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A Study Testing Prolonged versus Single Dose Penicillin Challenge in Patients with Suspected Penicillin Allergy Using Amoxicillin

Verified siteInvestigationalNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study focuses on penicillin allergy, which is a type of allergic reaction that some people experience when taking penicillin antibiotics. People who have a history of penicillin allergy are often referred to allergy clinics to determine if they truly have an immune system reaction to this medication. The study will use amoxicillin, which is a type of penicillin antibiotic, and compare it to placebo. The purpose of the study is to find out whether giving amoxicillin for five days is better than giving it as a single dose for determining if someone has a true immune-mediated allergy to penicillin.

Participants in this study will be people who have a history of delayed allergic reactions to penicillin, meaning their symptoms appeared more than six hours after taking the medication, or people who are unsure about when their reaction occurred. All participants will first receive a single test dose of amoxicillin. Those who tolerate this first dose without problems will then be randomly assigned to receive either amoxicillin capsules or placebo capsules for five days. Neither the participants nor the doctors will know which treatment each person is receiving during the study.

The study will monitor participants for any allergic reactions that occur up to seven days after the first test dose, with additional monitoring continuing up to fourteen days. Participants will have follow-up appointments either through telehealth or in person at the clinic. An independent panel of experts who do not know which treatment participants received will review any reactions to determine if they are truly immune-mediated allergic reactions. The study will also measure how the testing affects participants' quality of life using a questionnaire at the beginning of the study and again at ninety days.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial challenge dose

    After joining the study, you will receive a first test dose of amoxicillin by mouth. Amoxicillin is a type of penicillin antibiotic.

    This first dose will be given to confirm that you can tolerate the medication without an immediate reaction.

    You will be observed during this initial dose administration.

  2. Step 2

    Assignment to treatment group

    After tolerating the first dose, you will be assigned to one of two groups. Neither you nor your doctor will know which group you are in.

    One group will receive amoxicillin capsules to take for 5 days.

    The other group will receive placebo capsules, which contain no active medication, also for 5 days.

    The capsules will be taken by mouth.

  3. Step 3

    Taking the study medication

    You will take the assigned capsules for 5 days.

    The specific dosage and frequency of administration will be provided to you by the study team.

    You should follow the instructions carefully during this period.

  4. Step 4

    Monitoring period up to day 7

    You will be monitored for any allergic reactions from the time you take the first test dose up to and including day 7.

    This monitoring will help determine if you have a true immune-mediated allergy to penicillin.

    Any reactions that occur during this time will be reviewed by independent doctors who do not know which treatment group you were assigned to.

  5. Step 5

    Follow-up review

    You will have a follow-up review after completing the challenge. This can be done either through a video call or in person at the clinic.

    During this review, your condition and any reactions will be assessed.

  6. Step 6

    Extended monitoring period up to day 14

    You will continue to be monitored for any delayed allergic reactions up to and including day 14 after the first test dose.

    Any reactions during this extended period will also be evaluated by the independent review panel.

  7. Step 7

    Quality of life assessment at day 90

    At day 90, you will be asked to complete a questionnaire about your quality of life related to drug allergies.

    This questionnaire will be compared to one you completed at the beginning of the study to assess any changes.

Who can join the trial?

6 criteria

  • You must be an adult patient who has been referred to an allergy clinic, which is a special clinic where doctors check if you have allergies, because you have a history of being allergic to penicillin, a common type of antibiotic medicine used to treat infections
  • Your allergy to penicillin must be of a type called immune-mediated, which means your body's defense system reacts to the medicine, and your reaction must have happened more than 6 hours after taking the medicine, or you do not remember when the reaction happened
  • You must have already taken the first dose of a test medicine called amoxicillin, which is similar to penicillin, without having a bad reaction to it
  • You must be willing and able to agree to take part in the study by giving your consent, which means your permission
  • You must be willing and able to have follow-up visits with the doctor either by video or phone call, called telehealth, or by visiting the clinic in person after taking the test medicine
  • If you are not currently in the hospital, you must not be taking or planning to take any antibiotic medicines from the beta-lactam group, which includes penicillin and similar antibiotics, during the 14 days of the study

Who cannot join the trial?

9 criteria

  • You have had a severe allergic reaction to penicillin in the past, such as trouble breathing, swelling of the face or throat, or a serious skin reaction
  • You have had a recent infection that required treatment within the last few weeks
  • You are currently taking medications that might interfere with the study
  • You have a condition that affects your immune system, which is the body's natural defense against illness
  • You are pregnant or breastfeeding
  • You have severe heart, kidney, or liver disease
  • You have had an allergic reaction to multiple different antibiotics in the past
  • You are unable to take medications by mouth
  • You have a condition that makes it unsafe for you to be exposed to penicillin
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Investigated drugs

  • Penicillin

    is an antibiotic medication used to treat bacterial infections. In this study, it is being given orally (by mouth) to test whether patients have a true allergy to penicillin. The study compares giving penicillin for 5 days versus giving it as a single dose to see which method is better at determining if someone is truly allergic to this antibiotic.

  • Placebo

    is an inactive substance that looks like the real medication but contains no active medicine. It is used in this study to compare against penicillin to help researchers understand the true effects of the antibiotic.

What is already known about the treatment

Penicillin – Penicillin is an antibiotic medication that is typically taken by mouth or given by injection and works by stopping bacteria from building their protective cell walls, which causes the bacteria to die. In this clinical trial, penicillin is being used in an oral challenge test to determine whether patients truly have an immune-mediated allergic reaction to penicillin or if their allergy label is incorrect. The study compares giving penicillin for five consecutive days versus a single dose to see which method is better at identifying real penicillin allergies. This research is important because many people are labeled as penicillin-allergic when they may not actually be allergic, which can limit their treatment options.

Investigated diseases

Penicillin Allergy – Penicillin allergy is an abnormal reaction of the immune system to penicillin antibiotics. When a person with this allergy takes penicillin, their body mistakenly identifies the medication as a harmful substance and triggers an immune response. The allergic reaction can occur immediately after taking the medication or develop over several days. Symptoms may include skin rashes, hives, itching, fever, or swelling. The severity of reactions can vary from mild skin symptoms to more serious responses involving multiple body systems. This condition is immune-mediated, meaning it involves the body's defense system responding inappropriately to the antibiotic.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-520888-41-00Estimated enrolment712 patientsSponsorAustin Health

sourced from the EU Clinical Trials Register and site verification

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).