Our lead drug, otenaproxesul, is being developed as a safer non-opioid analgesic for post-operative pain

Otenaproxesul is a novel nonsteroidal anti-inflammatory drug (“NSAID”) that releases hydrogen sulfide. Antibe is leveraging the drug’s remarkable potency, gastrointestinal (“GI”) protection and overall safety profile for use in acute pain indications. Initially targeting the $13 billion1 post-operative pain segment, we plan to expand to indications such as migraine, dysmenorrhea, gout and traumatic injury—all large markets with few safe and effective therapies.


Addressing a Clear Unmet Medical Need...

NSAIDs are increasingly employed in post-operative pain management to replace opioids, and as a component of multimodal analgesia, a growing practice whereby multiple drugs are administered to achieve optimal pain reduction. While NSAIDs are effective, they can cause a range of GI-related adverse effects. Even in short-term use, they triple the risk of serious GI outcomes.2 Celecoxib (branded as Celebrex) offers some improvement in GI safety, but its use is associated with cardiovascular toxicity. Notably, opioids also can cause adverse GI effects, including nausea, vomiting and severe constipation—leading to patient discomfort and costs of extended hospitalization.3

Preclinical Studies

Otenaproxesul demonstrates significant GI safety

The drug remained GI-safe when administered to animals with compromised mucosal defense or pre-existing ulcers—situations in which today’s NSAIDs (including celecoxib) can cause ulcers and bleeding in humans. Otenaproxesul also remained safe when co-administered with aspirin. In addition, otenaproxesul did not elevate blood pressure when administered to rats with hypertension, in contrast to naproxen’s hypertensive effect.

Human Trials

Profound Phase IIB gastrointestinal safety results

In 2018, Antibe completed a Phase IIB GI safety trial of otenaproxesul in 244 healthy volunteers. It was designed to demonstrate superiority of otenaproxesul compared to naproxen, one of the most prescribed NSAIDs. One group was treated for 14 days with otenaproxesul (250 mg, once daily), while the other group was treated for the same period with the standard prescription dose of naproxen (550 mg, twice daily, totaling 1,100 mg per day). The study’s primary endpoint was the incidence of gastric or duodenal ulcers of at least 3 mm diameter with unequivocal depth, considered the ‘gold standard’ in assessing the GI safety of NSAIDs.

Otenaproxesul successfully met the primary endpoint in the study. Subjects on otenaproxesul exhibited an ulceration rate of 2.5% (3/118) versus an ulceration rate of 42.1% (53/126) for subjects on naproxen at the end of the treatment period, with a very high degree of statistical significance (p<0.0001). 

Robust Phase IIB efficacy results

In June 2020, Antibe reported positive top-line results from its Phase IIB dose ranging, efficacy study designed to validate the efficacy of otenaproxesul in reducing chronic pain. The study involved 384 participants across 39 sites.

Subjects were randomized to placebo or one of three doses of otenaproxesul administered once daily: 150 mg, 200 mg or 250 mg. The primary endpoint was the change in the WOMAC pain subscale scores (the ‘gold standard’ in chronic pain assessment) over a 14-day treatment period. The results showed a high degree of statistical significance for the 200 mg and 250 mg doses, thereby demonstrating efficacy in pain reduction. The lowest dose, although not powered for statistical significance, showed a positive trend toward efficacy.

Further validating the WOMAC pain measures, otenaproxesul delivered profound COX inhibition, exceeding 90% for all doses, at very high degrees of statistical significance (p<0.0002).

The chart above depicts the pain efficacy of otenaproxesul in a 14-day treatment regimen for three doses. The vertical bars depict the improvement in WOMAC pain subscale scores for each of the doses after two weeks of administration. The horizontal dotted line indicates the average efficacy of NSAIDs after 12 (or more) weeks, as set out in Comparative Pain Reduction of Oral Non-steroidal Anti-inflammatory Drugs and Opioids for Knee Osteoarthritis: Systematic Analytic Review; Osteoarthritis and Cartilage, S.R. Smith et al., 2016.5

These results support the success of an earlier Phase IIA open-label, effectiveness study. Its primary endpoint was the clinical assessment of pain over the ten-day course of treatment at 250 mg once-daily (n = 12), delivering a significant WOMAC pain score reduction on day 10, at a very high level of statistical significance in comparison to baseline pain (p<0.001).

Development Plan

Leveraging otenaproxesul’s extensive human safety and efficacy data, Antibe  launched its clinical program for post-operative pain in early 2022. To identify the drug’s go-forward treatment regimens, Antibe is conducting a series of brief pharmacokinetic and pharmacodynamic (“PK/PD”) clinical studies, including the investigation of loading doses to achieve rapid analgesic onset.

In late 2022, with optimal treatment regimens identified and commercial data in hand (see sidebar), Antibe expects to launch otenaproxesul’s Phase II program. Involving a single efficacy trial with a treatment period of up to 10 days, top-line data is expected within six months. This trial will employ a surgical bunionectomy model, recognized as one of most reliable surgical procedures for evaluating analgesic efficacy.

Upon success of the Phase II program, Antibe will request an End of Phase 2 meeting with the US FDA to discuss the Phase III program. Given the short treatment durations in acute pain trials, we

Commercial Plan

The post-operative pain segment is an ideal springboard to the much broader acute pain market. With the lack of recent innovation in oral analgesics and the urgent need for non-addictive alternatives, Antibe expects otenaproxesul to be especially attractive to potential partners. To further refine our strategy, we have commissioned a comprehensive market opportunity and reimbursement study, including revenue projections for the large markets, with results expected in mid-2022.

Further information on our commercial plan for otenaproxesul is available in our Corporate Presentation.

anticipate that the Phase III program can be completed within 12 months of initiation. This includes two concurrent, pivotal efficacy trials to assess post-operative pain relief for the following surgical procedures: (i) the hard-tissue model of bunionectomy, replicating the Phase II trial with a larger sample size; and (ii) abdominoplasty, a widely accepted soft-tissue surgical model. Following Phase III, Antibe intends to apply for marketing approval for a broad acute pain indication.

Antibe is also investigating alternative dosing regimens as a potential path forward for chronic indications.

1. Transparency Market Research (2019), 2021 projection.
2. Fine M, Am J ManagCare (2013);19(16 suppl):S267-S272.
3. Whitman CJ et al., J Opioid Manag (Sep-Oct 2015)11(5):383-91.
4. Post hoc analysis. Results do not necessarily predict future efficacy results.
5. Smith SR et al., Osteoarthritis and Cartilage (2016);24: 962-972.


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