ALLERGIC DRUG-REACTIONS - INCIDENCE AND AVOIDANCE

Allergic drug reactions may be responsible for about 10% of all advers e drug reactions. However, in studies of hospital admissions, which in evitably consider the more severe cases, up to 20% of admissions for a dverse drug reactions may be due to immunological mechanisms. There ar e few community-based studies. In a study of unselected normal individ uals, about 14.7% gave a history of allergic-type reactions to 1 or mo re drugs. Such reactions are more common in atopic patients. The incid ence of allergic reactions to particular drugs should also be consider ed. The penicillins are probably the best studied drugs in this respec t. They cause serious allergic reactions in 1 in 5000 to 10 000 exposu res. The avoidance of allergic drug reactions requires the identificat ion of patients at risk. This may be done by taking a general medical history (for instance, a history of atopy) and/or specific drug histor y (previous drug-related adverse events, and the nature of the event), diagnostic testing (available for only a few drugs), and ultimately r echallenge, with its attendant dangers. Allergy to penicillins can be detected by skin testing in 80% of patients. Radioallergosorbent tests (RAST) are slightly less sensitive. Patients in whom the allergy is p resumably to the sidearm of a semisynthetic penicillin have been descr ibed. These patients may not be allergic to benzylpenicillin and their allergy is not detectable by standard skin testing. In the rare circu mstance where patients must be treated with a drug to which they are a llergic, desensitisation is sometimes possible but may be hazardous. M ost physicians do not perform further investigation of patients suspec ted of an allergy, but rather advise them to avoid future exposure to the suspected allergen.