The World Health Organization (WHO) defines adverse drug reactions (ADR) as “any response to a drug which is noxious and unintended, and which occurs at doses normally used in man”. Importantly, these refer to situations when the drug is used normally and at the recommended dosages. ADRs may be classified into six categories, based on the underlying causes and characteristic features, as outlined in Table 1 below:
|Reaction Type||Alternative Names||Features||Examples|
|Type A||Dose-related reactions|
|The exaggerated but normal pharmacological response to a specific drug|
Type A reactions vary with the dose and can be predicted
Management includes reducing the dosage or usage of an alternative agent
|Xerostomia with tricyclic antidepressants|
Sensorineural hearing loss from aminoglycoside overdose
Respiratory depression with opioids
|Type B||Non-dose-related reactions|
|A response that is not expected based on the pharmacological action of the drug|
Unpredictable, with no relation to dose (i.e., idiosyncratic)
Any dose may be sufficient to trigger such reactions
Allergies and anaphylaxis are classified as type B reactions
Uncommon and frequently severe
Aplastic anaemia by chloramphenicol
|Type C||Dose and time-related reactions|
|Chronic reactions which persist for longer periods|
The drug must be withheld for a long time for resolution
Related to the dose accumulation or prolonged use of a drug
Osteonecrosis of the jaw by bisphosphonates
Adrenal suppression with corticosteroids
|Type D||Time-related reactions|
|Type D reactions will occur a significant period after the drug is used|
Linking the drug and ADR is, therefore, more challenging
|Thrombocytopenia and leukopenia with lomustineTeratogenesis|
Tardive dyskinesia with antipsychotics
|Type E||Withdrawal reactions|
|Occurs after cessation of use|
Restarting the drug will lessen the reaction
|Withdrawal from opiates or benzodiazepines|
Myocardial infarction after beta-adrenergic antagonist cessation (i.e., beta-blockers)
|Type F||Failure of therapeutic efficacy||The drug undesirably decreases or increases its efficacy|
Dose-related and is linked to drug-drug interactions
May be mitigated by increasing the dose or removing any concurrent drugs which may be interfering
|Reduced drug clearance due to renal failure|
ADRs result in significant morbidity, with 1 in 16 patients being hospitalised for a serious reaction, and 2% of admitted patients dying due to the ADR. Moreover, studies have reported that ADRs occur in 10 to 20% of patients who are hospitalised for other reasons. As such, the detection and reporting of ADRs is a critical responsibility of healthcare professionals involved, to maintain patient safety. This is the concept of pharmacovigilance.
Reporting ADRs is most often carried out by healthcare professionals; however, patients may also report reactions to the relevant authorities. However, it is recommended that patients first speak to their physician before such reporting to avoid any erroneous reporting.
While such ADR reporting has been carried out for decades by various regulatory authorities worldwide using varying modalities, in recent years it has become more streamlined, with similar data being collected in different countries to allow data to be compared. Reporting is now often carried out via online reporting forms (rather than paper forms), which vary depending on the country. A list of national medicine regulatory authorities within the European Union can be found here, and the individual national websites all include the relevant ADR reporting forms to be filled out. In the United States, the FDA similarly uses the “MedWatch online voluntary reporting form”. In the United Kingdom, the so-called Yellow Card reporting system has been updated. The system ensures that all patient data inputted remains confidential, and while some reporter data is collected, this is destroyed after the report is inserted into the database.
Typically, the following data is collected by all medical authorities, with the aim of understanding what occurred and establishing whether there exists a link between the unwanted effect experienced and a specific drug:
Once the form is filled, it is submitted to the respective medicines authority, which will then transmit the report to the EU central side effect database “Eudravigilance” in the case of European countries; the FDA in the United States; or the Medicines & Healthcare Products Regulatory Agency in the United Kingdom. The report will then be analysed and assessed on whether it was a true ADR. Regulatory actions may then be taken as needed, to safeguard patients’ wellbeing.
The contribution of all healthcare professionals to ADR reporting is key in the ongoing search and development of safer drugs for all.
- List of National Regulatory Authorities
- MedWatch online voluntary Reporting Form
- Yellow Card Reporting System
Written by Robert Pisani (Medical Student)
Reviewed by Professor Janet Mifsud
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