Aridis Pharmaceuticals (NASDAQ:ARDS) monoclonal antibody therapy AR-301 failed the main goal in a phase 3 trial to treat Ventilator Associated Pneumonia (VAP) caused by Gram-positive bacteria Staphylococcus aureus (S. aureus).

The study, dubbed AR-301-002, evaluated the superiority of adjunctive use of AR-301 with standard of care (SOC) antibiotics versus SOC antibiotics alone.

The study enrolled 174 mechanically ventilated intensive care unit (ICU) patients who were likely to have pneumonia caused by S. aureus, with 120 patients ultimately meeting the criteria. According to Aridis the target sample size was 240 which was impacted by the pandemic and conflict in Eastern Europe.

The company said statistical significance was not reached for the main goal of clinical cure rate on Day 21 compared to antibiotics alone. Clinical cure at Day 21 was 68.9% (42/61 patients) for AR-301 + SOC, compared to 57.6% (34/59) for SOC alone.

In older adults of 65+ years, the absolute efficacy (improvement in clinical cure rate) on Day 21 was increased to 34%, and to 38% on Day 28. The increase in absolute efficacy was driven mainly by the lower efficacy of SOC antibiotics in older adults 65+ years old compared to adults less than 65 years old (30% vs. 75%, respectively), the company added.

In patients with methicillin resistant S. aureus (MRSA), the absolute efficacy was 28% higher than SOC alone, according to Aridis.

The company noted that AR-301 was linked with reduction trends in key secondary outcomes, such as measures of duration of hospitalization (median 19 vs. 28 days), time in ICU (median 13 vs. 20 days), and mechanical ventilation days (median 6 vs. 8 days).

The all-cause mortality rates in all patients were — AR-301: 23.6% (21/89) versus SOC: 18.8% (16/85). These deaths were mainly linked with patients’ underlying conditions, as per the company.

Aridis said AR-301 intravenous (IV) infusion was well tolerated.

“Despite the limitations of sample size and lack of statistical significance in the primary endpoint, we are pleased to see the clinical benefit trends across the study population,” said Aridis’ Chief Medical Officer Hasan Jafri.

AR-301-002 is the first of two planned phase 3 studies of AR-301. Aridis plans to start the second phase 3 trial after discussing the current study results with regulatory authorities, including in the U.S. and EU.

ARDS -28.02% to $0.89 premarket Jan. 26