Nonimmunologic adverse drug reactions. How to recognize and categorize some common reactions.

When a patient experiences an adverse drug reaction, the history is in most instances the only clinical tool available for establishing a diagnosis. Thus, when taking a history, physicians should always inquire about drugs the patient has been taking and prior reactions to drugs. Clinicians should characterize every adverse drug reaction according to an accepted classification system. Familiarity with the types of reactions discussed here is therefore essential. The majority of adverse drug reactions are nonimmunologic in origin, and the most common reactions occur in response to relatively few classes of drugs. It is important not to incorrectly label a reaction as allergic, since this implies an immune-mediated response, which often precludes future use of the drug. On the other hand, if there is any concern that a reaction may be allergic, it is best to err on the side of caution by using an alternative, non-cross-reacting drug for treatment.