Question: What exactly does it mean to be allergic to certain medications?
Answer: Drug allergy is a form of adverse drug reaction. It's important to realize that not all reactions to drugs are allergic reactions, only some of them, in fact a minority of reactions to drugs are allergic.
What that means is, is that they are immunologically mediated -- meaning that the immune system is causing the drug reaction.
So there are various types of allergic drug reactions.
The one we think of most often is the type mediated by allergy antibodies -- or IGE antibodies. And the types of reactions in this category include hives, swelling of the lips and the tongue, swelling of the larynx, as well as a very severe form of this type of reaction which is anaphylaxis -- which is a severe allergic reaction to a drug where your blood pressure may fall and you will also have hives as well as shortness of breath.
Now, there are other types of allergic drug reactions that are caused by the immune system as well. And these are mediated by different types of antibodies -- not allergy antibodies -- but other antibodies that actually respond to the drug, leading to such things such as hemolysis, which is breakdown of the red blood cells, or serum sickness reactions, where you get fever and chills, or other types of reactions that may involve the skin.
So, immune-mediated drug reactions are a type of adverse reaction, and we call these allergic drug reactions and there may be several types.