Adverse Drug Reaction
An adverse drug reaction (ADR) is an unwanted or harmful reaction to a medication that occurs at doses normally used for the prevention, diagnosis, or treatment of disease.
Definition and Classification
ADRs can be classified into two main categories: type A and type B. Type A reactions are predictable, dose-dependent, and often related to the pharmacological effect of the drug. Type B reactions are unpredictable, not dose-dependent, and may be due to an allergic or idiosyncratic response.
Type A Reactions
Type A reactions are the most common type of ADR and account for approximately 80% of all ADRs. They are often related to the pharmacological effect of the drug and can be predicted based on the drug's mechanism of action. Examples of type A reactions include:
- Gastrointestinal upset caused by nonsteroidal anti-inflammatory drugs (NSAIDs)
- Respiratory depression caused by opioids
- Hypotension caused by antihypertensive medications
Type B Reactions
Type B reactions are less common than type A reactions and account for approximately 20% of all ADRs. They are often unpredictable and may be due to an allergic or idiosyncratic response. Examples of type B reactions include:
- Anaphylaxis caused by penicillin
- Stevens-Johnson syndrome caused by sulfonamides
- Toxic epidermal necrolysis caused by carbamazepine
Causes and Risk Factors
Several factors can increase the risk of an ADR, including:
- Age: elderly patients are more susceptible to ADRs due to decreased renal function, polypharmacy, and age-related changes in drug metabolism
- Polypharmacy: taking multiple medications increases the risk of ADRs due to potential drug interactions
- Genetic predisposition: some individuals may be more susceptible to ADRs due to genetic variations that affect drug metabolism
- Dose and duration of treatment: higher doses and longer durations of treatment increase the risk of ADRs
Symptoms and Diagnosis
The symptoms of an ADR can vary widely depending on the medication, dose, and individual response. Common symptoms include:
- Rash or skin lesions
- Gastrointestinal upset (nausea, vomiting, diarrhea)
- Headache or dizziness
- Fatigue or weakness
Diagnosis of an ADR is often based on a combination of clinical presentation, medical history, and laboratory tests. The Naranjo algorithm is a widely used tool for assessing the likelihood of an ADR.
Treatment and Prevention
Treatment of an ADR typically involves discontinuing the offending medication and providing supportive care. In some cases, treatment may involve administering antidotes or using medications to counteract the effects of the ADR.
Prevention of ADRs is critical and can be achieved through:
- Close monitoring of patients for signs and symptoms of ADRs
- Use of medication reconciliation to minimize polypharmacy
- Education of patients and healthcare providers about potential ADRs
- Use of electronic health records to track medication use and potential interactions
Conclusion
Adverse drug reactions are a significant concern in healthcare, with potentially serious consequences for patients. Understanding the definition, classification, causes, risk factors, symptoms, diagnosis, treatment, and prevention of ADRs is essential for providing high-quality patient care.
Article last updated on: 15th June 2025.
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