the primary objective of this study is to assess and compare the efficacy, safety and benefits of Controlled Release (CR) oxycodone/paracetamol with our current pain protocol (paracetamol/naproxen) in the treatment of acute postoperative pain at home after painful day-case surgery. We hypothesize that ambulatory patients postoperatively treated with oxycodone/paracetamol will achieve better pain relief with equal side effects compared to patients treated with paracetamol/naproxen.

Our second goal is to assess analgesic adherence in the outpatient setting.

Endpoints:

Primary endpoints: pain intensity (Visual analogue scale) Secondary endpoints: - side-effects/ adverse effects of study medication

• patient satisfaction with pain treatment
• compliance to study medication

Study design:

Patients scheduled for painful ambulatory surgery (knee arthroscopy, unilateral open or laparoscopic inguinal hernia repair) will be enrolled in an open randomized controlled trial (RCT) at our pre-assessment clinic.

Subjects will be enrolled by a study nurse and will be randomized into one of three study treatment groups using a computer-generated list. Patients in group 1 (PCM/NAPR) are assigned to postoperative analgesia using naproxen 500 mg orally twice a day for 48 hours postoperatively. Patients assigned to group 2 (PCM/Oxy1) receive CR oxycodone 10 mg orally twice a day for 24 hours. Patients in group 3 (PCM/Oxy2) are postoperatively treated witch CR oxycodone 10 mg orally twice a day for 48 hours. All patients also receive paracetamol 1000 mg orally four times a day for 48 hours postoperatively.

Recovery after discharge will be assessed using a diary for up to 48 hours after surgery. Three times a day, patients have to rate pain at rest and movement (VAS), fatigue, nausea, vomiting, pruritus, miction problems, pyrosis, and abdominal complaints. Furthermore, compliance to the use of the study medication will be assessed by checking whether the patients took the study medication as prescribed and if any other pain medication was used. Compliance will be assessed three times a day and patients will be divided into three groups according to medication use: always = full compliance, sometimes = partial compliance, or never = no compliance.

Finally, overall satisfaction with the postoperative pain treatment will be assessed (score 0-10).

Inclusion Criteria:

• Patients scheduled for painful ambulatory surgery (knee arthroscopy, unilateral open or laparoscopic inguinal hernia repair)
• American Society of Anesthesiologists (ASA) physical classification I or II

Exclusion Criteria:

• cognitive impairment,
• preoperative pharmacologic pain treatment
• allergy to or a contraindication for taking the study medication (e.g. paracetamol, oxycodone, naproxen or another NSAID)
• porphyria
• pregnancy or lactation
• history of severe renal, hepatic, pulmonary, or cardiac failure
• current symptoms or history of gastrointestinal bleeding, ileus or chronic obstipation
• history of substance abuse, or use of medication with a suppressive effect on the central nervous system