Study to Evaluate Safety/Efficacy of a Single Pre-Op Dose of AYX1 Injection to Treat Pain After Knee Replacement Surgery

The objectives of this study are to evaluate the safety and analgesic efficacy of a single preoperative intrathecal administration of AYX1 Injection at two dose/volume levels.


Eligibility Criteria:
Inclusion Criteria:

* Scheduled to undergo primary unilateral TKA for painful osteoarthritis without congenital knee pathology
* American Society of Anesthesiologists Physical Status Classification System ≤ 3
* Medically stable as determined by the Investigator based on pre-study medical history, physical/neurological examination, clinical laboratory tests, and 12-lead electrocardiogram (ECG) findings
* Body Mass Index of 18-40 kg/m2
* Stable medical regimen for at least 1 month before randomization
* Able to read and understand study instructions in English, and willing and able to comply with all study procedures

Exclusion Criteria:

* More than 2 other current focal areas of pain, none greater in intensity than the target knee and no other active chronic pain conditions that would compromise operative knee pain evaluation
* Inflammatory arthridities (e.g., rheumatoid arthritis, lupus, ankylosing spondylitis, psoriatic arthritis), with the exception of clinically stable/non-active gout that does not affect the knee and does not interfere with walking
* Operative arthroscopy in the surgical knee in the last 4 months (except for meniscal repair which will be no shorter than 6 months before randomization) or in the contralateral knee in the last 2 months (or 3 months for meniscal repair), or other prior surgery in either knee in the last 12 months, except for diagnostic arthroscopy
* Planned use of any of the following for TKA: general anesthesia using potent inhalational agents, peripheral nerve block (i.e., femoral nerve block), neuroaxial (intrathecal or epidural) opioids postoperatively, or knee capsule injections
* Received aspirin or any nonsteroidal anti-inflammatory drug (NSAID) prior to randomization within the washout period required by the surgical team for surgery with spinal anesthetic, or planned use of NSAIDS post-operatively through Day 28
* Use of more than 20 mg per day (on average) of oral morphine or its equivalent within 1 month prior to randomization
* Use of adjuvant analgesics for chronic pain control (e.g., gabapentin, pregabalin) within 2 weeks prior to randomization or planned use post-operatively through Day 28
* Daily use of benzodiazepines in the 3 months prior to randomization (unless used for sleep and dosage will be consistent after surgery)
* Use of systemic corticosteroids (does not include inhaled steroids) within 3 months or intra-articular steroid injections within 1 month prior to randomization, or planned use of either post-operatively through Day 28
* Treatment with immunosuppressives, antipsychotics, anticholinergics, or anticonvulsants within 1 month of randomization, with the exception of aspirin for cardiac prophylaxis (as long as discontinued within 1 week of randomization)
* Current neurologic disorder, which could confound the assessment of pain (e.g., Parkinson's, Multiple Sclerosis)
* Current active depression symptoms
* Has had a change in dose or regimen of SSRIs or SNRIs for depression within 1 month of randomization
* Mini Mental State Exam score \< 24 at Screening
* Severe pulmonary disease; if symptomatic sleep apnea is currently treated with continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BIPAP), use must be continued postoperatively at least during the inpatient period. Patients with sleep apnea associated with a history of postoperative delirium are excluded.
* Current evidence of alcohol abuse or history of alcohol-related complications within 1 year of randomization including, but not limited to, alcoholic withdrawal seizures, hallucinations, delirium tremens or detoxification treatment
* Known or suspected history of illicit drug abuse within 1 year before randomization, current or planned use of medical marijuana, or history of opioid dependence within 2 years before randomization
* Any malignancy within the past year, with the exception of basal cell carcinoma or uncomplicated or stable skin cancers documented to not require further or immediate treatment
* Women who are pregnant or nursing
* Previous participation in any study involving AYX1 Injection