Armata is committed to developing novel phage therapies that specifically address areas of high need. We have an acute bacterial infection clinical development plan focused on complicated bacteremia due to Staphylococcus aureus, a difficult-to-treat and often life-threatening human infection that can result in high morbidity and mortality and for which bacterial resistance to antibiotics is growing.
AP-SA02
AP-SA02 is a fixed multi-phage product candidate that targets Staphylococcus aureus, and offers robust therapeutic attributes, including:
- Potent antimicrobial activity against approximately 95% of S. aureus clinical isolates tested, including methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains;
- Unique mechanism of action offers independent or synergistic benefit with standard of care antibiotics;
- Component phages are stable and retain infectivity after exposure to relevant biological fluids;
- Penetrates pre-existing S. aureus biofilms.
Clinical trial material of AP-SA02 is manufactured under cGMP at our production facility in Los Angeles, California to support the required regulatory filing(s) for clinical studies in the U.S. and ex-U.S.
Clinical Development of AP-SA02: diSArm Study
The “diSArm” study (NCT05184764) is a Phase 1b/2a, multienter, randomized, double‐blind, placebo‐controlled, multiple ascending dose escalation study of the safety, tolerability, and efficacy of intravenous AP‐SA02 in addition to best available antibiotic therapy (BAT) compared to BAT alone (placebo) for the treatment of adults with complicated bacteremia due to Staphylococcus aureus. The study was conducted at sites in the United States and also at sites abroad in Australia.
The Phase 1b/2a study was partially funded by a $26.2 million Department of Defense (DoD) award, received through the Medical Technology Enterprise Consortium (MTEC) and managed by the Naval Medical Research Command (NMRC) – Naval Advanced Medical Development (NAMD) with funding from the Defense Health Agency and Joint Warfighter Medical Research Program.
In May 2025, we announced positive topline results from the diSArm study. In October 2025, Dr. Loren G. Miller, M.D., M.P.H., Professor of Medicine, David Geffen School of Medicine at UCLA, Chief, Division of Infectious Diseases at Harbor-UCLA Medical Center and the Lundquist Institute, highlighted positive results from the diSArm study in a late-breaking oral presentation at IDWeek 2025.
Safety and efficacy were assessed in the intent-to-treat (ITT) population, which included all subjects (n=50) who received at least one dose of AP-SA02 or placebo. The Phase 2a study enrolled and dosed 42 patients, with 29 randomized to AP-SA02 in addition to BAT and 13 to placebo (BAT alone). MRSA was the causative pathogen in ~38% of both the AP-SA02 and placebo groups.
AP-SA02, administered IV every six hours for five days, was well-tolerated, with no serious adverse events related to the study drug. Two subjects had adverse events that were possibly related to the study drug: one with transient liver enzyme elevation and one with hypersensitivity that resolved with discontinuation of vancomycin.
The primary clinical efficacy endpoint for the Phase 2a portion of the diSArm study was clinical outcome (responder rate) in subjects with complicated bacteremia, measured at (i) Test of Cure (“TOC”) for AP-SA02, defined as one week following the end of IV treatment with AP-SA02 (day 12), (ii) TOC for BAT, defined as one week following the end of IV BAT, and (iii) end of study (“EOS”), defined as four weeks following the end of IV BAT. Clinical outcome was evaluated by both the blinded site investigators and a blinded Clinical Efficacy Adjudication Committee (CEAC) in the ITT population.
A statistically significant increase in clinical response rate was observed at TOC for AP-SA02 (day 12) in AP-SA02 treated subjects (88%; 21/24) versus placebo (58%; 7/12) (p = 0.047) as assessed by blinded site investigators, and 83% (20/24) in the AP-SA02 group versus 58% (7/12) in the placebo group as assessed by the blinded CEAC. At TOC for BAT and at EOS, 100% of the AP-SA02 treated subjects had clinically responded (p = 0.017) versus 25% of placebo subjects considered non-responsive due to either relapse or treatment failure, consistent with the non-responder rate reported in the literature for recent phase 3 trials. Of note, the clinical response with AP-SA02 occurred regardless of whether subjects were infected with MSSA or MRSA. All subjects infected with MRSA and treated with AP-SA02 and BAT cleared their infection by TOC for BAT with no evidence of relapse through EOS, as compared to the relapse rate of BAT alone as noted above. Supporting the investigator assessment, clinical outcome was assessed by the CEAC, who agreed that subjects who received placebo had a 22% and 25% non-responder rate at TOC with BAT and at EOS, respectively, while 100% of the subjects who received AP-SA02 clinically responded (p = 0.025: TOC BAT; p = 0.020: EOS).
Additionally, patients treated with AP-SA02 showed trends toward rapid normalization of key predictors of mortality and complications in SAB including C-reactive protein and interleukin-10, shorter time to negative blood culture, quicker time to resolution of signs and symptoms at the infection site, shorter intensive care unit and hospital utilization.
Defined and reproducible laboratory derived stable genomic variants present in AP-SA02 drug product may provide an immediate advantage, enabling rapid, strain-specific response to each patient’s S. aureus isolate. These characterized variants can expand from as little as 2% to dominance when infecting certain patient isolates in vitro, highlighting that these variants are favored for their enhanced ability to infect those clinical strains and the importance of integrating this diversity into Armata’s phage cocktail from the outset. This inherent flexibility may be central to achieving optimal therapeutic efficacy in the clinic.
Conclusions:
- AP-SA02, combined with BAT, had a higher and earlier cure rate compared to placebo in patients with complicated SAB at day 12 as assessed by both blinded site investigators and independent adjudicators.
- No patients who received AP-SA02 demonstrated non-response or relapse at one week post-BAT or at EOS, as assessed by both blinded site investigators and the independent adjudication committee, compared with approximately 25% non-response or relapse in the placebo group.
- AP-SA02 appears safe with clinical efficacy against both MRSA and MSSA and trends toward earlier resolution and shorter hospitalization, with no evidence of relapse four weeks post-therapy.
- We previously demonstrated the persistence of AP-SA02 in the IV space on multiple days one hour post IV push. These trial results support AP-SA02 homing to different sites of infection, presumably penetrating biofilms, and infecting and lysing the target S. aureus bacteria, independent of both antibiotic resistance patterns and site of infection.
- Defined phage variants in AP-SA02 drug product ensure an intrinsic adaptive mechanism — a flexibility that may be key to achieving effective phage therapy from patient to patient.
The results from our Phase 1b/2a diSArm study are an important step forward in our effort to confirm the potent antimicrobial activity of phage therapy and the completion of the study represents a significant milestone in the development of AP-SA02, moving Armata one step closer to introducing an effective new treatment option to patients suffering from complicated S. aureus bacteremia. This is the first clear evidence in a randomized controlled trial of the efficacy of phage against a serious systemic pathogen that is responsible for significant morbidity and mortality in the US.
In January 2026, Armata announced the conclusion of an End-of-Phase 2 (EOP2) written response from the U.S. FDA and plans to advance AP-SA02 into a Phase 3 clinical study in complicated S. aureus bacteremia. FDA’s Center for Biologics Evaluation and Research (CBER) division confirmed that the safety and efficacy data from Armata’s Phase 2a diSArm study support advancement to Phase 3. The FDA provided critical guidance on key elements of the Phase 3 study design, which will assess the superiority of AP-SA02 over the current standard of care for the treatment of complicated S. aureus bacteremia. The Phase 3 study is anticipated to initiate in the second half of 2026.
In February 2026, under Section 505E of the Federal Food, Drug, and Cosmetic Act, the FDA designated AP-SA02 for intravenous use as a Qualified Infectious Disease Product Designation (QIDP) for adjunct treatment of complicated bacteremia caused by methicillin-sensitive or methicillin-resistant S. aureus. To achieve QIDP designation, a drug candidate must be intended to treat serious or life-threatening infections, particularly those caused by bacteria and fungi that are resistant to treatment, or that treat qualifying resistant pathogens identified by the FDA. The QIDP designation makes AP-SA02 eligible to benefit from certain incentives for the development of new antibacterials provided under the Generating Antibiotic Incentives Now (GAIN) Act, including an additional five-year extension of Hatch-Waxman market exclusivity. Further, the QIDP designation makes AP-SA02 eligible for Fast Track status, which provides an opportunity for more frequent meetings and communication with the FDA, priority and rolling review, leading to potential accelerated approval of its Biologics License Application. The Company plans to submit to the FDA a request for Fast Track Designation for AP-SA02.
Target Market and Medical Need
Bacteremia is a bacterial infection of the bloodstream. A common diagnosis, the Centers for Disease Control and Prevention (CDC) estimates that up to 1.7 million people in the U.S. develop bacteremia each year. S. aureus is the most commonly identified pathogen in both hospital- and community-acquired blood stream infections. Annually in the U.S. there are more than 150,000 hospitalizations for S. aureus bacteremia (SAB). Despite conventional antibiotics, mortality in SAB results in death of up to 40% of all cases and 57% of patients over the age of 85. Patients with comorbidities such as alcoholism, malignancy, diabetes, end-stage renal disease requiring hemodialysis, and immunosuppression are at even higher risk for death when SAB develops. Age-adjusted mortality assessments show that SAB mortality is higher than that of AIDS, tuberculosis, or viral hepatitis, and comparable to mortality rates for breast or prostate cancer. Outcomes are even poorer for SAB due to methicillin-resistant S. aureus (MRSA), classified as a serious threat to global health by the CDC and a high priority threat by the World Health Organization, with higher rates of complications and increased mortality as compared to methicillin-susceptible S. aureus (MSSA). Average hospital costs to patients with nosocomial SAB ranges between $40,000 (MSSA) and $114,000 (MRSA). Treatment failures are common in SAB, with highest rates due to MRSA. These failures can be attributed in part to poor penetration of some tissues by antibiotics, slow onset of bactericidal effects, emerging resistance patterns, and biofilm formation. While biofilms can render traditional antibiotics ineffective, phages may have the ability to penetrate the biofilm allowing rapid and efficient infection of the host and amplification at the site of infection. Until the recent FDA approval of Zevtera (intravenously administered cephalosporin antibiotic), daptomycin (approved in 2005; based on clinical cure rates of <50%) and vancomycin were the only two antibiotics with label indications in the U.S. for the treatment of SAB, and the emergence of drug-resistant S. aureus isolates, including to these two standard of care drugs, represents a major threat in terms of increasing morbidity, mortality and health care utilization.
Additional Clinical Indications for AP-SA02
Improved patient outcomes are needed for other Staphylococcal infections, in settings such as prosthetic joint infections and wound infections, for which antimicrobial resistance is a growing concern. We believe AP-SA02 could also have a meaningful impact in these indications, particularly infections caused by methicillin-resistant S. aureus (MRSA). In August, 2022, the U.S. FDA cleared Armata’s Investigational New Drug (IND) application for AP-SA02 in a second indication, prosthetic joint infection (PJI).