Understanding drug allergies.

At this time, the incidence of adverse drug reactions can only be estimated because the intensive monitoring and documenting that is required to make this determination does not exist at most hospitals and clinics. Despite these limitations, a meta-analysis of prospective studies has estimated the incidence of serious adverse drug reactions in hospitalized patients to be 6.7% and the incidence of fatal adverse drug reactions to be 0.32%. When evaluating and managing the condition of a patient who has experienced an adverse drug reaction, the physician first obtains an accurate history and performs a careful physical examination to determine whether the reaction was immunologic in nature. Drug reactions that are immunologically mediated (1) require a period of sensitization, (2) occur in a small proportion of the population, (3) are elicited at drug doses far below the therapeutic range, and (4) subside after drug discontinuation in most instances. All possible culprit drugs should be identified, with dosages and dates of administration and discontinuation, and the patient should be asked about any previous drug exposure history. Although immunodiagnostic tests for allergic drug reactions are limited, several tests do exist and may be useful in the identification of drug-specific antibodies, drug-specific T lymphocytes, or mediators from activated cells. If the reaction was not consistent with an IgE-mediated event and if it did not involve serious organ damage, cautious rechallenge may be considered. For those reactions that appear to be IgE-mediated and for which there is no reliable skin test reagent, drug desensitization may be performed by allergists who are trained in this procedure.