Reporting Adverse Drug Reactions

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 TypeAlternative NamesFeaturesExamples
Type ADose-related reactions

Augmented reactions
The exaggerated but normal pharmacological response to a specific drug
Type A reactions vary with the dose and can be predicted
Rarely severe
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 BNon-dose-related reactions

Bizarre 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
Drug-induced anaphylaxis
Antibiotic-associated colitis
Aplastic anaemia by chloramphenicol
Type CDose and time-related reactions

Chronic 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
Steroid-induced osteoporosis
Osteonecrosis of the jaw by bisphosphonates
Adrenal suppression with corticosteroids
Type DTime-related reactions

Delayed 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 EWithdrawal reactions

End-of-use 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 FFailure of therapeutic efficacyThe drug undesirably decreases or increases its efficacy
Dose-related and is linked to drug-drug interactions
Relatively common
May be mitigated by increasing the dose or removing any concurrent drugs which may be interfering
Reduced drug clearance due to renal failure
Antibiotic resistance
Table 1: Overview of ADR types, including their alternative names, features and named drug examples.

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:

  • The affected patient’s demographics (e.g., age, gender, weight, ethnicity)
  • The reason for the report:
    • A reaction to a specific drug
    • An ADR is due to an error in medication use, such as occupational exposure or abuse
    • A problem with the product, such as defects
    • Issues with different manufacturers of the same drug
  • The severity and outcome of the ADR (e.g., fatal, life-threatening, caused hospitalisation)
  • Date of event
  • A description of the event:
    • The suspected drug which caused the ADR
    • The reaction itself
    • Information on any concomitant drugs being used at the time
    • Relevant laboratory data if applicable
  • Management of ADR (e.g., the medication stopped or medicine was restarted)
  • Whether the drug in question is still available
  • Information about the product itself (e.g., name, batch number, manufacturer)
  • Patient co-morbidities (e.g., allergies, liver disease, pregnancy)
  • Reporter details

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.

Useful Links

Written by Robert Pisani (Medical Student)
Reviewed by Professor Janet Mifsud

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