Drug hypersensitivity, or an allergic reaction, occurs when either the drug or its metabolites triggers the immune system and is not predictable. Hypersensitivity is produced with repeated exposure to the same drug. Signs of a true allergy include skin rash, itching, hives, respiratory distress and rhinitis. Other hematologic signs of allergy include hemolytic anemia, agranulocytosis and thrombocytopenia.6 An individual may take a drug nine times, and have an allergic reaction the tenth time. Serious, life-threatening reactions are rare, and include anaphylaxis, hemolysis, and bone marrow suppression. 5,6The penicillins are the most common cause of drug-induced anaphylaxis, affecting one in every 50,000 individuals exposed.6
