Drug Allergy:
An abnormal mechanism of drug response that occurs in individuals who produce injurious antibodies that react with foreign substances-- in this instance, a drug. The person who is allergic by nature and has a history of hay fever, asthma, hives, or eczema is more likely to develop drug allergies. Allergic reactions to drugs take many forms: skin eruptions of various kinds, fever, swollen glands, painful joints, jaundice, interference with breathing, acute collapse of circulation, etc. Drug allergies can develop gradually over a long period of time, or they can appear with dramatic suddenness and require life-saving intervention.
--From The Essential Guide to Prescription Drugs | 
