Risks of Allergic Reaction to Penicillin: What You Need to Know

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Doctors prescribe penicillin or any of its cousins (the cephalosporin drugs) to treat bacterial infections. Once hailed as a “miracle drug,” penicillin helped reduce the severity of bacterial infections, beginning back in the 1940s, according to the American Chemical Society. Before the discovery of penicillin’s effects on infections, doctors had little to offer patients but hope.

In 1928, British doctor Alexander Fleming realized that a growth of mold on a petri dish had affected the growth of several bacteria colonies.

While penicillin and related antibiotics have helped to reduce unnecessary deaths from bacterial infections, some patients develop allergic reactions to this medication.

Body’s Reaction

An allergy to penicillin is defined as a reaction that takes place when your body’s immune system overreacts to the antibiotic. When you develop an allergic reaction to penicillin, you will experience the same symptoms with antibiotics that are related to penicillin.

Dangerous Allergic Reaction

Even though penicillin and its relatives are beneficial medications, killing bacterial infections, some people are severely allergic and develop a condition known as anaphylactic shock. This is the most dangerous penicillin allergy and it can be life-threatening.

If you are highly sensitive to penicillin, your reaction is immediate, with dizziness, difficulty breathing, wheezing, swelling of the tongue or throat, a drop in your blood pressure, rapid or weak pulse and a loss of consciousness. You may also develop diarrhea, nausea and vomiting, and your skin may develop a bluish color.

You are more likely to develop a severe allergic reaction if you suddenly develop hives after taking a dosage; if you have a positive skin test for penicillin or if you have had a previous anaphylactic reaction after taking penicillin, according to WebMD. This site points out that severe allergic reactions develop within an hour of taking the medication.

If you have had a dangerous, anaphylactic reaction to penicillin, your doctor can prescribe another antibiotic for your infection. You can also undergo desensitization therapy (an allergist gives you tiny amounts of the drug in injections and begins to gradually increase each dose until you no longer develop a severe reaction. You may need to undergo another desensitization session in the future because the effects are not permanent.

Allergic Reaction Symptoms

Milder allergic reactions include itchy eyes, hives, a rash and swollen lips, face or tongue. You may also develop wheezing.

A penicillin allergy develops when your body responds as if the medication is harmful; your immune system triggers cells to make immunoglobulin E, or IgE antibodies to fight the penicillin. Your system then produces chemicals that cause the physical signs you recognize as an “allergic reaction.” Even if your first reaction is a mild one, re-exposure to penicillin can trigger a more severe attack.

How You May Feel

You may feel the same as if you had been exposed to something like ragweed, plant pollen or animal dander. While you may not sneeze, your lungs feel the effect of the IgE antibodies, which leads to potential wheezing symptoms. Your skin and eyes also react because of the same IgE trigger.

Treatment for Mild Symptoms

Mild allergic reactions to penicillin or related antibiotics can be treated with an antihistamine like Benadryl. The antihistamine has to have diphenhydramine so it fights your body’s IgE response, which relieves the itchiness, swollen membranes and possible wheezing.

Treatment for Anaphylactic Reaction

If you develop a severe reaction or anaphylaxis, you will get a shot of epinephrine. Medical providers will give you epinephrine until your symptoms go away. If you are having a particularly severe reaction, medical providers can inject corticosteroids and antihistamines directly into your bloodstream –– intravenous treatment.


WebMD: Penicillin Allergy – Topic Overview - https://www.webmd.com/allergies/tc/penicillin-allergy-topic-overview

Mayo Clinic: Penicillin Allergy: Symptoms - https://www.mayoclinic.com/health/penicillin-allergy/DS00620/DSECTION=symptoms

ACS: Discovery of Penicillin - https://portal.acs.org:80/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=926&content_id=CTP_004451&use_sec=true&sec_url_var=region1&__uuid=b005c680-b4b6-43ad-893c-aa78523d46c3