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Metamizole Sodium Monohydrate vs Sodium Chloride for Post‑Operative Pain Relief in Adults Undergoing Elective Laparoscopic Cholecystectomy

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What is this trial about?

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

The study involves patients undergoing laparoscopic cholecystectomy (a minimally invasive surgery to remove the gallbladder) and focuses on managing postoperative pain (pain that occurs after the operation). The medication being tested is a single 1 g intravenous dose of metamizole (a pain‑relieving medication given through a vein) administered during the operation, compared with a placebo. All participants also receive the usual pain medicines paracetamol (a common over‑the‑counter pain reliever) and ibuprofen (a non‑steroidal anti‑inflammatory drug that reduces pain and swelling).

The purpose of the study is to determine whether adding intra‑operative metamizole reduces the amount of opioid (a strong pain‑relieving drug often used after surgery) needed in the first few hours after surgery. Participants are randomly assigned to receive either the study drug or placebo, remain unaware of which they received, and have their pain levels recorded regularly. The primary measure is the total morphine (measured as milligram equivalents, a standard way to compare the strength of different opioid doses) consumed during and for three hours after the operation, with additional observations of rescue pain medication use, time to discharge, and overall pain scores up to 48 hours.

The research process

The trial runs in 9 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial visit and consent

    After joining the study you will meet the study team for an initial visit. during this visit you will be asked to sign a consent form and to provide basic health information.

  2. Step 2

    Baseline assessment

    Your current pain level, medical history, and any medications you are taking will be recorded.

  3. Step 3

    Randomization

    The study will assign you to receive either metamizole 1 g or a placebo solution. you will not know which one you receive.

  4. Step 4

    Pre‑operative medication

    You will receive the standard pain‑relief regimen that includes paracetamol and ibuprofen as directed by the surgical team.

  5. Step 5

    Administration of study drug

    During the operation a single intravenous dose of 1 g metamizole (or 1 g sodium chloride placebo) will be given. the injection is given directly into a vein.

  6. Step 6

    Surgery

    The laparoscopic cholecystectomy procedure will be performed while you are under anesthesia.

  7. Step 7

    Post‑operative monitoring

    After surgery you will be taken to the recovery area. your pain level (pain score) will be measured every 15 minutes for the first hour (at 0, 15, 30, 45, and 60 minutes).

    Any additional pain relief (rescue analgesia) will be given if needed, and the amount of opioid medication used will be recorded for the first three postoperative hours.

  8. Step 8

    Discharge assessment

    You will be evaluated with the alderte score and the padss to determine when you are ready for discharge from the day‑care unit.

  9. Step 9

    Post‑operative follow‑up

    Pain levels and any pain medication you take will be recorded for up to 48 hours after the operation.

    On postoperative day 1 and day 2 you will complete a quality‑of‑recovery questionnaire (qor-15).

Who can join the trial?

6 criteria

  • You must sign a written form showing you agree to join the study; this is called informed consent.
  • You need to be healthy enough for same‑day surgery, which is measured by an ASA score of 1, 2, or 3 (a rating of how well your body can handle the operation).
  • You must be between 18 and 75 years old.
  • You must be scheduled for a planned (elective) minimally invasive gallbladder removal, called a laparoscopic cholecystectomy, done in a day‑surgery clinic.
  • You need to be able to speak Dutch.
  • You must weigh at least 53 kilograms (about 117 pounds).

Who cannot join the trial?

13 criteria

  • Cannot join if you have ever had an allergy or intolerance to any drug used for general anesthesia (the medicines that make you sleep during surgery).
  • Cannot join if you are allergic to pyrazolones/pyrazolidines (a group of pain‑relief medicines) or have had severe breathing problems (bronchospasm) or a strong allergic reaction (anaphylactoid reaction) to common pain relievers such as aspirin, paracetamol, diclofenac, ibuprofen, indometacin or naproxen.
  • Cannot join if you have acute intermittent hepatic porphyria, a rare liver disorder that can cause severe pain and other serious symptoms.
  • Cannot join if you have a known glucose‑6‑phosphate dehydrogenase (G6PD) deficiency, an inherited condition that can cause red blood cells to break down under certain stresses.
  • Cannot join if you have low blood pressure (hypotension) or unstable circulation (hemodynamically unstable) before the operation.
  • Cannot join if you are allergic or intolerant to the study drug itself, called the investigational medicinal product (IMP).
  • Cannot join if you received chemotherapy (cancer treatment) within the past two years.
  • Cannot join if you have a history of, or currently have, very low white‑blood‑cell counts (agranulocytosis) or any other blood disease (hematological disorders).
  • Cannot join if you have or have had ulcers or bleeding in the stomach or the first part of the small intestine (gastric/duodenal ulceration).
  • Cannot join if you regularly take strong pain medicines (opioids), antidepressants, or long‑term anti‑inflammatory drugs (NSAIDs).
  • Cannot join if your body mass index (BMI) is greater than 35 kg/m² (a measurement that indicates obesity).
  • Cannot join if the doctor believes you have any other health condition that could make the study unsafe for you or affect the study results.
  • Cannot join if you are a woman who is pregnant, breastfeeding, planning to become pregnant, or could become pregnant and are not using a reliable, highly effective birth‑control method.
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Investigated drugs

  • Metamizole

    is a strong pain‑relieving medicine that is given through a vein during the operation. In this trial it is added to the usual pain‑control plan to see if it can lower the amount of opioid pain medicines that patients need right after their gallbladder surgery.

  • Paracetamol

    is a common over‑the‑counter drug that reduces pain and fever. In the study it is part of the regular pain‑relief regimen given before and after the surgery to help keep patients comfortable.

  • Ibuprofen

    is a non‑steroidal anti‑inflammatory drug that eases pain and reduces swelling. It is also included in the standard pain‑control plan for the patients undergoing the laparoscopic gallbladder operation.

What is already known about the treatment

  • Metamizole sodium

    This medication is given as a 1 g dose in a sterile liquid that is injected directly into a vein (IV injection or infusion). It is an approved pain reliever in many countries and is described in medical literature as a non‑opioid analgesic, though some regions have limited its use because of rare blood‑cell side effects. It is mainly used to treat moderate to severe pain after surgery, such as the pain following laparoscopic cholecystectomy. Metamizole works by reducing the production of prostaglandins and acting on pain pathways in the brain, and it belongs to the pyrazolone class of non‑opioid analgesics.

  • Sodium chloride

    This product is a sterile 0.9 % saline solution that is administered intravenously as a simple fluid infusion. It is a standard medical solution that is widely documented and used worldwide as a basic electrolyte and fluid replacement. Its primary role is to provide sodium and chloride ions to maintain fluid balance and to serve as a harmless carrier for other medicines in clinical trials. Sodium chloride is classified as an electrolyte solution and a diluting agent.

Investigated diseases

Postoperative pain - Postoperative pain is the discomfort that arises after a surgical operation. It typically begins shortly after the procedure and is most intense during the first few hours. The intensity usually decreases over the first days as the surgical site heals. Pain may be localized to the incision area and can spread to surrounding tissues. In most patients the pain resolves completely within a week to ten days as tissue repair progresses.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase ITrial ID2026-526531-18-00Estimated enrolment76 patientsSponsorUZ Leuven

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