Recognizing, Reporting, and Reducing Adverse Drug Reactions

South Med J. 2001;94(4) 

In This Article


An ADR is defined as any undesirable or unexpected event that requires some change in the clinician's care of the patient, including discontinuing the medication, modifying the dose, prolonging hospitalization, or initiating supportive care. This does not encompass drug withdrawal, abuse, overdose, or error in administration.[1] Although ADRs have several classifications, most generally include two basic types: predictable and unpredictable. Predictable, or type A, reactions occur when the normal effects of drugs are exaggerated to the point of being undesirable. They are dose-dependent and related to the expected pharmacologic action of the drugs. These are the most common types of reactions.

Unpredictable, or type B, reactions occur when there is an effect from medication use that is unrelated to the drug's known pharmacologic action. These include idiosyncratic, immunologic, allergic, carcinogenic, and teratogenic reactions. Again, this classification system makes a distinction between ADR and error in administration.


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