worker with arsenic poisoning needs chelation. The labelled drug is - (a) flumazenil - (b) dimercaprol (BAL) - (c) deferoxamine - (d) fomepizole **Answer: (b)** — BAL: arsenic, gold, mercury; with calcium disodium EDTA for acute lead poisoning. **Q11.** A teenager with Wilson's disease is started on a chelator. The classic one is - (a) penicillamine - (b) dimercaprol - (c) deferoxamine - (d) succimer **Answer: (a)** — Also cystinuria and severe rheumatoid arthritis. **Q12.** After smoke inhalation in a house fire, cyanide poisoning is suspected. Give - (a) deferoxamine - (b) flumazenil - (c) hydroxocobalamin 5 g IV - (d) methylene blue **Answer: (c)** — Cyanokit label. **Q13.** A patient with acquired methaemoglobinaemia is known to have G6PD deficiency. Methylene blue is - (a) contraindicated (risk of haemolytic anaemia) - (b) given orally only - (c) the drug of choice - (d) safe at double dose **Answer: (a)** — ProvayBlue label. **Q14.** A patient on an SSRI is given IV methylene blue and develops agitation and hyperthermia. The boxed warning is - (a) QT prolongation - (b) serotonin syndrome with serotonergic drugs - (c) hepatotoxicity - (d) anaphylaxis **Answer: (b)** — ProvayBlue boxed warning. **Q15.** An unconscious patient has taken unknown pills, possibly benzodiazepines and a tricyclic. Flumazenil is risky because - (a) it has no effect - (b) it can provoke seizures, especially after a large cyclic antidepressant overdose - (c) it is an opioid - (d) it causes respiratory depression **Answer: (b)** — Flumazenil label. **Q16.** A child has central anticholinergic syndrome after a plant poisoning. A labelled antidote is - (a) neostigmine - (b) pralidoxime - (c) atropine - (d) physostigmine **Answer: (d)** — Anticholium label. **Q17.** A man drinks illicit liquor and develops visual blurring and acidosis. The labelled antidote is - (a) N-acetylcysteine - (b) flumazenil - (c) fomepizole - (d) naloxone **Answer: (c)** — Fomepizole for methanol or ethylene glycol. **Q18.** Pralidoxime works in organophosphate poisoning by - (a) blocking muscarinic receptors - (b) stimulating nicotinic receptors - (c) reactivating phosphorylated cholinesterase - (d) binding the organophosphate in the gut **Answer: (c)** — Protopam label. **Q19.** A 20-year-old woman starting isotretinoin for nodular acne must - (a) take it only in winter - (b) use two forms of contraception (or abstain) under iPLEDGE — it causes severe birth defects - (c) only avoid sun - (d) take folic acid only **Answer: (b)** — Boxed: contraindicated in pregnancy. **Q20.** An asthmatic with glaucoma is prescribed timolol eye drops and develops severe wheeze. The label - (a) contraindicates timolol in bronchial asthma - (b) says eye drops have no systemic effect - (c) blames the glaucoma - (d) recommends a higher dose **Answer: (a)** — Also sinus bradycardia, AV block, overt heart failure. **Q21.** A patient using latanoprost in one eye notices that eye's iris has turned browner. The label says this change is - (a) likely permanent - (b) a sign of infection - (c) due to cataract - (d) always reversible **Answer: (a)** — Eyelash growth changes are usually reversible. **Q22.** Specific antivenom for which bites is not available in India? - (a) krait - (b) sea snake and pit viper - (c) cobra - (d) Russell's viper **Answer: (b)** — MoHFW STG; available ASV may help by cross-reaction. **Q23.** Dimercaprol is used for acute lead poisoning together with - (a) penicillamine - (b) methylene blue - (c) deferoxamine - (d) calcium disodium EDTA **Answer: (d)** — BAL label. **Q24.** N-acetylcysteine (Acetadote) is indicated to - (a) treat iron overdose - (b) reverse opioid overdose - (c) chelate lead - (d) prevent or lessen liver injury after a hepatotoxic paracetamol dose **Answer: (d)** — Acetadote label. ### Active Recall From memory: outline MoHFW snakebite management (Big Four, 20WBCT, ASV doses for vasculotoxic and neurotoxic bites, the AN test, treating ASV reactions); match common poisons to their antidotes and chelators; and give the key warnings for methylene blue, flumazenil, isotretinoin, timolol and latanoprost.