Toxicology and Adverse Drug Reactions
Toxicology and Adverse Drug Reactions tests risk assessment after overdose or drug exposure, recognition of toxidromes, appropriate decontamination, antidote use, and ADR classification. The exam rewards time-critical reasoning and avoids unnecessary interventions.
Core rules
- History includes substance, dose, time, co-ingestants, symptoms, and patient weight.
- Toxidromes guide early resuscitation: opioid, anticholinergic, cholinergic, sympathomimetic, and sedative-hypnotic patterns.
- Activated charcoal is most useful early after a significant ingestion and is not routine for every overdose.
- Antidotes are specific: naloxone for opioids, N-acetylcysteine for paracetamol, flumazenil only in selected cases.
- ADRs are classified by mechanism and timing; causality tools such as Naranjo structure, but do not replace clinical judgment.
Worked example
A 60 kg adult ingests 15 g of paracetamol 4 hours ago. The acute toxic threshold is about 150 mg/kg, which is 60 x 150 = 9000 mg, or 9 g. The ingestion exceeds that threshold. Obtain a serum paracetamol level at least 4 hours after ingestion and compare it with the treatment nomogram; if the level is above the treatment line or unavailable with a significant ingestion, start N-acetylcysteine. The reasoning combines weight-based threshold, timing, and nomogram rather than waiting for symptoms.
Traps
Do not induce vomiting. Do not give charcoal hours later without considering airway risk and benefit. Do not wait for liver enzymes to rise before treating paracetamol toxicity. Do not use flumazenil routinely in mixed overdose or seizure risk. Do not label every adverse event as an ADR without assessing timing and alternative causes.