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Glossary of Pharmacology 

Adverse drug event


An Adverse Drug Event (ADE) is defined as “an injury resulting from medical intervention related to a drug, which includes errors in administration (Bates et. al. (1995) JAMA 274; 29-34).  Thus ADEs are a broad range of harms which include Adverse Drug Reactions (which are harms that occur when the correct drug is used in the correct dose and given via the correct route) but also drug errors in which an incorrect drug is given, a drug is given in overdose or a drug is given via the wrong route.


ADEs are unfortunately extremely common and as with Adverse Drug Reactions are a major problem for patients, families, health care providers, health care systems, government and industry.  Adverse Drug Events and medical errors are believed to be the third commonest cause of death in the United States with 100,000 Americans a year dying as a consequence of an ADE/medical error.   Adverse Drug Events appear to be more common among certain vulnerable populations such as very young children and older adults on multiple medications and special care must be taken when prescribing to these populations. Thus an understanding of the mechanism and importance of Adverse Drug Events is important for all health care providers. 

There are a number of potential approaches to reduce the risk of ADEs including the systems based approaches such as electronic prescribing systems.  While these approaches can reduce certain types of ADE they may also be associated with a risk for other types of ADEs. 

Examples of Adverse Drug Reactions: 


Adverse Drug Event 



10 fold error 

Error in calculating drug dose with the patient receiving 10 times the correct dose of intravenous morphine causing decreased level of consciousness and respiratory depression 

  • Pediatr 2012 May;129(5):916-24 

Glyburide and Glipizide 

Inadvertent substitution of one drug for another  

Both drugs are sulfonylureas used to treat diabetes with similar names; however they have different doses and dosing schedules and using one drug in the wrong dose can produce adverse effects such as hypoglycaemia 

  • Mayo Clin Proc 2014;89:1116-1125 


Mistaken administration of an oral formulation by the intravenous route, i.e. injection into the blood of a formulation intended to be taken by mouth 

Increased sedative effect and reduced level of consciousness as midazolam has 50% bioavailability; also potential for infection and to effects of injected excipients 

Teaching tips:  

Considerations around using Adverse Drug Events to inform teaching include: 

  • Understanding how Adverse Drug Events occur in the context of usual prescribing practices 

  • Appreciating the mechanism by which Adverse Drug Events produce harm, including the consequences of overdoses 

  • Communicating clearly with patients and families as when an Adverse Drug Event has occurred and how it was addressed 

  • Considering systems-based approaches to reducing the risk of preventable Adverse Drug Events 

    Suggested articles on this topic:

    • Wittich CM, Burkle CM, Lanier WL  Medication Errors:  An overview for clinicians Mayo Clin Proc 2014;89:1116-1125 
      - This manuscript reviews common issues leading to medication errors 
    • Makary M, Daniel M.  Medical error – the third leading cause of death in the US.  BMJ 2016; 353: 2139. 
      - This manuscript identifies medical errors as a major cause of death in the US and by extension other countries
    • Tariq RA, Vashisht R, Sinha A et al. Medication dispensing errors and prevention.!po=2.17391.
      - This is a review of medication errors including consideration on how they occur and how to prevent them 

    Linked terms: Adverse Drug Reactions, Drug Safety, Pharmacovigilance, Drug Allergy, Side Effects 

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