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Intravenous benzathine benzylpenicillin added to oral phenoxymethylpenicillin for relief in adults with acute tonsillitis, peritonsillar phlegmon and abscess

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What is this trial about?

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

The study focuses on adults with acute tonsillitis, including complications such as peritonsillar phlegmon and peritonsillar abscess. These conditions involve infection and inflammation of the tonsils, with the latter two representing swelling or a pocket of pus around the tonsil. The intervention being tested is a single dose of benzylpenicillin given intravenously (through a vein) in addition to the usual oral penicillin pill. A matching placebo solution is used for comparison.

The purpose of the study is to determine whether the added intravenous dose speeds relief of symptoms compared with standard treatment alone. Participants are randomly assigned to receive either the study drug or the placebo, both in addition to the regular oral medication, and are followed for several weeks to record pain levels, use of pain‑relieving medicines, and any complications. After the initial treatment period, patients continue routine care and are observed for any further episodes or the need for surgery over the next months.

The research process

The trial runs in 10 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Study enrollment

    You sign the consent form and receive written information about the study procedures.

  2. Step 2

    Baseline assessment

    A study nurse records your medical history, current symptoms and performs the initial symptom score (STAT‑10 or PTAAT‑12) before any treatment is given.

  3. Step 3

    Randomization

    The study assigns you, in a hidden manner, to receive either the active medication or a placebo. you will not know which one you receive.

  4. Step 4

    Intravenous infusion

    You receive a single intravenous (through a vein) infusion. if you are in the active group, the infusion contains benzylpenicillin 1200 mg (1.2 g) dissolved in a solution. if you are in the placebo group, the infusion contains saline (sodium chloride) 1000 mg (approximately 1 liter of 0.9 % solution). the infusion is administered once, over a short period as directed by the study staff.

  5. Step 5

    Start oral antibiotic

    Immediately after the infusion you continue taking the standard oral antibiotic, phenoxymethylpenicillin, according to the dosage prescribed by your doctor. this medication is taken by mouth at regular intervals for the full course of treatment.

  6. Step 6

    Symptom recording on day 2

    On the second day after the infusion you complete the same symptom score (STAT‑10 for acute tonsillitis or PTAAT‑12 for peritonsillar conditions) to allow comparison with the baseline score.

  7. Step 7

    Pain medication tracking days 1–7

    You keep a simple diary of any pain‑relieving medicines you take from the first day through the seventh day. the total amount of analgesics used is recorded for the study.

  8. Step 8

    Check for complications up to day 14

    During the first two weeks you are asked to report any side effects, worsening of symptoms, or other health problems. the study team reviews these reports to assess safety.

  9. Step 9

    6‑month follow‑up

    Approximately six months after the start of the study you are asked to complete a quality‑of‑life questionnaire (TOI‑14) and to indicate whether you have needed a tonsillectomy or experienced new episodes of throat infection.

  10. Step 10

    12‑month follow‑up

    Around twelve months after enrollment you repeat the same questionnaire and report any additional throat infections or surgeries that have occurred during the year.

Who can join the trial?

6 criteria

  • Have an acute sore throat (acute tonsillitis) with a Centor score of 3‑4. The Centor score is a quick check that looks at four signs – fever, swollen neck glands, no cough, and white spots on the tonsils – to guess if the infection is caused by bacteria.
  • If you have a peritonsillar phlegmon (a swelling of tissue near the tonsil) and a Centor score of 3‑4, you are still eligible.
  • If you have a peritonsillar abscess (a pocket of pus near the tonsil) that is being treated by a small cut (incision) to drain it, you may join the study.
  • Be able to read and sign a written informed consent form, which shows you understand the study and agree to take part.
  • Be 18 years of age or older.
  • Both men and women are allowed to participate.

Who cannot join the trial?

3 criteria

  • If you have a known allergy or hypersensitivity (your body reacts badly) to penicillin (a common antibiotic), you cannot take part in the study.
  • If the infection has spread beyond the throat, you cannot join. This includes conditions such as a parapharyngeal abscess (a pocket of pus near the side of the throat), a retropharyngeal abscess (a pocket of pus behind the throat), necrotising fasciitis (a severe, fast‑moving infection that destroys tissue), mediastinitis (infection in the space in the chest between the lungs), or Lemierre’s syndrome (a rare infection that starts in the throat and spreads to neck veins).
  • If you are currently pregnant or planning to become pregnant, you cannot participate in the trial.
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Investigated drugs

  • benzylpenicillin

    is given as a single dose through an IV (a needle placed into a vein). In this study it is added to the usual treatment to see if it helps relieve pain and other symptoms faster for adults who have a sore throat, a peritonsillar infection, or an abscess.

  • phenoxymethylpenicillin

    is the regular oral (by mouth) antibiotic that patients normally take for these throat infections. In the trial everyone receives this standard medicine, and the researchers are testing whether adding the IV dose of benzylpenicillin provides extra benefit.

What is already known about the treatment

  • Benzathine benzylpenicillin

    This medication is given by a single intravenous injection, typically in a dose of about 1.2 g. It is an approved and widely used antibiotic that appears in medical guidelines and literature for treating bacterial infections. It is mainly used to help treat acute tonsillitis, peritonsillar phlegmon, and peritonsillar abscess. It works by attaching to proteins that build the bacterial cell wall, stopping the wall from forming and causing the bacteria to die; it belongs to the beta‑lactam penicillin class.

  • Sodium chloride

    The placebo is a 0.9 % sodium chloride solution that is injected into a vein as a sterile fluid. This isotonic saline is a standard, well‑known substance used in hospitals for fluid replacement and as a diluting agent. It has no therapeutic effect on the disease itself and is used only as a solvent in the trial. It simply provides water and salt to match the body’s natural balance and is classified as an electrolyte solution.

Investigated diseases

Tonsillitis - Tonsillitis is an inflammation of the palatine tonsils, usually caused by a viral or bacterial infection. It starts with a sore throat, redness, and swelling of the tonsils. In some cases the infection spreads behind the tonsil, producing a peritonsillar phlegmon, which is a localized area of swelling and pain. When the fluid collection becomes walled off, a peritonsillar abscess can develop, forming a pocket of pus. The condition progresses from mild throat discomfort to increasing difficulty swallowing and may be accompanied by ear pain or fever.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-526903-31-00Protocol code280526Estimated enrolment154 patientsSponsorRegion Midtjylland

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