NEFARTHRO is a multicentric randomized controlled trial comparing the effects of discontinuous infusions of nefopam (bolus) versus continuous infusion of intravenous nefopam (via an infusion pump) versus placebo on the opioid-request during the first 24 hours following a Total Hip arthroplasty, as part of multimodal analgesia including at least paracetamol and a Non-Steroidal Anti-Inflammatory Drug (NSAID).

The primary endpoint is cumulative morphine consumption for the first postoperative 24 hours, expressed in mg of iv equivalent morphine, including titration in the Post Anesthesia Care Unit (PACU).

Patients will be followed during 6 months.

Inclusion Criteria:

• Patient aged ≥ 18 years, fluent in French.
• Planned primary or secondary total hip replacement, regardless of surgical approach or type of prosthesis.
• Receiving paracetamol and ketoprofen postoperatively.
• Under general anesthesia or spinal anesthesia (without intrathecal morphine).
• Participant affiliated to a social security scheme
• Participant's free, informed and written consent

Exclusion Criteria:

• Septic or carcinological surgery
• Allergy to paracetamol, nefopam or NSAIDs
• Angle-closure glaucoma
• Prostate adenoma
• history of convulsion
• Nocturnal pollakiuria in men with more than two risings per night
• Severe hepatic (Child C) or cardiac insufficiency (LVEF < 30%)
• Renal insufficiency with creatinine clearance < 50 mL/ min according to Cockroft's formula
• Active peptic ulcer or history of digestive bleeding or peptic perforation
• Patients with opioid treatment for chronic pain other than coxarthrosis (fentanyl, oral morphine > 50mg/d or equivalent)
• Protected patient: safeguard of justice, guardianship or curatorship
• Incomprehension or inability to use a numerical rating scale or to self-assess/manage pain
• Pregnancy or breast-feeding

Patient, investigator and outcome assessor will be blind., A nurse anesthetist who will not be involved in the follow up of the patient will receive the kit and prepare the syringes.