Why pharmacovigilance matters: the burden of adverse drug reactions
Pharmacovigilance (literally a watch kept over medicines) is the identification, assessment and prevention of adverse drug reactions, meaning unwanted harmful effects of medicines, once a drug is in use.
Remember
Adverse drug reactions cause a substantial share of hospital admissions and can lengthen stays, and many are avoidable, so safety monitoring has to continue once a medicine is in use.
An adverse drug reaction (ADR) is a harmful and unintended effect of a medicine. Pharmacovigilance is the work of identifying, assessing and preventing these reactions once a medicine is in use. In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) runs the Yellow Card Scheme, which collects reports of suspected reactions.
It matters because of the size of the harm. A study published in 2004 looked at 18,820 patients admitted to two Merseyside hospitals. In 6.5% of admissions an adverse drug reaction was involved, and in 80% of those the reaction directly caused the admission. These admissions used about 4% of hospital bed capacity, and the projected cost to the NHS was 466 million pounds a year. Most of the reactions were judged definitely or possibly avoidable, so watching for them can prevent harm and not just record it. This is an illustration, not a current national figure: it is a historical two-hospital finding.
The second reason is that a licence is the start of safety evaluation, not the end. Trials before licensing (before a medicine reaches the market) are usually small, short and selective, meaning the patients are selected and may under-represent older people and those taking several medicines. A reaction affecting 1 in 10,000 people, or one that appears after years of use, can therefore be missed. Pooled reports across a whole population show patterns that no single doctor would see. One Yellow Card report is a signal for the MHRA to investigate, and not proof of cause.
Key facts
- Definition
- pharmacovigilance is the identification, assessment and prevention of adverse drug reactions once a medicine is in use.
- The burden
- a 2004 study of 18,820 admissions at two Merseyside hospitals linked an adverse drug reaction to 6.5% of them, and in 80% of that subset the reaction directly caused the admission.
- Caveat
- the 6.5% is a historical two-hospital finding, not a current estimate for all UK admissions.
- Avoidability
- most of the reactions were judged definitely or possibly avoidable, so active surveillance (systematically looking for reactions rather than waiting for them to be noticed) can prevent harm and not just record it.
- Limits of trials
- trials before licensing are usually small, short and selective, so rare or delayed reactions can be missed.
- UK system
- the MHRA runs the Yellow Card Scheme for reporting suspected adverse drug reactions.
- Single reports
- one Yellow Card report is a signal to investigate, not proof of cause.
Exam traps
- A Yellow Card report does not prove that a medicine caused a reaction, because it records a suspicion and works as a signal for the MHRA to investigate.
- Adverse drug reactions are not confined to newly licensed medicines, because the drugs most commonly implicated in the Merseyside admissions were long-established ones such as low-dose aspirin and diuretics.
- The 6.5% from Merseyside is not a current estimate for all UK admissions, because it came from a historical study of two hospitals and illustrates the burden.
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