BackgroundPostoperative pain and, in a more extended perspective, quality of recovery (QOR) should be considered the principal endpoints after day surgery. Non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol are a cornerstone of pain treatment after painful day surgery. Nevertheless, NSAIDs are not always sufficiently effective, have numerous contraindications, and consequently are not suitable in up to 25 % of all patients. Metamizole is a non-opioid compound with a favourable gastrointestinal, cardiovascular and cerebrovascular profile compared to NSAIDs. The aim of this study is to assess if a combination of metamizole and paracetamol is non-inferior to a combination of ibuprofen and paracetamol in the treatment of acute postoperative pain at home after painful day case surgery. In addition, we aim to assess and compare quality of recovery (QOR) profiles of both groups.Methods/DesignThis is an investigator-initiated, double-blind, randomised controlled, non-inferiority trial. A total of 200 patients undergoing elective haemorrhoid surgery, arthroscopic shoulder or knee surgery, or inguinal hernia repair in a day care setting will be randomised to receive either a combination of metamizole and paracetamol (MP) or a combination of ibuprofen and paracetamol (IP). Participants will take study medication orally for 4 days. Primary endpoints are average postoperative pain intensity measured by an 11-point Numeric Rating Scale at postoperative day 1 and QOR profile measured by the Functional Recovery Index (FRI), the 1-item Global Surgical Recovery (GSR) index and the EuroQol (EQ-5D) questionnaire at days 1, 2, 3, 4, 7, 14 and 28 postoperatively. Secondary outcomes include compliance with study medication, adverse effects of study medication, use of rescue medication and satisfaction with study medication, surgery and hospital care and telephone follow-up.DiscussionThis study will provide clinical evidence on the analgesic efficacy and safety of a combination of metamizole and paracetamol in treating postoperative pain at home after painful day surgery. This study may also provide an insight into QOR profile after four different types of surgery and into the interrelationship between three different instruments used to assess QOR.Trial statusRecruitment is currently ongoing.Trial registrationEuropean Union Clinical Trials Register 2015-003987-35. Registered 10 November 2015.

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