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Five classical toxidromes a clinician reads at the bedside, paired with the specific antidotes actually stocked in Indian government hospital pharmacies.
A toxidrome is the cluster of vital-sign, pupil, skin and mental-status findings that points to a class of poison before any laboratory result arrives. Five classical patterns carry most of the bedside workload in an Indian emergency department: cholinergic (organophosphate, carbamate, certain mushrooms), anticholinergic (Datura, tricyclic antidepressants, antihistamines), opioid (heroin, tramadol, fentanyl), sympathomimetic (amphetamine, cocaine, methamphetamine) and sedative-hypnotic (benzodiazepines, barbiturates, ethanol). Each pattern has a defined first-line antidote, a defined supportive package and a defined window in which the antidote actually changes outcome.
The harder truth on the ground is that recognising the toxidrome is the easy half. The decisive half is whether the right antidote is on the trolley at the right strength. Atropine, naloxone, N-acetylcysteine and polyvalent anti-snake venom (ASV) are stocked across most Indian government district hospitals; fomepizole, hydroxocobalamin and digoxin-Fab fragments are not. The National Poisons Information Centre at AIIMS Delhi runs a 24x7 helpline on 011-26593677, and the Madras Medical College NPIC mirrors that role in the south. This page maps the five toxidromes onto the actual antidote shelf an Indian house officer will find at 02:00.
Pupil, skin, secretions, bowel and bladder, mental status. Five lines decide the class.
The bedside toxidrome examination is five lines long and runs in the same order every time. Pupils first (miosis, mydriasis, normal). Skin next (dry, sweaty, flushed, cyanosed). Pulmonary secretions and bowel sounds (wet versus dry). Vital signs (heart rate, blood pressure, respiratory rate, temperature). Mental status last (agitated, depressed, normal). The cluster, not any single finding, identifies the class.
| Toxidrome | Classic agents | Pupils | Skin and secretions | Vitals | Mental status |
|---|---|---|---|---|---|
| Cholinergic | Organophosphate (chlorpyrifos, monocrotophos), carbamate, Amanita muscaria | Miosis (pinpoint) | Wet: lacrimation, salivation, bronchorrhoea, sweating | Bradycardia, hypotension, bronchospasm, fasciculations | Drowsy progressing to coma |
| Anticholinergic | Datura stramonium, atropine, antihistamines, tricyclic antidepressants | Mydriasis | Hot, dry, flushed, no sweat | Tachycardia, hyperthermia, urinary retention, absent bowel sounds | Agitated delirium, hallucinations |
Drying the chest is the goal. Pupil size is not.
The cholinergic toxidrome is produced by inhibition of acetylcholinesterase. Acetylcholine accumulates at muscarinic, nicotinic and central receptors. The muscarinic side gives DUMBBELS (Diarrhoea, Urination, Miosis, Bronchospasm and Bronchorrhoea, Bradycardia, Emesis, Lacrimation, Salivation). The nicotinic side gives fasciculations, muscle weakness and tachycardia (which can mask the muscarinic bradycardia). Central effects give seizures, coma and central respiratory failure.
One specific antidote per class, with the Indian brand on the shelf.
The anticholinergic patient is hot, dry, red, blind and mad: hyperthermic, anhydrotic, flushed, with fixed dilated pupils and an agitated delirium. In India the commonest agent is Datura stramonium (dhatura), ingested deliberately as an intoxicant or accidentally as a roadside criminal sedative used to rob travellers. Tricyclic antidepressant overdose (amitriptyline, imipramine) and first-generation antihistamines (chlorpheniramine, diphenhydramine) follow.
Treatment of anticholinergic poisoning is mostly supportive: benzodiazepines for agitation, active cooling for hyperthermia, urinary catheterisation, and cardiac monitoring (tricyclics widen the QRS and can produce ventricular arrhythmias treated with sodium bicarbonate). Physostigmine, the specific antidote, is rarely available in Indian hospitals and is reserved for severe central toxicity without QRS widening; the seizure and asystole risk has kept it off most state formularies.
Opioid toxidrome is the easiest to recognise and the most rewarding to treat. The triad of pinpoint pupils, respiratory depression and depressed mental status is pathognomonic. Naloxone (sold in India as Nalox, Naltima and as generic ampoules of 0.4 mg/ml) reverses the picture within 60 to 90 seconds.
Sympathomimetic toxidrome (amphetamine, methamphetamine, MDMA, cocaine, synthetic cathinones) shares mydriasis and tachycardia with the anticholinergic pattern but the patient is diaphoretic and has active bowel sounds. Treatment is benzodiazepines in escalating doses for agitation, hypertension and tachycardia; active cooling for hyperthermia (mortality climbs steeply above 40 degrees Celsius); and avoidance of beta-blockers as a single agent because unopposed alpha stimulation can worsen coronary spasm in cocaine toxicity.
What is actually on the shelf, and what is not.
Beyond the five toxidromes, several poisons have specific antidotes that change outcome decisively. The shelf reality in India splits these into three tiers: routinely stocked across district hospitals, stocked at tertiary centres only, and effectively unavailable outside a handful of metros.
| Poison | Specific antidote | Indian dose and stocking reality |
|---|---|---|
| Paracetamol (acetaminophen) | N-acetylcysteine (NAC) | IV NAC 150 mg/kg over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours. The 21-hour AIIMS protocol. Mucomyst and generic IV NAC ampoules stocked at every tertiary hospital. |
| Opioids | Naloxone (Nalox, Naltima) | 0.4 to 2 mg IV titrated. Stocked across government hospitals and most CHCs; less reliable at PHCs. |
| Benzodiazepines (pure overdose) | Flumazenil (Anexate, Romazicon) | 0.2 mg IV every minute up to 1 mg. Stocked at tertiary anaesthesia units; rarely used because of mixed-ingestion risk. |
| Methanol, ethylene glycol | Fomepizole or ethanol | Fomepizole is not routinely stocked in India. The working antidote in hooch tragedies (Bihar 2016, Gujarat 2022, Tamil Nadu 2023) is oral or IV ethanol titrated to a blood level around 100 to 150 mg/dl, plus haemodialysis. |
ABC, decontamination, toxidrome, antidote, disposition.
The first sixty minutes after a poisoned patient arrives at an Indian district emergency room follows a stable sequence. The team has limited investigation back-up (often no immediate toxicology screen, no ABG machine outside the ICU, point-of-care glucose and not much else), so the toxidrome and the history carry most of the diagnostic weight.
Five common failure modes and how to avoid them.
The literature on Indian poisoning outcomes consistently identifies a handful of avoidable errors. Recognising them is half the battle.
Under-atropinisation is the commonest. Doctors stop atropine because the pupils have dilated or the heart rate is 110. Both are wrong end points. The patient must have a dry chest and clear lungs. A heart rate of 110 in an organophosphate case is the goal, not a problem. Audit data from medical college emergency departments in Maharashtra and Karnataka have repeatedly shown that adequate atropinisation reduces mortality from around 25 percent to under 10 percent in moderate-severity organophosphate poisoning.
Late pralidoxime is the second. The 36-hour window is shorter than most people remember. Once the enzyme-OP bond ages, no oxime will reactivate it and the patient is committed to a long course of intermediate syndrome and neuropathy.
Inappropriate gastric lavage is the third. Lavage after one hour, lavage without a protected airway in a drowsy patient, lavage with cold water in a patient with corrosive ingestion. The procedure is no longer routine; the indications have narrowed. Aspiration pneumonia from a botched lavage often kills more patients than the original poison.
Empirical flumazenil in mixed overdose is the fourth. Flumazenil in a patient who has co-ingested a tricyclic can precipitate ventricular tachycardia. Flumazenil in a chronic benzodiazepine user can precipitate seizures. The Indian default is to support the airway and skip the antagonist.
Failure to repeat ASV is the fifth. After the initial 10 vials, the WBCT should be rechecked at six hours. If it is still positive, give another 10 vials. Several rural Indian deaths from Russell's viper envenomation have been traced back to a single round of ASV followed by no clinical reassessment.
A sixth error, less often discussed but routine in audits, is reliance on the prescription found on the patient. A bottle of organophosphate next to an unconscious patient does not rule out a paracetamol co-ingestion, an alcohol level that needs separate treatment, or a separate undisclosed antidepressant ingestion. The clinical pattern, the toxidrome and the timeline matter at least as much as the bottle. Patients and families sometimes hand over the wrong bottle, and substance availability at the scene reflects what was easily reachable rather than what was actually swallowed. Treat the patient, not the bottle, and keep the toxicology screen in mind for the cases that do not fit.
A 22-year-old farmer presents with pinpoint pupils, copious oral secretions, bilateral lung crepitations, heart rate 48, and fasciculations of the eyelids and tongue. The toxidrome and the first-line antidote pair is:
| Opioid | Heroin, morphine, tramadol, fentanyl, codeine | Pinpoint miosis | Cool, dry | Bradypnoea (the lethal sign), hypotension, hypothermia | Depressed, stuporous, coma |
| Sympathomimetic | Amphetamine, methamphetamine, cocaine, MDMA | Mydriasis | Diaphoretic (this is the differentiator from anticholinergic) | Tachycardia, hypertension, hyperthermia | Agitated, psychotic, paranoid |
| Sedative-hypnotic | Benzodiazepines (alprazolam, diazepam), barbiturates, ethanol, GHB | Normal or small | Cool, dry | Hypotension, bradypnoea, hypothermia, hyporeflexia | Depressed, stuporous |
Two pairs trip up new registrars. Anticholinergic and sympathomimetic both give mydriasis and tachycardia, but the anticholinergic patient is bone dry and the sympathomimetic patient is drenched in sweat. Cholinergic and opioid both give miosis and coma, but the cholinergic patient is wet (audible crackles across the chest, drooling, urine on the sheet) and the opioid patient is dry with a respiratory rate of four. A registrar who learns those two discriminators in the first month of casualty posting will be right on the class about 80 percent of the time, which is enough to choose the antidote.
The cholinergic pattern is the highest-yield single toxidrome in Indian practice because organophosphate self-poisoning still dominates rural emergency presentations across Maharashtra, Andhra Pradesh, Telangana, Karnataka and West Bengal. The Indian Council of Medical Research Burden of Suicide study and successive NCRB Accidental Deaths and Suicides reports have placed pesticide ingestion among the top three suicide methods nationally for over a decade. The agents have shifted over the years (parathion and methyl parathion gave way to chlorpyrifos and monocrotophos as regulation tightened, and aluminium phosphide carved out its own large share in northern grain belts) but the toxidrome remains the same and the bedside drill remains the same.
The opioid toxidrome has changed shape too. Urban Indian emergency departments now see a steady trickle of tramadol overdose in young adults, often co-ingested with alprazolam, which complicates the classical triad because the benzodiazepine deepens respiratory depression but does not give miosis. Heroin and brown sugar overdose still appears in Mumbai, Delhi, Punjab and the northeast. Transdermal fentanyl misuse, common in Western emergency literature, is rare in Indian government hospitals but has been reported in metro private practice and is rising. Recognising the toxidrome in any of these patterns is the same: pinpoint pupils, depressed breathing, depressed mental status, dry skin.
Carbamate poisoning (propoxur, carbaryl, the household cockroach gels) produces the same toxidrome but the inhibition is spontaneously reversible, so the course is shorter and pralidoxime is not routinely indicated. Amanita muscaria and a handful of other mushrooms produce a pure muscarinic picture treated with atropine alone. The same applies to a class of plants containing pilocarpine-like alkaloids, which Indian rural patients occasionally consume in home remedies; the picture is short, self-limiting and responds to small doses of atropine.
The Indian organophosphate casebook has a few specific patterns worth noting. Chlorpyrifos (sold as Sumithion and a long list of generic formulations) is a slowly hydrolysed thiophosphate that produces a long, drawn-out clinical course with high pralidoxime requirements. Monocrotophos (Nuvacron, Azodrin) is fast acting and high mortality. Methyl parathion (Folidol-M), still in some informal supply chains, is among the most lethal agents per millilitre swallowed. Dichlorvos (Nuvan) is volatile and produces both ingestional and inhalational poisoning, the latter sometimes seen in workers cleaning empty containers without ventilation. Each of these responds to the same atropine plus pralidoxime backbone, but the dose, duration and ICU stay vary widely.
Sedative-hypnotic toxidrome is the most familiar urban presentation: alprazolam, diazepam, clonazepam, alone or with alcohol. Supportive care covers most cases. Flumazenil (the specific benzodiazepine antagonist, 0.2 mg IV every minute up to 1 mg) reverses pure benzodiazepine overdose but is rarely used in Indian practice. The reason is straightforward: most Indian benzodiazepine overdoses are mixed (typically with tricyclics, sedating antipsychotics or ethanol) and flumazenil can unmask seizures or arrhythmias from the co-ingestant. The risk-benefit calculation has pushed Indian protocols toward airway support and observation rather than reversal.
Ethanol deserves a separate paragraph because it sits inside the sedative-hypnotic toxidrome but with extra dimensions. The hypoglycaemia that accompanies acute alcohol intoxication, particularly in malnourished or chronic users, has to be ruled out at the door with a point-of-care glucose. Wernicke encephalopathy in a chronic user can be precipitated by a glucose bolus given before thiamine; the Indian default is to give 100 mg IV or IM thiamine before any glucose load in a comatose patient with a history of alcohol use. Methanol contamination of country liquor is the other concern. Any cluster of patients arriving from the same village or the same hooch source with sedation, blurred vision, metabolic acidosis or breathlessness is treated as methanol until proven otherwise, and the working antidote is intravenous ethanol with haemodialysis as covered in Section 4.
| Cyanide | Sodium thiosulphate plus sodium nitrite; hydroxocobalamin (Cyanokit) is gold standard | Thiosulphate 12.5 g IV plus nitrite 300 mg IV. Cyanokit is stocked only at AIIMS and a few private metro hospitals because of cost. |
| Methaemoglobinaemia (nitrates, dapsone, aniline dyes) | Methylene blue | 1 to 2 mg/kg IV over 5 minutes. Stocked at all medical college hospitals; G6PD status should be checked before repeat dosing. |
| Organophosphate, carbamate | Atropine plus pralidoxime (2-PAM) | See Section 2. Atropine is universally stocked; pralidoxime supply is reliable at medical college level, variable at district level. |
| Heavy metals: arsenic, mercury, lead | DMSA (succimer), DMPS, BAL (dimercaprol), Ca-EDTA, D-penicillamine | BAL injection and Ca-EDTA stocked at toxicology referral centres. Oral DMSA available through approved suppliers. Chelation is initiated at AIIMS, PGIMER Chandigarh, CMC Vellore, JIPMER. |
| Aluminium phosphide (Celphos, Quickphos) | No specific antidote | Supportive only: intravenous magnesium sulphate, GI decontamination with sodium bicarbonate lavage, vasopressors, insulin-glucose for shock, occasionally trifluoperazine. Coconut oil lavage is in several Indian protocols but evidence is weak. Mortality remains 60 to 80 percent. |
| Iron (ferrous sulphate overdose) | Desferrioxamine | 15 mg/kg/hour IV infusion. Stocked at tertiary centres; uncommon in adult Indian practice but a paediatric emergency. |
| Digoxin, oleander, Cerbera odollam | Digoxin-immune Fab fragments (Digifab, Digibind) | Effectively unavailable in Indian government supply; private metro hospitals stock a few vials. Most yellow oleander seed poisoning in southern India is managed with atropine, temporary pacing and supportive care. |
| Snake envenomation (Big Four: cobra, krait, Russell's viper, saw-scaled viper) | Polyvalent anti-snake venom (ASV) | Bharat Serums, VINS Bioproducts, Premium Serums. 10 vials IV initial dose, repeated at six-hour intervals based on clinical response and 20-minute whole blood clotting time. Universally stocked at CHC and above. |
| Scorpion sting (Mesobuthus tamulus) | Prazosin | 0.03 mg/kg orally every three to six hours until peripheries are warm. Indian protocol from KEM Mumbai and Mahatma Gandhi Institute of Medical Sciences Sevagram. Anti-scorpion serum is a second-line addition in Maharashtra and Gujarat protocols. |
The National Poisons Control Centre at AIIMS Delhi publishes the recommended antidote list for state and district pharmacies. The WHO essential medicines list defines a minimum stocking floor (atropine, naloxone, NAC, methylene blue, ASV, calcium gluconate for hydrofluoric acid). Implementation varies by state. Punjab and Kerala stock close to the recommended list at district hospitals; several northeastern states and parts of Bihar and Madhya Pradesh fall short, particularly on pralidoxime continuity.
The reasons for these gaps are operational rather than scientific. Pralidoxime ampoules have a short shelf life relative to atropine and need cold storage. Polyvalent ASV needs strict cold chain. Hydroxocobalamin in the Cyanokit format is expensive and is ordered only against forecasted demand, which is low in most district hospitals. Digoxin-Fab fragments are imported and priced beyond the reach of most public formularies. The result is a patchy national antidote map where the toxidrome can be recognised correctly and the antidote still be unavailable. The NPCC at AIIMS Delhi, and to a lesser extent the NPIC at Madras Medical College, do informal redistribution and referral coordination across this map; the helpline numbers are worth keeping in every emergency department contacts file.
The 20-minute whole blood clotting time (WBCT) deserves a separate mention. A clean glass test tube, 2 ml of venous blood, left undisturbed for 20 minutes and then tilted. If it has not clotted, the patient has consumption coagulopathy from a viper bite and ASV is indicated even without obvious local signs. The test costs nothing, needs no laboratory, and is the workhorse triage tool in rural Indian snakebite care.
A short note on paediatric poisoning closes this section. Children present with a narrower set of agents (paraffin and kerosene ingestion, household cleaners, iron tablets, accidental adult medication exposure, agricultural products in farming households) and a wider therapeutic margin of error. Indian paediatric protocols (Indian Academy of Paediatrics) keep iron poisoning, hydrocarbon aspiration and accidental alprazolam ingestion at the top of the differential. The toxidrome examination is the same; the doses scale by weight; the threshold to admit and observe is lower.