The goal of the ATX101-TKA-004 clinical trial aims to evaluate the efficacy and safety of ATX101 1,500 mg in participants undergoing primary unilateral total knee arthroplasty. The study will compare the effectiveness of ATX101 with a saline placebo and bupivacaine, an active comparator. Additionally, it will assess opioid consumption among participants receiving ATX101 versus those given the saline placebo and bupivacaine. The trial will also focus on the safety and tolerability of ATX101 in the participants.

Key Inclusion Criteria:

• Primary indication of TKA is knee pain due to osteoarthritis or post-traumatic arthritis
• Scheduled to undergo primary unilateral TKA with a cemented prosthesis, without use of a surgical drain, and under bupivacaine spinal anesthesia (dextrose is permitted)
• American Society of Anesthesiology (ASA) Physical Classification System of class 1, 2, or 3
• Capable, able, and willing to comply with all trial visits and procedures. Participant must also be able to use trial required e-diary and demonstrate completion compliance during the screening period
• English or Spanish speaking, willing, and capable of providing written informed consent

Key Exclusion Criteria:

• Has a planned concurrent surgical procedure (e.g. bilateral TKA) at the time of surgery or a planned surgical procedure before the last trial visit
• Has had any previous open surgery, (e.g., ORIF for fracture, osteotomy, arthroplasty, unicompartmental knee arthroplasty, or TKA), in the trial knee at any time in the past or arthroscopic surgery within 12 months. Has had any previous surgery in the contralateral knee within 6 months prior to screening
• Has been administered any type of intra-articular injection within 3 months of surgery in the trial knee
• Unable to abstain from opioid use for knee pain (including codeine) within 2 weeks (14 days) of surgery
• Has a Body Mass Index (BMI) ≥45 kg/m²
• Is unwilling or unable to discontinue use of medications or products that can impact pain control from the Screening Visit until the last trial visit (e.g. cannabidiol (CBD) oil, Kratom)
• Has a medical condition or receiving medication such that, in the opinion of the Investigator, participating in the trial would pose a health risk to the participant or confound the postsurgical assessments or might confound or interfere with the outcome of the trial
• Has received/used an investigational drug, product, or device for a clinical trial within 30 days of screening. COVID-19 vaccines (approved or under emergency use authorization locally) are permitted if the participant is not in a clinical trial for the vaccine
• Has a positive drug screen at the Screening Visit or on the day of surgery
• Has participated in an ATX101 clinical trial
• Pregnant, breastfeeding, or planning to become pregnant during the trial or before the last trial visit

Other protocol defined Inclusion/Exclusion criteria may apply

surgical staff and pharmacist dispensing assigned treatment will not be blinded to the trial treatment