Virtually any medication has the potential to cause an allergic reaction in a susceptible individual. There is almost no way to predict whether you will develop an allergic reaction to a medication. In general, however, people who are allergy-prone are more likely to develop medication allergies. Be sure to tell your doctor about allergies you have as well as any unusual reactions you develop with a medication.
An allergic reaction can occur regardless of how much medication is taken or what the medication is designed to treat. The reaction may include an unexpected rash -- mild redness and itching ranks as the most common type of reaction -- or it may include swelling, hives, fever, blood changes such as anemia, or a host of other symptoms and signs. These reactions may appear suddenly or become apparent gradually, over time. Your doctor can help you determine whether your side effect is, in fact, an allergic reaction.
Anaphylaxis is the most severe and dangerous type of allergic reaction, and penicillin is the drug most often implicated in anaphylaxis. Anaphylaxis can be fatal in some cases if not treated promptly and properly. An anaphylactic reaction causes the victim's breathing passages to rapidly swell and spasm, which can make it difficult or even impossible to breathe. Life-threatening shock can also develop, with a precipitous drop in blood pressure and associated pallor, fast pulse, confusion, and nausea, with a potential loss of consciousness and cardiovascular collapse. People who know they are at risk for this type of severe allergic reaction should wear a bracelet (or necklace or card) that indicates that they have this allergy and they should also carry a solution of epinephrine (adrenaline) to inject immediately should they be exposed to the offending substance, known as the allergen. Epinephrine opens tightened airways, making it easier for the person to breathe, and constricts blood vessels to normalize blood pressure. Emergency medical help should be sought immediately.
Most allergic reactions to medication, however, are not life threatening. Consult your doctor regarding whether you should stop taking the medication. Antihistamines or steroids may be recommended. The most effective way to manage a medication allergy is to prevent yourself from becoming exposed to the allergen. Familiarize yourself with the genetic and brand names of the medications. Always examine over-the-counter medication labels to see if the allergen is among the ingredients.
Medications that bear a chemical relation to the one you are allergic to may
cause problems as well. If you are allergic to a cephalosporin antibiotic such
as cephalexin, for example, you may well react to another drug in the same
chemical class. Unfortunately, people are seldom aware of chemical relations
between drugs. Furthermore, the chemical similarity between drugs does not
necessarily mean that there will be cross-reactivity. Before receiving
medication remind your doctors, from your primary care doctor to your dentist,
of any history of allergies or allergic reactions.