Fiche de révision : Understanding Adverse Drug Reactions and Susceptibility

📋 Course Outline

1. Adverse Drug Reactions & Definitions
2. ADR & Pharmacological Mechanism
3. Side Effects & Pharmacological Properties
4. ADR & Adverse Drug Event
5. Epidemiology & Incidence
6. Classification & ADR Types
7. Factors & Susceptibility
8. Genetics & Drug Response
9. Immunological & Allergic Reactions
10. Causality & Assessment Methods

📖 1. Adverse Drug Reactions & Definitions

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for prophylaxis, diagnosis, or therapy, without needing to prove a pharmacological mechanism (WHO definition).
• Side Effect: An unintended effect related to a drug's pharmacological properties, which can sometimes be beneficial or neutral, distinct from ADR.
• Adverse Drug Event (ADE): An adverse outcome after drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not all ADEs are ADRs.
• Types of ADRs (Rawlins-Thompson Classification):
  • Type A: Predictable, dose-dependent, common, and preventable (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, not dose-dependent, often serious (e.g., allergic reactions).
  • Type C: Dose and time-related, related to cumulative dose (e.g., adrenal suppression by corticosteroids).
  • Type D: Delayed effects, occurring some time after drug use (e.g., carcinogenesis).
  • Type E: Occur after withdrawal of the drug (e.g., opiate withdrawal).
  • Type F: Unexpected failure of therapy, often due to interactions (e.g., contraceptive failure with enzyme inducers).

📝 Essential Points

• Distinction from Toxicity: ADRs occur during normal dosing, whereas toxicity often results from overdose or poisoning.

• Causality: Establishing a causal link between drug and adverse effect is crucial; tools like the Naranjo algorithm assist in causality assessment.

• Epidemiology: ADRs account for 2.6%-6.5% of hospital admissions, with 3.5%-14.7% of inpatients affected, and are a leading cause of death (4th-6th in the USA).

• Factors Influencing Susceptibility:

  • Age: Elderly and children are more vulnerable due to metabolic and physiological differences.
  • Gender: Women may experience certain ADRs more frequently (e.g., torsade de pointes).
  • Co-morbidities & Polypharmacy: Impaired organ function and multiple drugs increase ADR risk.
  • Ethnicity: Genetic traits influence drug metabolism and ADR susceptibility.
  • Pharmacogenetics: Variations in genes affect drug response and metabolism, enabling personalized medicine.

• Immunological Reactions: Allergic responses involve immune recognition of drugs as foreign, leading to reactions like rashes, serum sickness, or anaphylaxis, often requiring prior exposure.

• Prevention Strategies:

  • Review previous ADR history.
  • Rational drug selection and dosing.
  • Monitoring therapy (e.g., serum levels, renal function).
  • Patient education on risks.

💡 Key Takeaway

Adverse drug reactions are unintended, potentially serious responses to medications that vary based on individual factors, and proactive identification, monitoring, and patient education are essential to minimize their occurrence and impact.

📖 2. ADR & Pharmacological Mechanism

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for prophylaxis, diagnosis, or therapy, without the need to prove a specific pharmacological mechanism.
• Side Effect: An unintended effect related to the drug's pharmacological properties, which may include beneficial or harmful outcomes, distinct from ADRs.
• Adverse Drug Event (ADE): An adverse outcome following drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not vice versa.
• Type A ADRs: Predictable, dose-dependent reactions resulting from exaggerated pharmacological effects; most common (~80%), preventable.
• Type B ADRs: Unpredictable, often immune-mediated or idiosyncratic reactions unrelated to dose or pharmacology; potentially severe and less common.
• Pharmacogenetics/Pharmacogenomics: The study of how genetic variations influence individual drug responses, enabling personalized medicine.

📝 Essential Points

• Mechanisms of ADRs: Include pharmacodynamic (response variability) and pharmacokinetic (absorption, metabolism, elimination) factors.
• Classification of ADRs:
  • Type A: Dose-dependent, predictable, common, low morbidity/mortality (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, immune-mediated or idiosyncratic, often severe (e.g., hepatotoxicity, allergic reactions).
  • Type C: Cumulative, related to dose/time (e.g., corticosteroid adrenal suppression).
  • Type D: Delayed effects (e.g., carcinogenesis).
  • Type E: Occur after withdrawal (e.g., opiate withdrawal).
  • Type F: Unexpected failure of therapy, often due to drug interactions (e.g., contraceptive failure with enzyme inducers).
• Factors influencing susceptibility: Age (elderly, children), gender, co-morbidities, ethnicity, genetics, immune status.
• Genetic influence: Variations in drug-metabolizing enzymes (e.g., acetylation, oxidation) and drug targets affect response and ADR risk.
• Immunological reactions: Allergic responses involve immune recognition of drugs as foreign, with types I-IV reactions, independent of pharmacological effects.
• Causality assessment: Tools like the Naranjo algorithm help determine the likelihood that a drug caused an ADR, based on clinical data.
• Prevention strategies: Include thorough patient history, rational prescribing, monitoring (renal function, blood counts), and patient education about risks.

💡 Key Takeaway

Understanding the mechanisms, classification, and risk factors of ADRs is essential for prevention, early detection, and personalized management, ultimately reducing patient harm and healthcare costs.

📖 3. Side Effects & Pharmacological Properties

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for therapy, prophylaxis, or diagnosis, without the need to prove a pharmacological mechanism.
• Side Effect: An unintended effect related to a drug's pharmacological properties, which can sometimes be beneficial or neutral.
• Adverse Drug Event (ADE): An adverse outcome following drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not vice versa.
• Pharmacogenetics: The study of how genetic differences influence individual responses to drugs.
• Pharmacogenomics: The broader study of how the entire genome affects drug response, leading to personalized medicine.
• Immunological Reactions: Allergic responses triggered by the immune system recognizing drugs as foreign, independent of pharmacological action.

📝 Essential Points

• Classification of ADRs (Rawlins-Thompson):

  • Type A: Predictable, dose-dependent, common, related to pharmacological effects (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, not dose-dependent, potentially serious (e.g., hepatotoxicity, allergic reactions).
  • Type C: Dose and time-related, related to cumulative dose (e.g., corticosteroid suppression).
  • Type D: Delayed effects, occurring some time after use (e.g., carcinogenesis).
  • Type E: Occur at end of drug use or withdrawal (e.g., opiate withdrawal).
  • Type F: Unexpected failure of therapy, often due to drug interactions (e.g., contraceptive failure with enzyme inducers).

• Factors Influencing Susceptibility:

  • Age: Elderly are more prone due to decreased metabolism and multiple medications; children have unique pharmacokinetics.
  • Gender: Women may have higher susceptibility to certain ADRs, such as torsade de pointes.
  • Co-morbidities & Concomitant Drugs: Impaired organ function and polypharmacy increase ADR risk.
  • Ethnicity: Genetic traits affect drug metabolism, e.g., increased angioedema risk with ACE inhibitors in Africans.
  • Genetics: Variations in genes affecting drug metabolism (e.g., acetylation, oxidation) and response (e.g., warfarin resistance).

• Immunological Reactions:

  • Can cause a range of allergic responses, from rashes to anaphylaxis.
  • Require prior exposure; immune recognition is independent of pharmacological effect.

• Causality Assessment:

  • Naranjo Algorithm: A questionnaire-based method to estimate the likelihood that a drug caused an adverse event, categorizing as highly probable, probable, possible, or doubtful.

• Prevention of ADRs:

  • Review patient history for previous ADRs.
  • Use risk stratification and tailored drug choices.
  • Rational prescribing and effective communication.
  • Monitoring therapy via physiological or serum markers.
  • Educating patients about potential risks and signs of ADRs.

• Serious ADRs:

  • Result in death, life-threatening situations, hospitalization, disability, or congenital anomalies.

• Severity & Prevalence:

  • Severity is classified from mild to severe based on activity limitation.
  • Prevalence ranges from very common (>10%) to rare (<0.1%).

💡 Key Takeaway

Understanding the pharmacological and immunological basis of side effects and ADRs, along with patient-specific factors, is essential for preventing, identifying, and managing adverse drug reactions effectively, thereby improving patient safety and therapeutic outcomes.

📖 4. ADR & Adverse Drug Event

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for prophylaxis, diagnosis, or therapy, without the need to prove a pharmacological mechanism. Defined by WHO as responses that are harmful and unexpected during typical use.

• Adverse Drug Event (ADE): An adverse outcome that occurs after drug use, which may or may not be causally linked to the drug. All ADRs are ADEs, but not all ADEs are ADRs.

• Side Effect: An unintended effect related to a drug’s pharmacological properties, which can sometimes be beneficial; distinct from ADR.

• Causality Assessment: The process of determining whether a drug caused an adverse effect, often using tools like the Naranjo algorithm to quantify the likelihood.

• Types of ADRs (Rawlins-Thompson Classification):

  • Type A: Predictable, dose-dependent, common, and preventable (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, not dose-dependent, often serious (e.g., allergic reactions).
  • Type C: Dose and time-related, related to cumulative dose.
  • Type D: Delayed effects appearing after some time (e.g., carcinogenesis).
  • Type E: Occur after withdrawal of the drug.
  • Type F: Unexpected failure of therapy, often due to interactions.

• Pharmacogenetics & Pharmacogenomics: Study of genetic factors influencing individual drug responses, leading to personalized medicine.

📝 Essential Points

• Epidemiology: ADRs account for 2.6-6.5% of hospital admissions, with 3.5-14.7% of inpatients affected; responsible for 2.3% of deaths. They prolong hospital stays (~20 days) and increase healthcare costs.

• Factors Influencing Susceptibility:

  • Age: Elderly patients are more prone due to decreased metabolism and multiple medications; children have unique physiological responses.
  • Gender: Women may experience more ADRs, especially related to QT prolongation and psychiatric effects.
  • Co-morbidities & Polypharmacy: Chronic diseases and multiple drugs increase risk due to altered pharmacokinetics and pharmacodynamics.
  • Ethnicity: Genetic traits affect drug metabolism and response, e.g., increased angioedema risk with ACE inhibitors in Africans.
  • Genetics: Variations in drug-metabolizing enzymes (e.g., acetylation, oxidation) influence individual responses and toxicity risk.

• Immunological Reactions: Allergic responses involve immune recognition of drugs as foreign, leading to reactions such as rashes, serum sickness, angioedema, or anaphylaxis. Prior exposure is often necessary.

• Prevention Strategies:

  • Review patient history for previous ADRs.
  • Rational drug selection and dosing.
  • Monitoring therapy via physiological or serum markers.
  • Patient education on risks.
  • Use causality assessment tools like the Naranjo algorithm.

• Serious ADRs: Result in death, life-threatening situations, hospitalization, disability, or congenital anomalies.

💡 Key Takeaway

Adverse drug reactions are common, often preventable, and influenced by multiple factors including genetics, age, gender, and co-morbidities. Effective prevention, monitoring, and patient education are essential to minimize their impact and improve patient safety.

📖 5. Epidemiology & Incidence

🔑 Key Concepts & Definitions

• **Adverse Drug Reaction (ADR):
  A noxious and unintended response to a drug occurring at normal doses used for treatment, prophylaxis, or diagnosis, without needing to prove a pharmacological mechanism.
• Adverse Drug Event (ADE):
  An adverse outcome after drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not all ADEs are ADRs.
• Incidence of ADRs:
  The frequency with which ADRs occur in different settings, such as hospital admissions (2.6%-6.5%), inpatients (3.5%-14.7%), and primary care (25%-30%).
• Classification of ADRs (Rawlins-Thompson):
  • Type A: Predictable, dose-dependent, common (~80%), low morbidity/mortality.
  • Type B: Unpredictable, immune-mediated or bizarre, serious, less common.
  • Type C: Dose and time-related, related to cumulative dose.
  • Type D: Delayed effects, occurring some time after drug use.
  • Type E: Occur at end of drug use, e.g., withdrawal syndromes.
  • Type F: Unexpected therapy failure, often due to interactions.

📝 Essential Points

• Epidemiology:
  ADRs account for 2.6%-6.5% of hospital admissions, with 3.5%-14.7% of inpatients affected, and cause approximately 2.3% of patient deaths. They extend hospital stays (~20 days vs. ~8 days), increasing costs.
• Risk Factors:
  • Age: Elderly and children are more susceptible due to metabolic and physiological differences.
  • Gender: Women may have higher susceptibility to certain ADRs, such as torsade de pointes.
  • Co-morbidities & Polypharmacy: Chronic diseases and multiple drugs increase ADR risk via pharmacokinetic and pharmacodynamic changes.
  • Ethnicity: Genetic traits influence drug metabolism, affecting ADR risk (e.g., increased angioedema in Africans on ACE inhibitors).
  • Genetics: Variations in drug-metabolizing enzymes (e.g., slow acetylators) and pharmacodynamics influence individual susceptibility.
• Immunological Reactions:
  Allergic responses involve immune recognition of drugs as foreign, leading to reactions ranging from rashes to anaphylaxis, requiring prior exposure.
• Prevention & Monitoring:
  • Check previous ADR history.
  • Rational drug selection and dosing.
  • Monitor therapy through physiological or serum markers.
  • Educate patients on risks to facilitate informed decisions.

💡 Key Takeaway

Understanding the epidemiology and risk factors of ADRs enables targeted prevention, early detection, and safer prescribing practices, ultimately reducing hospitalizations, costs, and mortality associated with adverse drug reactions.

📖 6. Classification & ADR Types

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for treatment, prophylaxis, or diagnosis, without the need to prove a pharmacological mechanism.
• Side Effect: An unintended effect related to a drug's pharmacological properties, which can sometimes be beneficial or neutral, distinct from ADRs.
• Adverse Drug Event (ADE): Any adverse outcome following drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not vice versa.
• Causality Assessment: The process of determining the likelihood that a drug caused an adverse reaction, often using tools like the Naranjo algorithm.
• Serious ADR: An adverse event resulting in death, life-threatening situation, hospitalization, disability, or congenital anomaly.
• Pharmacogenetics/Pharmacogenomics: Fields studying how genetic variability influences individual drug responses, enabling personalized medicine.

📝 Essential Points

• WHO Definition: Focuses on reactions that are noxious, unintended, and occur at normal doses, excluding toxicity from overdose or contamination.

• Types of ADRs (Rawlins-Thompson Classification):

  • Type A: Predictable, dose-dependent, common, and preventable (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, not dose-dependent, often serious (e.g., allergic reactions, hepatotoxicity).
  • Type C: Dose and time-related, related to cumulative dose (e.g., corticosteroid adrenal suppression).
  • Type D: Delayed effects, occurring some time after drug use (e.g., carcinogenesis).
  • Type E: Occur at end of drug use or withdrawal (e.g., opiate withdrawal).
  • Type F: Unexpected failure of therapy, often due to drug interactions (e.g., contraceptive failure with enzyme inducers).

• Factors Influencing Susceptibility:

  • Age: Elderly are more prone due to decreased metabolism and multiple medications; children have unique physiological responses.
  • Gender: Women may experience higher rates of certain ADRs (e.g., torsade de pointes).
  • Co-morbidities & Polypharmacy: Impaired organ function and drug interactions increase ADR risk.
  • Ethnicity: Genetic traits influence drug metabolism and ADR risk (e.g., increased angioedema in Africans).
  • Genetics: Variations in genes affecting drug metabolism and response (pharmacogenetics) can predispose to ADRs.

• Immunological Reactions: Allergic responses involve immune recognition of drugs as foreign, leading to reactions like rashes, anaphylaxis, or serum sickness, independent of pharmacological action.

• Prevention & Monitoring:

  • Review patient history for prior ADRs.
  • Tailor drug choices based on individual risk factors.
  • Use rational prescribing and shared decision-making.
  • Monitor therapy through physiological or laboratory markers (e.g., renal function, blood counts).
  • Educate patients about potential risks to enable informed consent.

💡 Key Takeaway

Adverse Drug Reactions are complex, multifactorial responses that can be classified into predictable or unpredictable types, with genetic, physiological, and immunological factors influencing individual susceptibility. Effective prevention hinges on careful assessment, monitoring, and patient education to minimize harm and optimize therapy.

📖 7. Factors & Susceptibility

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR):
  A noxious, unintended response to a drug occurring at normal doses used for prophylaxis, diagnosis, or therapy, without the need to prove a pharmacological mechanism.

• Adverse Drug Event (ADE):
  An adverse outcome after drug use, which may or may not be causally linked to the drug, unlike ADRs which require suspicion of causality.

• Type A (Augmented) ADRs:
  Predictable, dose-dependent reactions related to the pharmacological effects of the drug, accounting for 80% of ADRs. Example: Bradycardia from β-blockers.

• Type B (Bizarre) ADRs:
  Unpredictable, not dose-dependent, often immune-mediated or allergic, potentially severe or fatal. Example: Hepatotoxicity of isoniazid.

• Pharmacogenetics & Pharmacogenomics:
  The study of how genetic variability influences individual drug responses, leading to personalized medicine approaches.

• Susceptibility Factors:
  Patient-specific characteristics influencing ADR risk, including age, gender, co-morbidities, ethnicity, and genetic makeup.

📝 Essential Points

• Age:
  Elderly patients are more prone to ADRs due to decreased metabolism and elimination, and multiple co-morbidities. Children, especially neonates, have distinct physiological differences increasing their risk, such as immature blood-brain barriers and altered drug metabolism.

• Gender:
  Women may experience higher susceptibility to certain ADRs, e.g., longer QTc intervals leading to torsade de pointes, and psychiatric effects from anti-malarials like mefloquine.

• Co-morbidities & Concomitant Drugs:
  Conditions like hepatic or renal impairment and polypharmacy increase ADR risk due to altered pharmacokinetics and pharmacodynamics, and drug interactions.

• Ethnicity:
  Genetic traits influence drug metabolism, affecting ADR susceptibility. For example, increased angioedema risk with ACE inhibitors in Africans, or higher myopathy risk with rosuvastatin in Asians.

• Genetics:
  Variations such as slow or rapid acetylators, polymorphic enzymes, and hereditary conditions (e.g., malignant hyperthermia) significantly impact individual drug responses and ADR risk.

• Immunological Reactions:
  Allergic responses involve immune recognition of drugs as foreign, leading to reactions ranging from rashes to anaphylaxis. Prior exposure is typically required.

• Prevention & Monitoring:
  Strategies include reviewing patient history, rational prescribing, patient education, and regular monitoring of drug effects and organ functions to reduce preventable ADRs.

💡 Key Takeaway

Individual susceptibility to adverse drug reactions is influenced by genetic, physiological, and environmental factors; understanding these factors enables personalized approaches to minimize risks and improve patient safety.

📖 8. Genetics & Drug Response

🔑 Key Concepts & Definitions

• Pharmacogenetics: The study of how individual genetic variations influence drug treatment outcomes.
• Pharmacogenomics: The broader analysis of how the entire genome affects drug response, leading to personalized medicine.
• Genetic Polymorphism: Variations in DNA sequences among individuals that can alter drug metabolism or response.
• Atypical Plasma Cholinesterase: Genetic variation affecting the breakdown of certain drugs like succinylcholine, impacting their duration of action.
• Hereditary Warfarin Resistance: Genetic factors influencing warfarin sensitivity, affecting dosing and risk of bleeding.
• Immune-mediated Reactions: Allergic responses triggered by drugs, involving immune system recognition of drugs as foreign.

📝 Essential Points

• Genetic differences significantly impact drug metabolism, efficacy, and toxicity, contributing to variability in drug response.
• Variations in enzymes such as acetyltransferases and cytochrome P450 can classify individuals as slow, intermediate, or rapid metabolizers, affecting drug clearance.
• Pharmacogenetics enables identification of genetic markers to predict adverse reactions and optimize drug dosing.
• Inherited traits can cause resistance or hypersensitivity to certain drugs, such as warfarin or heparin.
• Immunological reactions are independent of pharmacological effects and require prior sensitization; they can range from mild rashes to severe anaphylaxis.
• Ethnic differences influence drug response and adverse event susceptibility, e.g., increased angioedema risk with ACE inhibitors in Africans.
• Monitoring genetic markers and drug levels can prevent adverse drug reactions, especially in vulnerable populations like children and the elderly.
• Causality assessment tools, such as the Naranjo algorithm, help determine the likelihood that a drug caused an adverse event.

💡 Key Takeaway

Genetic variability plays a crucial role in individual drug responses, and understanding pharmacogenetics is essential for personalized therapy to minimize adverse reactions and improve efficacy.

📖 9. Immunological & Allergic Reactions

🔑 Key Concepts & Definitions

• Allergic Reaction: An immune response to a drug that involves recognition of the drug as a foreign antigen, leading to immune-mediated tissue damage or symptoms.
• Type I Hypersensitivity: Immediate allergic reaction mediated by IgE antibodies, resulting in mast cell degranulation (e.g., anaphylaxis, urticaria).
• Type II Hypersensitivity: Cytotoxic reaction involving IgG or IgM antibodies directed against cell surface antigens, causing cell destruction (e.g., hemolytic anemia).
• Type III Hypersensitivity: Immune complex-mediated reactions where antigen-antibody complexes deposit in tissues, causing inflammation (e.g., serum sickness).
• Type IV Hypersensitivity: Delayed-type hypersensitivity mediated by T cells, leading to tissue damage (e.g., contact dermatitis).
• Sensitization: The process by which prior exposure to a drug primes the immune system for a hypersensitive response upon subsequent exposure.

📝 Essential Points

• Immunological reactions are independent of the drug's pharmacological action; prior exposure is typically required.
• Small molecules can bind to proteins, forming hapten-protein complexes that trigger immune responses.
• Patients with atopic or allergic histories are at higher risk of immunological reactions.
• Types of reactions include immediate (Type I), cytotoxic (Type II), immune complex (Type III), and delayed (Type IV).
• Severe reactions such as anaphylaxis and serum sickness can be life-threatening.
• Causality assessment tools like the Naranjo algorithm help determine the likelihood that a drug caused an immunological adverse event.
• Prevention involves identifying at-risk patients, avoiding known allergens, and monitoring for early signs of hypersensitivity.
• Management may include drug withdrawal, antihistamines, corticosteroids, or emergency interventions for anaphylaxis.

💡 Key Takeaway

Immunological and allergic reactions to drugs are immune-mediated responses that can range from mild to life-threatening; understanding their mechanisms, risk factors, and prevention strategies is essential for safe pharmacotherapy.

📖 10. Causality & Assessment Methods

🔑 Key Concepts & Definitions

• Adverse Drug Reaction (ADR): A noxious, unintended response to a drug occurring at normal doses used for treatment, diagnosis, or prophylaxis, without the need to prove a pharmacological mechanism.
• Adverse Drug Event (ADE): An adverse outcome after drug use, which may or may not be causally linked to the drug; all ADRs are ADEs, but not all ADEs are ADRs.
• Causality Assessment: The process of determining whether a drug is responsible for an adverse event, often using structured tools like the Naranjo algorithm.
• Naranjo Algorithm: A questionnaire-based method assigning scores to various factors (timing, dechallenge, rechallenge, alternative causes) to classify the likelihood of a causal relationship as highly probable, probable, possible, or doubtful.
• Serious Adverse Event: An adverse event resulting in death, life-threatening situation, hospitalization, disability, or congenital anomaly.
• Preventability of ADRs: Most ADRs are preventable through careful monitoring, thorough patient history, rational prescribing, and patient education.

📝 Essential Points

• Epidemiology: ADRs account for 2.6%-6.5% of hospital admissions, with 3.5%-14.7% of inpatients affected, and are a leading cause of death (4th-6th in the USA).
• Classification of ADRs (Rawlins-Thompson):
  • Type A: Predictable, dose-dependent, common, and preventable (e.g., bradycardia from β-blockers).
  • Type B: Unpredictable, immune-mediated or idiosyncratic, often serious (e.g., hepatotoxicity, allergic reactions).
  • Type C: Dose and time-related, related to cumulative dose (e.g., corticosteroid suppression).
  • Type D: Delayed effects, occurring after some time (e.g., carcinogenesis).
  • Type E: Occur after drug withdrawal (e.g., withdrawal syndrome).
  • Type F: Unexpected therapy failure, often due to drug interactions (e.g., contraceptive failure with enzyme inducers).
• Factors Influencing Susceptibility: Age (elderly and children), gender, co-morbidities, ethnicity, pharmacogenetics, and immunological factors.
• Pharmacogenetics & Pharmacogenomics: Variability in genes affecting drug metabolism and response, leading to personalized medicine approaches.
• Immunological Reactions: Allergic responses that are independent of pharmacological effects, requiring prior exposure, and classified into types I-IV.
• Assessment & Prevention: Use of causality algorithms like Naranjo, thorough patient history, monitoring, and clear communication to reduce preventable ADRs.

💡 Key Takeaway

Causality assessment methods, especially structured algorithms like Naranjo, are essential tools in determining the likelihood of a drug causing an adverse event, enabling targeted prevention, management, and informed patient care.

⚠️ Common Pitfalls & Confusions

1. Confusing Side Effects with ADRs—side effects are pharmacologically related, ADRs are noxious and unintended.
2. Assuming all ADEs are ADRs—some ADEs are unrelated or incidental.
3. Overlooking genetic factors influencing drug response and ADR risk.
4. Misclassifying Type B ADRs as predictable or preventable.
5. Ignoring the role of immune mechanisms in allergic reactions.
6. Failing to differentiate between ADRs and toxicity—toxicity often involves overdose.
7. Underestimating susceptibility factors like age, gender, and co-morbidities.
8. Relying solely on clinical presentation without causality assessment tools.
9. Neglecting delayed ADRs (Type D) that manifest long after drug exposure.
10. Overlooking drug interactions as F-type ADRs leading to therapy failure.

✅ Exam Checklist

• Define ADR, side effect, and ADE; distinguish their differences.
• List and describe the Rawlins-Thompson classification of ADRs.
• Explain the pharmacological mechanisms underlying ADRs.
• Identify factors influencing individual susceptibility to ADRs.
• Discuss the role of pharmacogenetics and pharmacogenomics in drug response.
• Describe immunological and allergic reactions related to ADRs.
• Outline methods for causality assessment, such as the Naranjo algorithm.
• Recognize common preventable ADRs and strategies for their mitigation.
• Differentiate between predictable (Type A) and unpredictable (Type B) ADRs.
• Understand the epidemiology and impact of ADRs on healthcare.
• Explain the significance of genetic variations in drug metabolism and ADR risk.
• Identify delayed (Type D) and withdrawal (Type E) ADRs.