17. Adverse Drug Reactions - Definition. Methods for detection. Pharmacoepidemiology.
Covers how new adverse drug reactions are detected, starting with a comparison table of methods such as clinical trials, spontaneous reporting, cohort studies, case-control studies and databases, with their strengths and weaknesses. It then explains cohort and case-control designs, a table of risk measures (absolute and relative risk, NNT, NNH) with a worked example, and the WHO-UMC causality categories with typical timing of different reactions.
Topic 17 of 30 in the MU Sofia syllabus for Clinical Pharmacology (Medicine, Year 5). The free AceMed note covers it in 6 sections, about 232 words (3 min of reading), with 16 flashcards.
In this note
Introduction
Methods of detection
Cohort study
Case–control study
Measures of risk
Assessing causality (WHO–UMC)
Introduction
New ADRs are found by several complementary methods. Pharmacoepidemiology applies epidemiological methods to the use and effects of drugs in large populations; it measures how often reactions occur and whether a drug really causes them.
Cohort study
Starts from exposure: follows a group taking the drug and a comparison group forward in time and compares how often the outcome occurs (e.g. venous thromboembolism with different contraceptives).
Advantages: prospective, less biased, measures incidence, good for common ADRs and new drugs.
Disadvantages: needs large numbers and years of follow-up; expensive.
Case–control study
Starts from the outcome: compares past drug exposure in people with the disease (cases) and matched people without it (controls). It showed, for example, the link between NSAIDs and GI bleeding, and between aspirin and Reye syndrome.
Advantages: quick, cheap, small samples, best for rare ADRs, several exposures studied at once.
Disadvantages: retrospective exposure data (recall bias), difficult choice of controls; gives the odds ratio, not incidence.
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