Practice with national-level exam (FACT, FACT Plus, NET, CUET, etc.) mocks, learn from structured notes, and get your doubts solved in one place.
How dose, route, age, sex, body mass, tolerance, idiosyncrasy, form, food, hepatic and renal status shift a poison from therapeutic to lethal in Indian forensic practice.
A poison is rarely a single, fixed quantity that produces a single, fixed outcome. The same 3 grams of aluminium phosphide kills a 22-year-old labourer in Bathinda within four hours and leaves a 45-year-old farmer in Sangrur alive after eighteen, despite both reaching the hospital at the same interval. The same 200 mL of locally brewed liquor blinds one drinker in a Saran district hooch lot and only mildly sickens his neighbour from the same bottle. The variables that make these outcomes diverge are the subject of this topic. Each one shifts the curve that maps dose to response, and each one is recorded somewhere in the post-mortem file because the defence at trial will probe it.
The page is the working companion to Classification of Poisons by Origin, Action and Chemical Nature and feeds the next page on signs, symptoms and antidotes. The framing is operational, not abstract: dose, route, age, sex, body mass, tolerance, idiosyncrasy, physical form, simultaneous food and alcohol, hepatic and renal status, drug-drug interactions, and finally how all of these change the post-mortem interpretation. The Indian anchor cases are real and from the published medico-legal record.
"The dose makes the poison." Paracelsus, five centuries old and still the first answer in every viva.
Dose is the variable that every other factor modifies. The classical statement is from Paracelsus in the sixteenth century: every substance is a poison; only the dose distinguishes a remedy from a toxin. Pure water in litres taken over an hour produces fatal hyponatraemic encephalopathy. Iron in milligrams is a haematinic; iron in grams kills a toddler who has rummaged through a parent's antenatal supplement bottle. The forensic toxicologist's first calculation on any case is dose in mg per kg body weight against the published lethal range for the agent.
The LD50 is the standard comparator. Established originally in animal studies and extrapolated to humans through allometric scaling, the LD50 lets a working analyst rank one poison against another on an objective scale. A short Indian medico-legal sample:
| Agent | Approximate human lethal dose | Notes |
|---|---|---|
| Cyanide (potassium) | ~3 to 5 mg/kg orally | Death within minutes by cytochrome c oxidase block; lower if dissolved in acidic stomach contents |
| Strychnine | 1 to 2 mg/kg | Convulsant alkaloid from nux vomica; classical case-study agent in Indian toxicology |
| Aluminium phosphide | 1.5 to 3 g of the 3 g tablet (one to two tablets) | Liberates phosphine in stomach acid; Punjab and Haryana epidemic agent |
| Paracetamol |
Five routes, five onset profiles, five different post-mortem patterns.
Route changes the speed of onset and the proportion of dose that reaches systemic circulation. The classical hierarchy for speed, from fastest to slowest, is intravenous, inhalation, intramuscular, subcutaneous, oral, dermal. The differences are not academic. A nicotine intoxication from a transdermal cessation patch (slow, steady, sub-toxic) and an acute nicotine toxicity from chewed gutka swallowed by a toddler (fast, peaked, fatal) involve the same molecule and very different timelines.
| Route | Typical onset | Bioavailability | Forensic relevance |
|---|---|---|---|
| Intravenous | Seconds | 100% | Heroin overdose with needle in situ, iatrogenic deaths, contaminated injections |
| Inhalation | Seconds to minutes | Near 100% for gases | CO in fires, phosphine after AlP, paint thinner and adhesive abuse, anaesthetic gas deaths |
| Intramuscular | 10 to 30 minutes | 75 to 100% | Snakebite envenomation site, depot antipsychotics, iatrogenic injections |
| Oral | 20 minutes to 2 hours |
The same dose, four different bodies. Four different outcomes.
Host factors shift the dose-response curve at the patient end. Age is the most powerful of these.
Paediatric. Infants and toddlers handle poisons very differently from adults. Hepatic enzyme systems are immature in the first six months (CYP3A4 and CYP2D6 are at adult capacity only by age one to two). The kidney clears slower in the neonate. The blood-brain barrier is more permeable. The body surface area to mass ratio is high, so dermal absorption is proportionally greater. Three Indian paediatric anchors are clinically routine: kerosene aspiration from a recapped soft-drink bottle is a hospital admission in every monsoon, with chemical pneumonitis the main injury; codeine cough syrup in an ultra-rapid CYP2D6 metaboliser child can cause fatal respiratory depression, a phenomenon documented in the South Indian paediatric literature; and paracetamol overdose in toddlers shifts to a sulphation-dominant clearance pathway, which is protective up to a point and then sharply pathological once the sulphation route is saturated.
Geriatric. Polypharmacy is the dominant variable in older patients. The average Indian patient over 65 in tertiary care is on five to nine medications, with predictable interactions. CYP activity falls with age, glomerular filtration declines, and acute kidney injury after NSAID exposure or aminoglycoside dosing is a routine finding. A diazepam dose that produces light sedation in a 30-year-old can produce 24-hour coma in an 80-year-old with hepatic and renal slowing.
Sex. Women metabolise ethanol more slowly than men of the same weight. The biochemical basis is two-fold: lower gastric and hepatic alcohol dehydrogenase activity, and a higher body fat percentage that gives a smaller water compartment for the ethanol to distribute into. A 60 kg woman and a 60 kg man drinking the same volume reach different peak blood ethanol concentrations, with the woman 15 to 25% higher. Pregnancy brings its own complications: physiological changes in gastric emptying, hepatic blood flow, renal clearance and plasma volume all shift drug handling, and the foetal compartment is a separate pharmacokinetic space with placental transfer of lipid-soluble agents.
Body mass and fat. Lipophilic drugs (THC, the benzodiazepines, fluoxetine) distribute into adipose tissue. An obese patient has a larger volume of distribution for these molecules, so plasma concentration after a given dose is lower, but the body burden is higher and the elimination half-life is longer. The post-mortem implication is that adipose tissue can serve as a slow-release depot from which lipophilic drugs leach into blood after death, complicating the interpretation of post-mortem blood concentration.
Same dose, same body, opposite outcome. The genome is the explanation.
Tolerance is the acquired side of individual variation. A naive adult given 30 mg of oral morphine experiences sedation and analgesia, perhaps mild respiratory depression. A long-term opioid user maintained on 200 mg morphine equivalent per day takes 100 mg as a routine dose with no respiratory compromise. The mechanism is pharmacodynamic, primarily mu-opioid receptor downregulation and intracellular adaptation. A chronic alcoholic in Delhi tertiary care can be admitted with a blood ethanol of 380 to 420 mg/dL while still conversational, walking and oriented, a level that would respiratory-arrest a naive drinker. Mithridatism, named for Mithridates VI of Pontus, is the inducible-tolerance idea taken to its logical extreme: gradual escalating doses to render the body resistant to a known poison.
The forensic catch is the tolerance reset on withdrawal. An opioid user discharged from a deaddiction centre or released from prison loses tolerance over days to weeks; a relapse dose calibrated to the previous tolerance level becomes a fatal overdose. The post-relapse overdose death is the dominant pattern in Indian opioid mortality and is documented in NDPS deaddiction follow-up cohorts in Punjab and Manipur.
Idiosyncrasy is the inherited side. It looks like an abnormal response, but the underlying mechanism is genetic polymorphism in the enzymes that handle the drug.
| Polymorphism | Drug affected | Phenotype | Indian relevance |
|---|---|---|---|
| G6PD deficiency | Primaquine, dapsone, sulphonamides, naphthalene | Haemolytic anaemia on exposure | Prevalence 5 to 27% in some Indian populations; routine pre-treatment screening before primaquine |
The same molecule in a different packaging is a different poison.
The physical state and formulation of a poison change its toxicity at the absorption end. Solid metallic arsenic is poorly absorbed from the gut; arsenic trioxide dissolved in tea is absorbed efficiently and is a classical homicidal vehicle. A swallowed gas does not exist as a swallowed gas; it exists as the residue of a tablet (aluminium phosphide), or a liquid (mercury), or dissolved acid (formic acid in formic acid swallowing). Micronised drug particles in a modern formulation reach peak concentration faster than the same drug in a crystalline tablet. Sustained-release formulations spread the same dose over 12 to 24 hours and produce a different toxidrome from immediate-release of the same molecule. The post-mortem investigator looks for the original formulation because the formulation reads the timing of intake.
Food and alcohol modify oral absorption in ways that change the lethal threshold.
Hepatic and renal status shifts elimination. Cirrhosis prolongs the half-life of benzodiazepines, paracetamol metabolites, opioids and most CYP-cleared drugs. Renal impairment delays clearance of digoxin, lithium, metformin, aminoglycosides and most water-soluble compounds. A 70-year-old with stage 3 CKD takes the same digoxin dose as a healthy adult and arrives in emergency with toxic levels and a high-degree AV block two weeks later.
Drug-drug interactions sit on top of all of this. Warfarin metabolism is shifted by dozens of co-administered drugs through CYP2C9 induction and inhibition; the medico-legal warfarin case requires a full medication history. An SSRI co-administered with tramadol, linezolid, MDMA or pethidine can precipitate serotonin syndrome at therapeutic doses of each.
How the eleven factors collapse a 'lethal' concentration into a 'therapeutic' one, and back.
The forensic toxicologist's report does not simply state a blood concentration and a textbook lethal range. It compares the measured concentration against a patient-specific lethal range that has been adjusted for the factors in this page. The adjustment is not arbitrary; it is a structured walk-through.
A 60 kg chronic opioid user maintained on 240 mg oral morphine equivalent per day takes an additional 100 mg of oral morphine. The expected outcome is best described as:
| Hepatotoxic from >150 mg/kg single dose |
| Therapeutic window narrows with alcohol, fasting and CYP2E1 induction |
| Organophosphate (monocrotophos) | Lethal at ~100 to 200 mg orally for an adult | Cholinergic crisis; the dominant rural poison south of the Vindhyas |
| Datura seed | 15 to 25 seeds approximately | Anticholinergic toxidrome; the Datura kheer railway robberies |
The numbers are point estimates from population averages. Every other factor in this page shifts them. A chronic opioid user can survive a single oral dose of 200 mg of morphine that would respiratory-arrest a naive adult. A G6PD-deficient patient can develop haemolytic crisis from a primaquine dose that another patient swallows without symptom. The toxicologist who quotes a lethal dose at trial without qualifying it for individual variation is open to a defence cross-examination that will run for an hour.
| Highly variable (first-pass) |
| The default route for suicidal and homicidal poisoning in India |
| Dermal | Minutes to hours | Low to moderate | Organophosphate skin contamination in farmworkers, transdermal therapeutic systems |
Intravenous delivery bypasses every barrier. The full dose reaches the central compartment in one circulation time, which is roughly 30 seconds. Inhalation is almost as fast for gases and aerosolised particles because the alveolar surface is large and the diffusion path is short. Carbon monoxide in a closed garage reaches lethal carboxyhaemoglobin levels in minutes; phosphine liberated from an aluminium phosphide tablet in the stomach reaches lethal blood concentrations after a short oral absorption phase, which is why AlP looks like an inhalation poison even though the tablet is swallowed.
Oral dosing introduces the longest set of intervening variables: gastric pH, gastric emptying, intestinal motility, gut-wall enzymes (CYP3A4 in the enterocyte), portal circulation and first-pass hepatic metabolism. A drug with high first-pass extraction, like morphine, has perhaps 30% oral bioavailability against 100% intravenous, which is why oral morphine doses are roughly three times the intravenous equivalent. A homicidal poisoner who knows the route effect can choose the molecule accordingly; an investigating officer who finds an empty injection vial at a scene reads the post-mortem differently from one who finds an empty pill blister.
Dermal absorption is slow but real for lipid-soluble compounds. Organophosphate splash on the forearm of a farmworker spraying without gloves produces a slow-building cholinergic syndrome over hours, very different from the rapid toxidrome of an ingested dose. The post-mortem interpretation includes skin contamination patterns, clothing residue and the absence of a meaningful gastric residue in dermal cases.
| CYP2D6 ultra-rapid metaboliser | Codeine, tramadol | Excessive conversion to morphine; respiratory depression | Documented in South Asian populations; codeine restricted in paediatric use |
| CYP2D6 poor metaboliser | Codeine, tramadol | Inadequate analgesia from prodrugs; high parent-drug levels of beta-blockers, tricyclics | Around 1 to 2% of Indian population |
| CYP2C19 poor metaboliser | Clopidogrel, omeprazole, diazepam | Reduced activation of clopidogrel; prolonged diazepam half-life | 10 to 20% of Indians; relevant in cardiology and toxicology |
| NAT2 slow acetylator | Isoniazid, hydralazine, sulphonamides | INH hepatotoxicity, drug-induced lupus, sulphonamide reactions | Around 60% of North Indians are slow acetylators; explains TB programme hepatotoxicity rates |
The Indian Council of Medical Research and the Indian Genome Variation Consortium have published frequency data for several of these polymorphisms across Indian regional populations. NAT2 slow acetylator status in particular drives the high rates of isoniazid hepatotoxicity seen in the RNTCP programme. Forensic interpretation of an INH overdose or an unexpected hepatic reaction at therapeutic dose has to consider acetylator status, especially when the medico-legal record shows a programme-supplied dose schedule and an unexpectedly severe clinical course.
The Bihar hooch tragedies of recent years are a working case study for how these factors play out at scale. A batch of methanol-contaminated illicit liquor distributed across a cluster of villages produces a wide outcome spread: some drinkers die within 24 hours, some go blind from optic nerve infarction, some recover with no permanent injury. The published epidemiology points to dose per drinker (volume consumed), simultaneous ethanol intake (ethanol competitively inhibits alcohol dehydrogenase and so slows formate production from methanol, which is the basis of ethanol therapy for methanol poisoning), gastric content, age and underlying nutritional state including folate status, and individual variation in formate dehydrogenase activity. The same poison, the same batch, eleven different host environments, eleven different outcomes.
ICMR pharmacogenomic mapping in Indian regional populations now informs paediatric prescribing guidelines, particularly for codeine and tramadol. The trajectory is toward case-by-case toxicology that reads the patient's genome alongside the analytical result. For the working post-mortem report in 2026, the factors in this page remain the structured checklist that converts a raw concentration into a forensic interpretation.