Allergies to antibiotics are often confused with common side effects of the drugs. True allergies cause reactions that may worsen the next time a person takes the drug. Fewer than 25 percent of reported drug allergies are caused by allergy rather than side effects, J.M. Langley, M.D. reports in the May/June 2002, issue of "Canadian Journal of Infectious Disease." While 10 percent of people report an allergy to penicillin, the most common drug allergy, most can actually take the drug without a reaction, Roland Solensky, MD reports on UpToDate. Allergic symptoms can occur from any antibiotic.
Rash
While many people taking antibiotics develop a rash, it's difficult to determine whether the rash is an allergic reaction, a side effect of the illness being treated or a reaction between the drug and the illness. Up to 13 percent of children taking ampicillin or amoxicillin, both penicillin derivatives, develop a rash, Langley states, but most are not considered to be allergic to penicillin. This rash, called a toxic rash, looks like small pink spots that occur mostly on the stomach, back and chest, according to the Milton S. Hershey Medical Center College of Medicine. Rashes that occur with a true allergic reaction usually itch.
Hives
Hives, raised, red, itchy welts that appear and disappear over a period of several days, generally indicate a true allergic reaction to a drug. Hives on the face can cause swelling around the eyes, lips and tongue. While hives occur on the surface of the skin, a deeper reaction known as angioedema can cause more severe facial swelling. Taking antihistamines reduces the itching and swelling that accompanies hives; steroids may be prescribed in severe cases to reduce the immune response that allergies trigger.
Respiratory Symptoms
Because swelling often occurs in allergic reactions, wheezing or tightness in the chest can occur. Extreme shortness of breath and chest tightness indicates a more serious reaction called anaphylaxis that needs immediate medical treatment. Epinephrine, also called adrenaline, may be required in severe cases of respiratory symptoms.
Anaphylaxis
Anaphylaxis, a life-threatening symptom of drug allergy, occurs suddenly, usually within minutes of taking a drug, and requires immediate medical treatment. Symptoms of anaphylaxis include shortness of breath, weakness, dizziness, nausea, vomiting or diarrhea and a rapid heartbeat, MayoClinic.com states. Collapse, loss of consciousness and death can occur without rapid treatment with epinephrine, which stimulates the heart and relaxes the airways, decreasing the constriction so air can reach the lungs.
