The aim of the study is to assess the effectiveness and tolerance of pain treatment in AP in children using intravenous paracetamol in combination with ibuprofen or paracetamol in combination with metamizole. The study is prospective, interventional, and randomized.

Patients with AP diagnosed based on the INSPIRE criteria who meet the inclusion as mentioned above criteria for the study will be randomized (based on a computer-generated randomization list, in blocks of four people) to treatment with one of two regimens:

Group A will receive a dose of paracetamol intravenously 15 mg/kg body weight (maximum 1000 mg/dose) and ibuprofen 10 mg/kg body weight (maximum 400 mg/dose).

Group B will receive a dose of paracetamol intravenously 15 mg/kg body weight (maximum 1000 mg/dose) and metamizole 15 mg/kg body weight (maximum 100 mg/dose).

The initial pain assessment will be carried out according to pain assessment scales in children adapted to the patient's age and cognitive abilities (NRS, Wong-Baker Faces Scale/FLACC- attached). The effectiveness of the treatment will be assessed 60 minutes after the start of the intervention.

Before starting the intervention, all patients during obtaining peripheral intravenous access will undergo a panel of laboratory tests including: alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase activity, total, conjugated and unconjugated bilirubin level, peripheral blood morphology, C-reactive protein, glucose, creatinine, calcium, albumin and urea nitrogen level. Oral and/or intravenous fluid supply in the range of 1.5 to 2 times the daily requirement will be provided, as well as early low-fat enteral nutrition.

After the intervention is completed, the decision on further analgesic treatment will remain at the discretion of the attending physician.

In addition, during the examination, data about the patient will be collected, such as: age, gender, body weight, height, history of chronic diseases and congenital defects, medications taken, reported allergies and family history, with particular emphasis on pancreatic diseases, as well as the results of laboratory tests and imaging, as well as data on possible side effects of the treatment. The patient will be observed for 48 hours from the start of the intervention.

Inclusion Criteria:

• diagnosis of AP according to the INSPPIRE mentioned above criteria,
• age from 3 to 18 years of age,
• abdominal pain on admission assessed on the Numerical Rating Scale (NRS) or FLACC >= 4 points,
• no analgesic treatment before enrolment in the study OR the last dose of analgesic drug (paracetamol, ibuprofen, metamizole) taken ≥ 6 hours before enrolment for examination,
• consent of legal guardians and the child (in the case of patients ≥16 years of age) to participate in the study.

Exclusion Criteria - patients:

• who took the last dose of painkiller (paracetamol, ibuprofen, metamizole) < 6 hours before entering the study,
• allergic to acetylsalicylic acid, other NSAIDs, paracetamol, metamizole,
• with inflammatory bowel disease,
• with gastrointestinal bleeding and other active bleeding,
• with gastric and/or duodenal ulcer disease,
• chronically taking paracetamol, NSAIDs, metamizole,
• with liver failure,
• with heart failure according to the NYHA II-IV scale,
• with acute and chronic renal failure,
• with cancer,
• whose legal guardians did not consent to participate in the study,
• who did not consent to participate in the study (applies to patients > 16 years of age).