Factors Affecting the Intensity of Poisoning

Dose describes an amount administered or encountered, often related to body mass for a specified purpose. Exposure concentration and duration may be more informative for an inhaled agent. Neither term is interchangeable with the concentration measured in a biological specimen after the event.

LD50 is the dose associated with death in half of a defined experimental population under stated conditions. Species, route, formulation and observation period affect the result. It is not a human patient-specific lethal dose. Comparing agents using LD50 values from incompatible studies can be misleading.

A graded response concerns the magnitude of an effect, such as a change in an enzyme measurement. A quantal response concerns the proportion of a population meeting a specified endpoint. A population curve does not show that everyone below a particular dose is safe or everyone above it will die.

Clinical assessment thresholds have a different purpose from experimental toxicity values. For example, an acetaminophen assessment may require the timing and pattern of ingestion, a timed blood result and the relevant clinical pathway. A single-dose threshold must not be repurposed for repeated, staggered or unknown-time exposure, or used as a forensic fatal-dose rule.

For a numerical comparison, suppose a hypothetical reported exposure is 100 mg in a person weighing 50 kg. The nominal amount is 2 mg/kg. The arithmetic is straightforward, but it does not show how much was absorbed, whether the report was accurate or what outcome should follow. Those limits must accompany the number.

The schematic also shows ED50, the median dose for a specified effect, and TD50, the median dose for a defined toxic effect. A therapeutic index may be expressed as TD50/ED50 under compatible conditions. An experimental LD50/ED50 ratio is another historical formulation. The endpoint must always be named; these ratios are not personal dosing instructions.

For example, if hypothetical study values are ED50 = 2 units and TD50 = 20 units for the same population and route, the ratio is 10. This compares median endpoints, not the full overlap between the response distributions. A patient may experience toxicity below a population median, and different adverse effects can have different dose-response relationships.

Intravenous administration places a substance directly into the circulation and has complete systemic availability by definition. Other routes involve barriers whose importance depends on the agent, formulation and physiology. An injection into muscle or tissue is not equivalent to an intravenous dose; animal envenomation is not reliably described as a standard intramuscular injection.

Oral exposure involves dissolution, gastrointestinal transit, absorption and potentially substantial intestinal or hepatic first-pass metabolism. Vomiting, altered gastric emptying, modified-release formulations and co-ingested substances can change the concentration-time profile. A tablet found at autopsy is evidence of material present, not a clock that uniquely dates ingestion.

Inhaled gases and vapours can act rapidly, but uptake depends on concentration, duration, ventilation, solubility and pulmonary exchange. Near-complete absorption should not be assigned to every gas. Some agents also injure the airway or lungs directly, and delayed injury can occur.

Dermal exposure depends on the chemical, vehicle, contact area, duration and skin condition. Contaminated clothing may prolong contact. Transdermal medicines are designed for controlled delivery, whereas a spill may create very different exposure conditions. An intact patch does not prove the delivered dose.

Scene findings can support a route hypothesis: injection equipment, skin contamination, a patch, a damaged container or gastric material. Each finding needs independent assessment. Do not infer that absent gastric residue excludes ingestion, or use a generic oral-to-intravenous ratio to reconstruct a fatal exposure.

Age changes physiology, but not through a single switch. The development of metabolism and renal function in infants is pathway-specific. Children are not scaled-down adults, and body size, formulation, behaviour and access to products can affect exposure. Avoid assigning all hepatic enzymes one maturity age.

Older people may have altered renal function, different body composition, multiple illnesses and interacting medicines. Chronological age alone does not predict clearance or severity. Use actual clinical information where available, including relevant laboratory results and the medication record.

For alcohol, total body water helps explain why the same intake can produce different concentrations. On average, women have less body water than men of similar weight, but individuals vary. This population observation does not justify a fixed percentage adjustment for every person or a universal claim about their elimination rate.

Body mass can affect the dose expressed per kilogram. Body composition, protein binding and tissue affinity can affect distribution. However, obesity does not always produce lower blood concentrations or longer half-lives, and body fat does not provide a universal explanation for post-mortem redistribution. Use substance-specific pharmacokinetic evidence.

Pregnancy may alter distribution and elimination and can introduce fetal exposure through placental transfer. The magnitude and clinical importance depend on the agent and stage of pregnancy. A general statement about pregnancy cannot substitute for the relevant clinical and toxicological evidence.

The forensic task is to record which factors are known, which are plausible and which remain unmeasured. Nationality, occupation or a population-average characteristic should not be substituted for evidence about the individual.

Tolerance is a reduced response after repeated exposure. It may involve pharmacodynamic adaptation, altered disposition or learned compensation, depending on the substance and effect. Tolerance to one effect need not match tolerance to another, and cross-tolerance between substances may be incomplete.

Opioid tolerance does not guarantee protection from respiratory depression. High doses, co-use of alcohol or sedatives, illness and interruptions in use can increase risk. It is scientifically inappropriate to predict that an additional opioid dose will produce only mild sedation from a reported maintenance dose. Such an example is not a safe dosing recommendation.

Tolerance can diminish after a period without the substance. Returning to a previously used amount may then carry increased overdose risk. The rate and extent of change vary, so a fixed abstinence period cannot establish an individual's current tolerance from the case record alone.

Idiosyncratic adverse reactions are unusual individual responses and are not all explained by a known inherited enzyme variant. Pharmacogenetics addresses defined genetic influences on drug response, but genotype does not by itself establish the cause of an adverse event.

Codeine and tramadol illustrate why the exact pathway matters. CYP2D6 contributes to the formation of morphine from codeine and O-desmethyltramadol from tramadol. Calling both products morphine is incorrect. Parent and metabolite concentrations are also affected by timing, other pathways, treatment and specimen conditions.

A specialist pharmacogenetic investigation may help an unusual case when justified. Interpret it with the clinical course and analytical findings. A person's country of origin does not establish their metabolic phenotype; individual testing and relevant clinical evidence are more informative.

Formulation can change the rate and extent of absorption. Immediate-release and modified-release products may produce different concentration-time profiles, and mixed products can contain more than one active ingredient. Particle size, solubility and the chemical form also matter, but no single rule applies to every compound.

Food may delay, increase or reduce absorption depending on the substance and formulation. It does not universally protect against poisoning or speed every lipophilic agent into circulation. Use product-specific or experimentally supported information, and distinguish a possible mechanism from a demonstrated effect in the case.

Alcohol interactions can involve both disposition and combined physiological effects. Alcohol with opioids or sedatives can increase respiratory-depression risk. With acetaminophen, chronic heavy drinking, nutrition, timing and the pattern of acetaminophen use require consideration. A claim that every chronic drinker develops liver failure at a particular daily amount is not justified.

Acetaminophen can form the reactive metabolite NAPQI; depletion of protective glutathione contributes to injury in overdose. Repeated supratherapeutic use, fasting, malnutrition and underlying illness can complicate assessment. Acute co-ingestion of alcohol and chronic alcohol use are not interchangeable histories, and neither permits an automatic forensic correction to a lethal dose.

Renal impairment can reduce elimination of medicines or active metabolites that depend on renal clearance. Hepatic disease can affect metabolism, protein binding and blood flow. The direction and magnitude are drug-specific: the phrase liver disease does not mean every drug has the same increase in half-life.

Drug interactions can involve enzyme inhibition or induction, altered renal handling, protein binding or additive effects at a target. A full medication and treatment history is therefore essential. An interaction may explain a finding without proving medication error or deliberate overdose.

Post-mortem toxicology adds uncertainty that is separate from the variation during life. Some drugs redistribute between tissues and blood after death, and results can differ by sampling site and interval. Decomposition, instability and microbial activity can create further complications.

Peripheral blood is often preferred for interpretation, but it is not an unchanged sample of the concentration at the moment of death. Identify its anatomical source and collection details, and assess the substance-specific evidence. There is no universal central-to-peripheral correction that reconstructs the antemortem value.

Reference concentration ranges can overlap between treated patients, impaired individuals and fatal cases. Tolerance, co-exposures, specimen differences and case selection help explain that overlap. A result should be compared only with appropriate reference information, with its limitations stated.

A useful interpretive sequence is to confirm the analytical result, assess specimen and timing limits, review exposure and treatment evidence, consider host factors, and compare plausible explanations. Where information is unavailable, identify the resulting limit rather than replacing it with a presumed national pattern.

The final opinion can explain that a finding is compatible with a particular exposure or may have contributed to effects. Stronger causal claims require sufficient supporting evidence. Different outcomes after reportedly similar exposure do not establish a personalised dose-response equation.

Drug disposition is developed in Drug Metabolism, Distribution and Metabolite Identification.

Post-mortem sampling is developed in Post-Mortem Examination and Viscera Collection in Poisoning.