Adverse Drug Event (ADE)

The specific pharmacologic substance initiating the event. This includes prescription medications, over-the-counter drugs, biologics, and contrast media. Identification requires mapping brand names and generics to a common identifier like RxNorm to ensure the system recognizes the agent regardless of nomenclature. The trigger is the root node in the causal chain of the event.

A noxious and unintended response occurring at standard therapeutic doses. ADRs are a subset of ADEs characterized by a pharmacologic mechanism.

• Type A (Augmented): Dose-dependent and predictable (e.g., bradycardia from beta-blockers).
• Type B (Bizarre): Idiosyncratic and unpredictable (e.g., anaphylaxis). Distinguishing the mechanism is critical for determining preventability.

A preventable event occurring at any stage of the medication-use process—prescribing, transcribing, dispensing, administering, or monitoring.

• Omission Error: Failure to administer an ordered dose.
• Wrong Dose Error: A deviation from the prescribed amount. Medication errors may or may not cause harm, but when they do, they are classified as preventable ADEs.

The measurable injury resulting from the drug exposure. This is the defining characteristic that elevates a medication error or ADR to an ADE. Harm is graded by severity:

• Mild: Transient symptoms requiring no intervention.
• Moderate: Requires a change in therapy or prolonged hospitalization.
• Severe: Life-threatening or resulting in permanent disability.
• Fatal: Directly contributing to death.

The chronological link between drug administration and the onset of harm. Temporal reasoning algorithms analyze the sequence of events to establish causality.

• Dechallenge: Does the event resolve when the drug is stopped?
• Rechallenge: Does the event reappear if the drug is restarted? A plausible timeline is a primary criterion in causality assessment scales like the Naranjo Algorithm.

Intrinsic characteristics that alter the risk profile for an ADE. These are critical inputs for predictive models.

• Age: Neonates and geriatric patients have altered pharmacokinetics.
• Renal Function: Impaired clearance leads to drug accumulation (see Renal Dose Adjustment).
• Genomics: Variations in CYP450 enzymes cause aberrant metabolism.
• Polypharmacy: The Polypharmacy Risk Score quantifies cumulative risk from multiple agents.

A noxious and unintended response to a drug occurring at doses normally used for prophylaxis, diagnosis, or therapy. Unlike broader ADEs, ADRs are characterized by a causal relationship between the drug's pharmacological properties and the harmful outcome.

• Type A (Augmented): Dose-dependent and predictable, such as bleeding from anticoagulants
• Type B (Bizarre): Idiosyncratic and unpredictable, such as anaphylaxis from penicillin
• Type C (Chronic): Associated with long-term use, such as corticosteroid-induced osteoporosis
• Type D (Delayed): Carcinogenic or teratogenic effects appearing years later

A preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the healthcare professional, patient, or consumer. Medication errors can occur at any stage of the medication use process.

• Prescribing errors: Wrong drug, dose, route, or frequency
• Transcribing errors: Misinterpretation of orders during data entry
• Dispensing errors: Wrong medication or strength provided by pharmacy
• Administration errors: Wrong patient, time, or infusion rate
• Monitoring errors: Failure to review therapy for efficacy or toxicity

A retrospective chart review technique developed by the Institute for Healthcare Improvement that uses a defined list of clues, or triggers, to identify possible ADEs more efficiently than voluntary reporting alone.

• Medication triggers: Use of naloxone, vitamin K, or diphenhydramine as antidotes
• Laboratory triggers: Abrupt rise in serum creatinine or INR above therapeutic range
• Clinical triggers: Abrupt medication stop orders or transfer to higher level of care
• Yield: Detects 10-50x more ADEs than voluntary incident reporting systems

A standardized causality assessment tool consisting of 10 weighted questions that systematically evaluate the probability that a reported adverse event was actually caused by a specific drug rather than other factors.

• Scoring categories: Definite (≥9), Probable (5-8), Possible (1-4), Doubtful (≤0)
• Questions assess: Temporal relationship, dechallenge/rechallenge, alternative causes, objective evidence
• Limitations: Poor inter-rater reliability for certain reaction types; does not account for drug interactions
• Alternative tools: WHO-UMC causality categories and Liverpool ADR causality assessment tool

A structured evaluation framework distinguishing preventable ADEs from non-preventable ADRs, using explicit criteria to identify failures in the medication use system. This classification is critical for quality improvement and legal liability determination.

• Schumock-Thornton criteria: Evaluates if the drug was appropriate for the clinical condition, if dose/route/frequency were correct, and if therapeutic drug monitoring was performed
• Preventable ADEs result from medication errors that reach the patient
• Non-preventable ADRs occur despite appropriate prescribing and monitoring
• Ameliorable ADEs: Events whose severity could have been reduced with different management