11/09/2017

Allergic to penicillin? You may want to be tested for that.

Ninety percent of those who think they are allergic to penicillin are found not to be

Growing up were you told you had an allergy to penicillin? Has it made taking common medications and getting healthier sooner more difficult?

You may want to consider a penicillin allergy skin test. In 45 minutes or less, a St. Joseph’s/Candler pharmacist or nurse can determine if you are truly allergic.

Penicillin is an antibiotic discovered in the late 1940s. Today, penicillin is a group of antibiotics including penicillin G, penicillin V, procaine penicillin and benzathine penicillin. Penicillin or its derivatives are the most common antibiotics prescribed to inpatients at St. Joseph’s/Candler, says Bruce Jones, PharmD, BCPS, infectious diseases clinical pharmacy specialist. 

Bruce Jones, PharmD
Bruce Jones, PharmD, BCPS, infectious diseases clinical pharmacy specialist

Penicillin can be optimal drugs in that they have low side effects, many can be taken orally, and there are little drug interactions compared to other antibiotics, Jones says. The ability to take penicillin gives a patient access to more drugs that could have better outcomes, access to less expensive drugs, can decrease length of stays in the hospital and reduces the risk of infection.

A large population of the United States believes it has an allergy to penicillin when it does not, missing out on all the benefits of the antibiotic. According to research studies, 10 percent of the U.S. population, or 33 million people, say they are allergic to penicillin; however, 90 percent of those patients are not truly allergic or have lost that allergy over time.

“That’s almost 30 million Americans walking around saying, ‘I’m allergic to penicillin,’ and they really are not,” Jones says. “Just that claim of the penicillin allergy can completely take away that class and all those derivatives.”

An allergy occurs when someone is exposed to, in this case, penicillin and your body develops antibodies against it, Jones says. When your body is exposed again, you have an allergic reaction to it. Symptoms of a penicillin allergic reaction vary but may include rash, throat swelling or anaphylaxis.

“There are very serious reactions that can occur,” Jones says. “That’s why so many of these patients avoid it. If you have a reaction to penicillin, it is important to avoid it unless you are skin tested.”

Penicillin Allergy Testing

Because of the number of benefits to taking penicillin and the number of people not truly allergic, a penicillin allergy test can be performed on inpatients who claim the allergy. The skin test also is available in an outpatient setting at the Center for Infusion Therapy on the Candler Hospital campus.

The test is a three-step process; however, the third step is optional so for the majority of patients it’s only two steps, Jones says. It takes around 45 minutes to complete.

Step 1: Step one is a puncture, or scratch, test. There are four products used: saline, which is the negative control; histamine, which is the positive control; and two penicillin products, Pre-Pen and penicillin G. A drop of each is placed on your inner forearm via a syringe and then basically scratched into the skin. At this point, you wait 15 to 20 minutes and look for the histamine to be positive, which it always should be. A positive reaction is a raised wheel, or bump, two to three millimeters. What you hope to see, Jones says, is that the saline, Pre-Pen and penicillin G are negative. If, however, there is a positive reaction, or raised bump, to any of those remaining three products, the testing is over; the patient is still allergic. If all three of those are negative and the histamine is positive, you go on to step 2.

Step 2: Step 2 is an intradermal test, similar to a TB skin test, Jones says. The upper arm is often used as the site of testing. When the histamine is positive on the first step, it is no longer required for the second step. Small amounts of saline and the two penicillin products are injected under the top layer of the skin, creating a slightly raised bump. You wait another 15 or 20 minutes and hope to see completely negative results. If you see positive results, you stop and the patient is still allergic. A positive indication is a raised wheel at three millimeters or larger from the original blip.

Step 3: Step 3 is an oral ingestion challenge. This step is optional. It involves taking an amoxicillin tablet and reporting any symptoms. It is not required to declare the patient not allergic, and most inpatients are changed to a penicillin after a negative test anyway, Jones says.

“Anybody with a penicillin allergy would be a candidate for this test, but there are certain patients who are not candidates,” Jones says. “Anyone who has an allergy to penicillin has the option of being evaluated, and if they meet the criteria, can be tested.”

St. Joseph’s/Candler began penicillin allergy testing in August 2014. More than 250 inpatients at St. Joseph’s Hospital and Candler Hospital have since been tested, with approximately 20 outpatients tested at the Center for Infusion Therapy.  Jones personally has tested 193 patients and only three have tested positive.

“I think it shows you that we match up with what is nationally reported,” Jones says.

Jones would like to see more outpatients being tested and assures all patients that the test is safe and performed in a monitored environment by a trained, experienced staff.

If you are interested in the testing, Jones encourages you to talk to your primary care physician about the test and request an order for it. A referral is required to be tested at the St. Joseph’s/Candler Center for Infusion Therapy, located at Candler Hospital.

“Don’t wait until you are sick and really need it. Go ahead and find out now and know if you are truly allergic,” Jones advises. “The long-term implications of this are very big. It’s good to remove a penicillin allergy off anybody, but it’s great to remove one off someone that’s 20 years old. That’s 60, 70 years worth of antibiotics that they can get now that you have opened them up to penicillin.”

  • St. Joseph's Hospital Campus: 11705 Mercy Blvd., Savannah, GA 31419, (p) 912-819-4100
  • Candler Hospital Campus: 5353 Reynolds St., Savannah, GA 31405, (p) 912-819-6000
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St.Joseph's Hospital Campus: 912-819-4100

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