Patients experience pain after their knee replacement surgery - and some may continue to experience persistent pain long after their knee replacement surgery. Traditional pain management strategies reply on pain medication such as opioids for pain control. However, these drugs do not work well for pain associated with movement or the the nerve pain (tingling, electrical sensations) after surgery. In addition, opioids are associated with significant side effects such as nausea, vomiting, respiratory depression, depression, cognitive dysfunction and risk of persistent opioid use. Neuropathic pain medications, such as venlafaxine are effective in managing nerve pain. Recent studies also support its potential role in acute pain management. Here, we propose a prospective randomized clinical trial 1) to evaluate the efficacy of Venlafaxine in reducing pain intensity and opioid consumption at post-operative day 1 (POD1) and 1- week after surgery, and 2) to examine whether the use of Venlafaxine will reduce the incidents of chronic postsurgical pain in TKA patients at 3-month time point.

Patients meeting the inclusion criteria will be randomized to receive either Venlafaxine extended release (ER) 37.5 mg/d or a placebo on the day of surgery and continue the treatment for 7 days after surgery. The primary outcomes include pain severity score (numeric rating scale, NRS) and consumption of morphine miligram equivalent (MME) at 24 hours. The secondary outcome will measure MME and NRS at postoperative day 7. In addition, the disability scale and perceived function 3 months after surgery will be compared to the baseline level by using PROMIS (Patient-Reported Outcomes Measurement Information System)10 Global Health, KOOS, JR. (Knee injury and Osteoarthritis Outcome Score Short Form), and VR-12 (Veterans RAND 12 Item Health Survey) Scale.

Inclusion Criteria:

• adult (male and female) subjects aged 18 to 75,
• English speaking,
• are scheduled for primary total knee arthroplasty with planned spinal anesthesia with saphenous peripheral nerve block at the adductor canal.

Exclusion Criteria:

• general anesthesia,
• hepatic & renal failure,
• history of diabetic peripheral neuropathic pain,
• chronic opioid use,
• concurrent use of antidepressants, triptans, and/or linezolid,
• allergy to the study medications,
• prior knee surgery,
• BMI > 40,
• bleeding disorders,
• history of recent falls,
• concurrent benzodiazepine use.

We will share our raw clinical data with other researchers.

For the entire study period

Non-profit and research purpose.