Penicillin, Amoxicillin and Cephalosporin Allergy

Allergy to Beta Lactam Antibiotics

Mother Giving Penicillin Medicine to His Sick baby Boy
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Penicillin is perhaps the most well-known member of a group of antibiotics called beta-lactams, which refers to a particular structure in their chemical makeup. The structure is also shared by semi-synthetic penicillin (amoxicillin), cephalosporins, and other antibiotics (such as imipenem). Penicillins and cephalosporins are the most commonly used antibiotics to treat common infections.

Penicillins and cephalosporins are also the most common causes of drug allergy. About 10% of Americans report an allergy to penicillin or a related antibiotic. While penicillin allergy most commonly occurs in young adults, reactions can occur at any age. Women appear to be at higher risk than men. Approximately 300 deaths can be attributed to penicillin allergy each year in the United States. Symptoms of an allergic reaction to penicillin may include anaphylaxis, hives, below-the-skin swelling, asthma symptoms, as well as non-allergic symptoms such as serum sickness, certain forms of anemia, and other drug rashes.

How is Penicillin Allergy Diagnosed?

While many people report having an allergy to penicillin, less than 10% of these actually have a true allergy to the drug. Skin testing is the best method for diagnosing a penicillin allergy. However, the commercially available extract for penicillin skin testing was removed from the market in 2004, due to manufacturing problems. This extract, called Pre-Pen, once again became available in 2009. Alternatively, a RAST (blood test) for penicillin is available. Unfortunately, a negative RAST result does not exclude the possibility of penicillin allergy.

How is Penicillin Allergy Treated?

Other than the immediate treatment of drug allergy symptoms, the main treatment for penicillin allergy is avoidance of future use of penicillin and related antibiotics.

Cephalosporins can cause allergic reactions in people with penicillin allergy. The overall rate of allergy to cephalosporins in people with penicillin allergy is approximately 5 to 10%, although rates may be higher for certain people. Allergic reactions to cephalosporins can be severe and even life-threatening; it is generally recommended that those allergic to penicillin avoid cephalosporins altogether.

There may be certain cases, however, when a person with a history of penicillin allergy absolutely needs penicillin or cephalosporin. In these situations, an allergist can perform skin testing and, if negative, give the patient a small amount of the drug under close monitoring to determine how much--if any--he can tolerate (known as an oral challenge.) If a person who is truly allergic to penicillin has an infection that requires treatment with penicillin, a desensitization process can be performed in a hospital. This entails giving initially small amounts of the drug and gradually increasing doses over a number of hours until the person can tolerate a full therapeutic dose.

What Other Medications Should a Person With Penicillin Allergy Avoid?

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-“

Imipenem may also cause allergic reactions in people with penicillin allergy and should be avoided.

Want to keep learning? People with penicillin allergy are at higher risk of developing an allergy to sulfa antibiotics. Learn about sulfa allergy.

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