Overview
Penicillin allergy is a reaction of the immune system to the antibiotic medicine penicillin. Penicillin is used to treat bacterial infections.
Penicillin allergy may cause hives, rash and itching. A serious reaction can include anaphylaxis. Anaphylaxis is a life-threatening condition that can cause throat swelling and trouble breathing.
Research has shown that penicillin allergies may be over-reported. When allergies are over-reported, it can result in the use of improper and more-expensive antibiotic treatments. Therefore, to ensure the best treatment options in the future, an accurate diagnosis is needed when penicillin allergy is suspected.
Other antibiotics, such as those similar to penicillin, also can result in allergic reactions.
Symptoms
Symptoms of penicillin allergy often happen within an hour after taking the antibiotic. Less commonly, reactions can happen hours, days or weeks later.
Penicillin allergy symptoms may include:
- Skin rash.
- Hives.
- Itching.
- Fever.
- Swelling.
- Shortness of breath.
- Wheezing.
- Runny nose.
- Itchy, watery eyes.
- Anaphylaxis.
Anaphylaxis
Anaphylaxis is a rare, life-threatening allergic reaction that causes problems in multiple parts of the body. Symptoms of anaphylaxis include:
- Tightening of the airways and throat, causing breathing problems.
- Nausea or stomach cramps.
- Vomiting or diarrhea.
- Dizziness or lightheadedness.
- Weak, rapid pulse.
- Drop in blood pressure.
- Seizures.
- Loss of consciousness.
Delayed reactions resulting from penicillin allergy
Less common penicillin allergy reactions happen days or weeks after exposure. Reactions may continue for some time after you stop taking the antibiotic. These conditions include:
- Serum sickness, which may cause fever, joint pain, rash, swelling and nausea.
- Anemia. Anemia is a reduction in red blood cells caused by the medicine. It can cause fatigue, irregular heartbeats, shortness of breath and other symptoms.
- Drug reaction with eosinophilia and systemic symptoms, also called DRESS. DRESS causes rash, high white blood cell counts, general swelling and swollen lymph nodes. DRESS also can cause hepatitis infections to come back.
- Stevens-Johnson syndrome or toxic epidermal necrolysis, which involves serious blistering and peeling of the skin.
- Inflammation in the kidneys, called nephritis. Nephritis can cause fever, blood in the urine, general swelling, confusion and other symptoms.
Adverse events that are not allergic reactions
You may experience side effects of penicillin that are not an allergic reaction to the antibiotic. This also can happen with other medicines. Depending on the type of penicillin, common side effects may include mild nausea or diarrhea, headache, or vaginal itching. Unrelated symptoms or symptoms of an infection for which you are being treated also may be mistaken as an allergic reaction to medicine.
When to see a doctor
Make an appointment with your doctor or other healthcare professional if you have any lasting symptoms that worry you. It's important to understand and discuss what is an allergic reaction, what is a typical side effect and what you can tolerate in taking a medicine.
Call 911 or emergency medical help if you experience symptoms of a serious reaction or possible anaphylaxis after taking penicillin.
Drug rash
A medicine rash usually starts within two weeks of taking a new medicine. The rash begins as small spots that spread. It can cover large areas of the body.
Causes
Penicillin allergy happens when the immune system becomes overly sensitive to the antibiotic. The immune system reacts to the medicine as if it were a harmful substance, such as a viral or bacterial infection.
Before the immune system can become sensitive to penicillin, you have to be exposed to the medicine at least once. If and when your immune system thinks penicillin is a harmful substance, it develops an antibody to the medicine.
The next time you take the medicine, these specific antibodies flag it and attack the substance. Chemicals released by this activity cause the symptoms related to an allergic reaction.
Being exposed to penicillin in the past may not have been something you noticed. Some evidence suggests that very small amounts of penicillin in the food supply may be enough for the immune system to create an antibody to it.
Penicillins and related medicines
Penicillins belong to a class of antibacterial medicines called beta-lactam antibiotics. Although these medicines are slightly different from one another, they generally fight infections by attacking the walls of bacterial cells. In addition to penicillins, other beta-lactams more commonly related to allergic reactions are a group called cephalosporins.
If you've had an allergic reaction to one type of penicillin, you could be allergic to other types of penicillin or to some cephalosporins.
Penicillins include:
- Amoxicillin.
- Ampicillin.
- Dicloxacillin.
- Nafcillin.
- Oxacillin.
- Penicillin G.
- Penicillin V.
- Piperacillin.
- Ticarcillin.
Cephalosporins include:
- Cefaclor.
- Cefadroxil.
- Cefazolin.
- Cefdinir.
- Cefepime.
- Cefotetan.
- Cefprozil.
- Cefuroxime.
- Cephalexin.
Risk factors
While anyone can have an allergic reaction to penicillin, a few factors can increase the risk. These include:
- A history of other allergies, such as food allergy or hay fever.
- An allergic reaction to another medicine.
- A family history of medicine allergy.
- Increased exposure to penicillin because of using high doses or using the medicine often or over long periods of time.
- Certain illnesses commonly related to allergic medicine reactions, such as infection with HIV or the Epstein-Barr virus.
Prevention
If you have a penicillin allergy, the simplest prevention is to avoid the medicine. Steps you can take to protect yourself include the following:
- Inform healthcare workers. Be sure that your penicillin allergy or other antibiotic allergy is clearly identified in your medical records. Inform other healthcare professionals, such as your dentist.
- Wear a bracelet. Wear a medical alert bracelet that identifies your allergy. This information can ensure proper treatment in an emergency.