An allergic reaction is when your immune system mistakenly thinks the drug is a harmful substance. After an initial exposure to the drug, your body develops antibodies to the substance. When re-exposed, chemicals flood the body which causes the signs and symptoms of an allergic reaction. For the vast majority of cases, an allergic reaction to penicillin will occur within an hour of taking the drug. However, sometimes the reactions can manifest as much as several weeks after exposure.
Although rare, anaphylaxis is the most serious allergic reaction that can occur. If you or a loved one has taken penicillin and exhibits any kind of difficulty breathing, you need to call an ambulance or get them to an emergency room as quickly as possible. There are several paths for doctors to take when diagnosing penicillin allergies. The best course is a combination of three methods: history and physical exam, a skin test, and a challenge dose.
During a history and physical exam, your doctor should ask some crucial questions to help them understand the nature of the reaction such as the specific medication s you were taking when the reaction occurred, what type of reaction occurred, how long into the course did the reaction start, how long did the reaction last, how did you treat the reaction, and what was the final outcome.
If your doctor doubts a penicillin allergy after this examination, they may recommend further testing and refer you to an allergist for allergy testing. An allergy skin test usually involves putting a small amount of the suspected allergen penicillin on the skin of your arm and waiting to see if a small skin reaction occurs. The allergist will typically use a toothpick-like tool called a stylet to apply the substance to the test area.
Within about 15 minutes of applying the test, a raised bump resembling a mosquito bite will appear on the skin if you are truly allergic to penicillin. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Top of the page. Topic Overview What is penicillin allergy? What are the symptoms of penicillin allergy? What makes you more likely to have a severe allergic reaction to penicillin?
You may be more likely to have this type of reaction if you have had: A positive skin test for penicillin allergy. Hives that appeared quickly after you took the penicillin. A previous anaphylactic reaction to penicillin. Is penicillin allergy common? How is an allergic reaction to penicillin treated? Related Information Drug Allergies. Credits Current as of: June 29, Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
This content does not have an English version. This content does not have an Arabic version. Overview Penicillin allergy is an abnormal reaction of your immune system to the antibiotic drug penicillin. Drug rash Open pop-up dialog box Close. Drug rash A drug rash usually starts within two weeks of taking a new medication and begins as discrete red spots that spread, covering large areas of the body.
Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Show references Shenoy ES, et al. Evaluation and management of penicillin allergy. Journal of the American Medical Association. Accessed Oct. Drug allergies. Kufel WD, et al. Read the transcript of the conversation.
Listen to expert Kimberly G. This information packed episode is useful for patients, the general public and medical professionals. February 10, Penicillin Allergy — what do you need to know? Share this page:.
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