Nefopam is a benzoxazocine derivative which is non-opioid and non NSAIDs. The previous studies showed that nefopam can inhibit reuptake of serotonin, norepinephrine and dopamine. It has no respiratory depression so may be useful in potential airway compromized surgery like anterior cervical discectomy and fusion (ACDF). This study aims to study the analgesic properties of nefopam after ACDF.

The investigators enroll 50 patient who admitted for ACDF. Standard general anesthesia will be performed in all of the patients. Then, an hour before finishing operation, the patients will be divided into two groups. The first group will receive Nefopam 20 mg infuse for 60 min. The another group or group NSS will receive the same amount of 0.9% sodium chloride. The recorded data include patient demographic data, intraoperative blood loss, hemodynamics and pre and postoperative pain scores and Thai version of the Neuropathic Pain Symptom Inventory (NPSI-T score).

Inclusion Criteria:

• Patients with cervical spondylosis or cervical spondylotic myelopathy undergoing elective anterior cervical spine surgery such as ACDF or anterior cervical corpectomy and fusion (ACCF)
• American Society of Anesthesiologists (ASA) class I-III
• Age 18-75 years old
• Body weight > 50 kg, BMI < 30 kg/m2

Exclusion Criteria:

• Convulsion or seizure
• Myocardial ischemia or infarction
• Risk of urinary retention from urethral disease or prostate disease
• Angle closure glaucoma
• Patients on monoamine oxidase inhibitor
• Psychiatric patients
• Pregnant or lactated woman
• Creatinine clearance < 30 ml/min
• Allergic to nefopam
• Patients on pregabaline or gabapentin
• Poorly controlled hypertension
• Cannot understand or do the questionnaire of Thai version of Neuropathic pain symptom inventory (NPSI-T) score