Adverse drug reaction Study Guide

📖 Core Concepts Adverse Drug Reaction (ADR) – An unintended medical event that is causally linked to a medication (can be harmful or beneficial). Adverse Event – Any unexpected occurrence during drug use, regardless of causality. Side Effect – A reaction proven to be related to the drug through thorough investigation. Pharmacovigilance – The science of detecting, assessing, and preventing ADRs. Serious vs. Severe Serious = outcome‑based (death, life‑threatening, hospitalization, disability, congenital anomaly, or intervention to prevent permanent damage). Severe = intensity of the clinical manifestation; not automatically serious. Traditional ADR Types (A–F) A: Augmented, dose‑dependent, predictable. B: Bizarre, idiosyncratic, dose‑independent, unpredictable. C: Chronic (long‑term use). D: Delayed (appears after drug stopped). E: Withdrawal (after discontinuation). DoTS Classification – Categorizes ADRs by Time‑relatedness, Dose‑relatedness, and Susceptibility (e.g., genetic factors). Pharmacogenomics – Study of how genetic variants (e.g., CYP450, N‑acetyltransferase) affect drug metabolism and ADR risk. Drug Interaction Types Additive – Same toxic mechanism (e.g., two QT‑prolonging drugs). Altered Metabolism – One drug inhibits/induces enzymes or transporters, changing another drug’s level. Causality Assessment – Determines how likely a drug caused an ADR (Naranjo, Venulet, WHO criteria; “certain” requires challenge‑dechallenge‑rechallenge). Medication‑Related Harm Beyond Reactions – Includes non‑adherence‑related problems. 📌 Must Remember FDA serious ADR criteria: death, life‑threatening, hospitalization, disability, congenital anomaly, or required intervention. Type A = predictable, dose‑dependent; Type B = unpredictable, idiosyncratic. Serious ≠ Severe – always check the outcome, not just intensity. Naranjo algorithm scores (≥9 = definite, 5‑8 = probable, 1‑4 = possible, ≤0 = doubtful). Challenge‑Dechallenge‑Rechallenge = gold standard for “certain” causality. Common in‑hospital ADR culprits (2011): steroids, antibiotics, opiates/narcotics, anticoagulants. Genetic polymorphisms in Phase I (CYP450) and Phase II (N‑acetyltransferase) enzymes can dramatically alter drug clearance. Additive QT‑prolongation → high risk of torsades; serotonergic polypharmacy → serotonin syndrome. 🔄 Key Processes Assessing ADR Causality Gather timeline, dose, concomitant meds, patient factors. Apply a structured tool (e.g., Naranjo): answer each question, total score → category. If possible, perform challenge‑dechallenge‑rechallenge to confirm “certain”. Classifying an ADR (A–F vs DoTS) Determine dose‑dependency → A (yes) or B (no). Evaluate time course: immediate, chronic, delayed, withdrawal → C/D/E. For DoTS, note: Time (onset vs cessation), Dose (dose‑related, dose‑independent), Susceptibility (genetics, disease, age). Reporting a Serious ADR Confirm seriousness criteria. Complete regulatory report (e.g., FDA MedWatch) within required timeframe. 🔍 Key Comparisons Type A vs. Type B Predictability: A = predictable; B = unpredictable. Dose‑dependence: A = dose‑dependent; B = dose‑independent. Serious vs. Severe Serious: outcome‑oriented (hospitalization, death, etc.). Severe: intensity of symptoms (e.g., mild rash vs. severe Stevens‑Johnson). Adverse Event vs. ADR vs. Side Effect Event: any untoward occurrence, causality unknown. ADR: event with proven or suspected causal link. Side Effect: verified drug‑related reaction (often predictable). Additive Interaction vs. Metabolic Interaction Additive: same toxic pathway → summed effect. Metabolic: one drug changes another’s concentration via enzyme induction/inhibition. ⚠️ Common Misunderstandings “Severe” automatically means “serious.” → Not true; severe rash may be mild in outcome. All side effects are ADRs. → Side effects are proven ADRs; some reactions remain “adverse events” until causality is shown. Only dose‑dependent reactions are important. → Type B idiosyncratic reactions can be life‑threatening. Non‑adherence is not an ADR. → It is a form of medication‑related harm and part of pharmacovigilance scope. Genetic testing eliminates ADR risk. → It reduces risk but does not guarantee safety; environmental factors still matter. 🧠 Mental Models / Intuition “Predictability Ladder” – Place ADRs on a ladder: A (bottom, predictable) → B (top, surprise); helps recall dose‑dependence. “Outcome Filter” – When you hear “serious,” instantly filter for death, hospitalization, disability, congenital defect, or required intervention. “Two‑Drug Interaction Map” – Visualize two drugs: overlapping toxic mechanisms = additive; one sits on top of the other’s metabolism = metabolic interaction. “Genetic Susceptibility Lens” – Picture each patient as a lens colored by CYP450 or Phase II variants; the same dose can look very different through different lenses. 🚩 Exceptions & Edge Cases Type D (Delayed) – Reaction appears after drug discontinuation (e.g., drug‑induced lupus). Type E (Withdrawal) – Symptoms emerge after stopping a drug (e.g., opioid withdrawal). Renal/Hepatic Insufficiency – Even a “Type A” drug can become “Type B‑like” due to accumulation. Polypharmacy in the Elderly – Multiple low‑dose drugs may produce additive toxicity despite each being within therapeutic range. Non‑adherence‑related Harm – Skipping doses can cause rebound hypertension, seizures, or therapeutic failure, classified as medication‑related harm. 📍 When to Use Which Classify ADR Use A–F when dose‑relationship and time course are clear. Use DoTS when you need a more granular view (e.g., suspect genetic susceptibility). Causality Tool Naranjo – When a structured numeric score is required (clinical trials, reports). WHO criteria – Quick bedside assessment when time is limited. Venulet – Research settings focusing on detailed chronology. Interaction Assessment Look for shared toxic mechanisms → consider additive risk (QT prolongation, serotonin syndrome). Identify enzyme inducers/inhibitors → evaluate metabolic interaction (dose adjustments, monitoring). 👀 Patterns to Recognize QT‑prolongation combo → multiple agents → high torsades risk. Serotonergic polypharmacy → MAOI + SSRI/TCAs → serotonin syndrome signs (hyperthermia, clonus). Renal failure + renally cleared drug → rising plasma levels → dose‑related ADRs. CYP450 poor metabolizer + standard dose → unexpected toxicity. Onset after drug discontinuation → suspect Type D delayed reaction. 🗂️ Exam Traps Choosing “severe” instead of “serious.” Exam may list “severe rash” as a serious outcome – it isn’t unless it leads to hospitalization. Labeling any side effect as an ADR. Only those with proven causality qualify. Assuming all ADRs are dose‑dependent. Type B reactions are classic counter‑examples. Mix‑up between additive and metabolic interactions. Additive = same toxic pathway; metabolic = enzyme effect. Overlooking non‑adherence as medication‑related harm. Questions may ask for sources of drug‑related injury; non‑adherence is a valid answer. Misidentifying Type C vs. Type D. Chronic (C) occurs during ongoing therapy; delayed (D) appears after stopping the drug. --- If any heading appears to lack source material, it has been omitted per instruction.