A drug allergy is an immunologic reaction to a medication and should be distinguished from a non-immunologic adverse drug reaction. All medications potentially have side effects, which may or may not be related to the drug’s mechanism of action. Side effects may include nausea, vomiting, diarrhea, muscle aches, headache, fatigue, drowsiness, or insomnia. Examples of non immunologic, non-allergic reactions to drugs are: Muscle cramping after taking Lipitor and other statins, stomach upset or intestinal bleeding from aspirin and NSAIDs (non=steroidal anti-inflammatory drugs such as Motrin or Naprosyn), drowsiness from antihistamines or tranquilizers, and worsening of asthma from Beta-blockers (Atenolol, metoprolol, propranolol, Corgard®, Coreg® and others)
A drug allergy is not a side effect and may result in itching, rash, hives, facial swelling, difficulty breathing, and a drop in blood pressure. Typically, an allergic reaction to a drug will not occur the first time the medication is taken. The immune system needs to be exposed (or sensitized) to the drug before a reaction can develop.
Sensitization to one drug may lead to an allergic reaction to another drug in the same class, such as for penicillin-derived antibiotics or non-steroidal anti-inflammatory drugs (NSAIDs). Common allergic drug reactions are skin rashes itching and hives to penicillin, asthma exacerbation from ASA and NSAIDs.
A severe allergic reaction to a drug may lead to anaphylaxis, which is an acute and sometimes catastrophic reaction with symptoms of warm skin, flushing, hives, swelling (angioedema) of the body, particularly of the throat, wheezing, nausea, vomiting, abdominal cramping, diarrhea, and low blood pressure, including shock, and in severe cases, loss of consciousness and even death. Anaphylaxis is an emergency that requires immediate medical attention by a physician, and treatment particularly with injection intra-muscularly with epinephrine (adrenalin).
If you are concerned that you have a drug allergy, please consult with your primary care physician, who may decide that you may need evaluation by an allergist, including skin testing, which is available only for a few drugs such as penicillin. Very important in my opinion is for the allergist to take a careful history do a careful physical exam. Documentation of the name of the drug, route of administration, date of dosing, and reaction is very important. The allergist will conclude at the end of the visit or visits whether he/she thinks this was a drug allergy or drug non-allergic reaction.