Penicillins and cephalosporins are also the most common causes of drug allergy. About 10% of Americans report having an allergy to penicillin or a related antibiotic. In fact, though, the number of people who have a true penicillin allergy is much lower.
While penicillin allergy most frequently occurs in young adults, reactions can occur at any age. Women appear to be at higher risk than men. Reactions to penicillin may include hives, below-the-skin swelling, and asthma symptoms, as well as non-allergic symptoms such as serum sickness, certain forms of anemia, and rashes. In some cases a life-threatening reaction called anaphylaxis can occur.
This article will discuss how a true penicillin allergy is diagnosed, possible reactions, and what to do if you are allergic to penicillin but still need antibiotic treatment.
Family of Penicillin Antibiotics
The family of penicillin antibiotics includes:
Penicillin VK Penicillin G Dicloxacillin Oxacillin Nafcillin Amoxicillin Ampicillin Augmentin (amoxicillin/clavulanate) Unasyn (ampicillin/sulbactam) Zosyn (pipercillin/tazobactam)
The family of cephalosporins includes:
Keflex (cephalexin) Ancef (cefazolin) Ceftin (cefuroxime) Cefzil (cefprozil) Omnicef (cefdinir) Vantin (cefpodoxime) Many other antibiotics beginning with “cef-“ or “ceph-“
How Is a Penicillin Allergy Diagnosed?
While many people report having an allergy to penicillin, less than 5% of the population actually has a true allergy to the drug. Some patients who have been labeled as “penicillin allergic” may in fact have experienced non-allergic reactions or side effects to the drug, such as gastrointestinal upset, headache, or nausea, and mistaken it for a true allergy. Furthermore, most people lose their penicillin allergy over time—even patients with a history of severe reactions, such as anaphylaxis.
An oral challenge, which involves administering small doses of the drug under medical supervision, is the best, most effective method for diagnosing a penicillin allergy. However, healthcare providers often perform skin testing first to avoid the risk of allergic reaction, particularly among those with a medical history of penicillin sensitivity.
An extract called Pre-Pen (benzylpenicilloyl polylysine injection) is the only FDA-approved skin test for the diagnosis of penicillin allergy. Penicillin skin testing identifies the presence or absence of IgE antibodies to this injection and identifies the majority of cases of true clinical penicillin allergy. This information will allow a healthcare provider to decide if penicillin or an alternative antibiotic should be given.
Testing usually takes about an hour to complete. The skin is injected with weak solutions of various preparations of penicillin and observed for a reaction. This may cause itching, although it is not painful.
A positive skin reaction is indicated by an itchy, red bump that forms within about 30 minutes. People with a positive test are usually advised to continue avoiding penicillins. Not every test that is positive represents a true penicillin allergy, however; there are false positives in penicillin skin testing.
How Is a Penicillin Allergy Treated?
Other than treating drug allergy symptoms, the main treatment for penicillin allergy is avoidance of future use of penicillin and related antibiotics. However, if penicillin is required, people with penicillin allergy can also be admitted to a hospital for a desensitization procedure.
Complications
Most patients with true penicillin allergy can tolerate cephalosporins, but there are some cases where both penicillin antibiotics and cephalosporins need to be avoided. Cephalosporins can cause allergic reactions in approximately 5% to 10% of people with a penicillin allergy, although rates may be higher in some people. Allergic reactions to cephalosporins can be severe and even life-threatening.
If you have a penicillin allergy, you should talk with your healthcare provider about whether you also need to avoid cephalosporins.
Similarly, ask your allergist about whether it is safe to take imipenem, another beta-lactam antibiotic, if you have a history of penicillin allergy. Most patients with a true penicillin allergy will be able to tolerate imipenem, but depending on your history, a medically supervised graded-dose challenge or other precautions may be recommended.
People with penicillin allergy are also at higher risk of developing an allergy to a different class of drugs called sulfa drugs, which include antibiotics as well as other medications.
Managing a Penicillin Allergy When Medically Necessary
There may be certain cases when a person with a penicillin allergy needs penicillin or cephalosporin to manage an infection. In these situations, an allergist can perform skin testing and, if the test is negative, can try an oral challenge.
A desensitization process can also be performed in a hospital. This entails giving small amounts of the drug and gradually increasing doses over several hours until the person can tolerate a full therapeutic dose.
Keep in mind that desensitization is temporary. It only works if you are taking the drug at least every day. Once you stop, you’ll need to repeat the desensitization process.
Summary
Penicillin is one of the most commonly prescribed antibiotics. It is also the most common cause of drug allergy, along with comparable antibiotics such as cephalosporins. However, not everyone who reacts to penicillin has a true allergy.
A skin test can sometimes diagnose a true allergy, but a healthcare provider must do an oral challenge for an accurate diagnosis. There is no treatment for a penicillin allergy other than to avoid taking the medication.
A Word From Verywell
If you have any concerns about whether you are allergic to penicillin or a related drug, ask your healthcare provider about the possibility of being tested.
