Antibiotic allergy

With antibiotics being introduced early in childhood, it is common for patients to be mislabeled with an allergy to certain antibiotics. Penicillins, one of the most widely used class of antibiotics, are a group of antibacterial drugs sourced from the Penicillium mold. There are several antibiotics in the penicillin class, including Penicillin G, Amoxicillin, and Ampicillin. Given its frequent use, penicillin allergy remains the most commonly misreported drug allergy. Frequently, this misdiagnosis is due to inadequate or inappropriate allergy documentation, leading to the use of suboptimal second choice antibiotics.

In order to prevent these misdiagnoses and complications, it is important to differentiate between a side effect and an immune-mediated allergic reaction.

Side effects of penicillin 

Depending on the type of penicillin used, potential side effects/adverse effects include nausea, headache, diarrhea, vomiting, abdominal pain, and sore mouth. Other signs and symptoms of the infection being treated with antibiotics may also be mistaken for an allergic reaction.

Immune-mediated allergic reaction

An immune-mediated, type 1 allergic reaction is caused by your immune system becoming hypersensitive to the drug, mistaking the drug as a harmful substance. Once your immune system is exposed to the medication, it develops an antibody as a defense against it. The next time your body is exposed to the drug, these antibodies flag it as a harmful substance, causing your immune system to attack it. The chemicals released by your body during this process result in the signs and symptoms of an allergic reaction. 

Signs and symptoms of an allergic reaction to penicillins can occur within an hour and up to days after taking the drug. Symptoms include skin rash, hives, itching, fever, swelling, shortness of breath, wheezing, and anaphylaxis. Anaphylaxis is a rare, life-threatening systemic reaction that presents with symptoms of tightening of the airways and throat, dizziness, weak and rapid pulse, drop in blood pressure, and loss of consciousness. Any of these symptoms warrant seeking emergency medical help.  

Penicillin-related drugs

Penicillins belong to a class of antibiotics called beta-lactam antibiotics. Cephalosporins are another group of beta-lactam antibiotics that can cause similar reactions to penicillin, due to the chemical similarities. If you’ve had a previous allergic reaction to a type of penicillin, you may also be allergic to other types of penicillins or cephalosporins. Penicillins include Amoxicillin, Ampicillin, etc. Cephalosporins include Cefaclor, Cephalexin (Keflex), Cefadroxil. Although an allergy to penicillins does not imply an allergy to cephalosporins, it is important to be mindful of the increased likelihood. 

Risk factors

There are certain factors that can increase your susceptibility to developing an allergy to penicillins. A history of other allergies, such as food allergies or hay fever, make you a more allergic individual, therefore increasing the likelihood of having an allergy to drugs. Increased or prolonged exposure to penicillins can also increase your risk of developing an allergy to penicillins. It is important to remember that although some people may have an increased risk, anyone can develop an allergy to penicillins. It is also common to outgrow a penicillin allergy, especially if the diagnosis was given at a very young age. 

Diagnosis and treatment

If you carry the diagnosis of allergy to penicillin, it is important to clarify whether it is based on adverse reactions or a true allergy. Based on your previous reactions to penicillins, your allergist may recommend undergoing skin testing to penicillin. This involves a skin prick test, where different forms of penicillin are applied to the skin after a plastic applicator is used to break the surface. If the prick test is negative, the penicillins will be injected intradermally, just under the surface of the skin. If the intradermal test is also negative, an oral challenge of Amoxicillin will be given. If there are no immediate or delayed reactions, it will be determined that drugs within the penicillin class can be prescribed when medically indicated. In the event of a positive skin testing result, it would be recommended to avoid taking penicillins. 

If you suspect that you have an allergy to penicillin, it is important to clarify this allergy, as it can open up your options to more effective and appropriate antibiotic prescriptions.