for people ages 40-90 (full criteria)
at La Jolla, California and other locations
study started
completion around



The primary objective of this study is to evaluate the safety and efficacy of CNTX-6970 for the treatment of pain related to OA of the knee compared to placebo. CNTX-6970 is being developed as a new treatment for chronic pain, including painful osteoarthritis of the knee.

Official Title

EN20-01: A 24 Week Study to Evaluate the Safety and Efficacy of CNTX-6970 in Subjects With Moderate to Severe Knee Osteoarthritis Pain.


The study will employ a randomized, allocation-concealed, multicenter, placebo-controlled, multi-period crossover design (Schmid et al, 2018). This multi-period crossover randomized, controlled trial allows comparability and assessment of efficacy through repeated exposures within each subject to the active treatment and a control (placebo) in randomized sequence. Such multi-period crossover designs are ideal for treatments with rapid onset of action and short half-life such as the asset under study here. We have strived to minimize the complexity of this powerful design by using only 2 blocks with 2 periods each. The modest additional complexity of the proposed multi-period crossover design, compared to a parallel-groups design, is justified by the marked improvement in efficiency. The gains in efficiency afforded by the multi-period crossover design allow a substantial reduction in sample size without sacrificing statistical power.

The trial will compare an active treatment vs. placebo. Each block will consist of two treatment periods with each period lasting 6 weeks. Treatment assignments (active drug versus placebo) will be randomized for each patient to the two periods within each block. The period length of 6 weeks was chosen based on several considerations: (i) Most efficacious analgesic drugs demonstrate separation from placebo by 6 weeks; (ii) The decision to move CNTX-6970 forward to Phase 3 will require a clinically meaningful separation from placebo by 6 weeks; (iii) In this Phase 2 study, implementing a treatment block longer than 6 weeks would make the overall design more challenging and burdensome by extending the duration of overall testing beyond 6 months; (iv).

In this study, the placebo will consist of inactive tablets identical to the active treatment tablets. Treatment assignments (active drug versus placebo) will be randomized for each patient to the two treatment periods within each block.


Knee Osteoarthritis, Osteoarthritis, CNTX-6970


For people ages 40-90

A subject will be eligible for study participation if they meet all of the following criteria:

  1. Individuals between 40 and 90 years of age (inclusive) at the time of the Screening Visit.
  2. Willing to use a mobile smart device during the study period. Individuals who do not have access to a mobile device will be provided with one for the duration of the study and trained in its use.
  3. Can understand the nature of the study and protocol requirements and is willing to comply with study drug administration requirements and discontinue prohibited concomitant medications.
  4. Radiography of both knees with a posterior-anterior, fixed-flexion view taken during the Screening visit. The Index knee must show evidence of chronic OA with a K-L Grading Scale of 1, 2, 3, or 4. Such evidence will be provided by a central reading of the radiography of both knees from an expert radiologist of the CCC of EPPIC-Net.
  5. Moderate to severe pain in the Index knee associated with OA and stable for a minimum of 6 months prior to Screening in the opinion of the investigator.
  6. Confirmation of OA of the index knee: American College of Rheumatology (ACR) diagnostic criteria.
  7. Subjects must have failed 2 or more prior therapies. Failure is deemed to be inadequate relief in the opinion of the investigator.
  8. Body mass index (BMI) of ≤ 40 kg/m2.
  9. Willing to refrain from illicit drug use during the study, and to have illicit drug testing at screening and at later time points.

A subject will be excluded from the study if they meet any of the following criteria:

  1. Any form of joint replacement surgery, open surgery, or arthroscopic surgery of the index knee/knee joint with 12 months of Screening.
  2. Any painful condition(s) of the index knee due to disease other than OA. For example, periarticular or referred pain involving the index knee, or from joint disease other than OA associated with the index knee.
  3. Other chronic pain anywhere in the lower extremities (e.g. hips, legs, feet) that is equal or greater in intensity or impairment than index knee pain or that requires the use of analgesic medications. This includes radicular low back pain with radiation to the knee.
  4. Documented history of neuropathic arthropathy in the knee.
  5. Significant instability (e.g., cruciate ligament tear or rupture or previous repair) within the past 5 years or current misalignment (>10 degrees varus or valgus) of the index knee.
  6. Plans to have surgery, invasive procedures, or intra-articular (IA) injections of the index knee or procedure or surgery otherwise contraindicated for study participation while in the study.
    1. Concomitant Medications for Pain - i. Continuous use of one of the following medications prescribed for pain: tramadol, gabapentin, duloxetine, pregabalin, milnacipran, or tricyclic antidepressants that is:
    2. chronic for at least 12 weeks; and
    3. at a stable dose for at least 4 weeks before Screening ii. Intermittent use of opioids that is:
    4. ongoing for at least 4 weeks before Screening;
    5. at a frequency no more than 4 days/week; and
    6. not be taken within 24 hours of a study visit

    iii. As needed use of acetaminophen iv. Continuous use of medical marijuana (or equivalent) that is chronic for at least 12 weeks and at a stable dose for 4 weeks v. Topical creams (includes CBD topicals)

    1. Continuous use allowed if chronic and stable for at least 12 weeks
    2. Intermittent use allowed if at a frequency of no more than 4 days/week
    3. Concomitant Medications for Non-Pain Indications That May Impact Pain - i. Continuous use of medication for non-pain indications that are known to potentially impact pain, e.g. duloxetine for depression, that is at a stable dose for at least 12 weeks prior to Screening.

    ii. Low-dose aspirin for the purposes of heart disease prophylaxis

  7. Corticosteroid injection in the index knee within 30 days of Screening or during study participation (unless the injectable is a long-acting agent such as triamcinolone acetonide extended-release injectable suspension (Zilretta) in which case the injection cannot be within 90 days of screening).
  8. Received IA viscosupplementation (e.g., Synvisc®, Hyalgan®) within 90 days of Screening.
  9. Use of an investigational medication within 30 days of Screening, or 5 pharmacokinetic or pharmacodynamic half-lives (whichever is longer) or scheduled to receive such an agent while participating in the current study.
  10. Current therapy with any immunosuppressive therapy, including corticosteroids (>5 mg/day of prednisone).


  • University of California San Diego
    La Jolla California 92037 United States
  • University of California- Davis
    Sacramento California 95817 United States


in progress, not accepting new patients
Start Date
Completion Date
Maurizio Fava, MD
Phase 2 Osteoarthritis Research Study
Study Type
About 77 people participating
Last Updated