Theriva Biologics Announces Presentation of Safety and Pharmacokinetic Data from Cohort 1 of the Phase 1b/2a Clinical Trial of SYN-004 (ribaxamase) in Allogeneic Hematopoietic Cell Transplant Recipients - Data presented

Theriva Biologics Announces Presentation of

Safety and Pharmacokinetic Data from Cohort 1 of the Phase

1b/2a Clinical Trial of SYN-004 (ribaxamase) in Allogeneic Hematopoietic Cell

Transplant Recipients

- Data presented at the 2023 Tandem Meetings:

Transplantation & Cellular Therapy Meetings of ASTCT and CIBMTR -

-Analysis of patients receiving meropenem suggest

that SYN-004 is well-tolerated with HCT and was not

observed in blood samples from the majority of the evaluable patients -

MD, February 16, 2023 - Theriva Biologics (NYSE American: TOVX), ("Theriva" or the "Company"),

a diversified clinical-stage company developing therapeutics designed to treat cancer and related diseases in areas of high unmet need,

today announced the presentation of blinded safety and pharmacokinetic (PK) data from the ongoing Phase

1b/2a randomized, double-blinded, placebo-controlled clinical trial of SYN-004 (ribaxamase) in allogeneic hematopoietic cell transplant

(HCT) recipients for the prevention of acute graft-versus-host-disease (aGVHD). These data will be featured in a poster presentation at

the 2023 Tandem Meetings: Transplantation & Cellular Therapy Meetings of ASTCT and CIBMTR, being held in Orlando, Florida from February

"SYN-004 (ribaxamase) is intended to address

key limitations of broad-spectrum IV beta-lactam antibiotics and potentially improve treatment outcomes with this important and widely

used class of therapeutics. We are encouraged by the favorable safety/tolerability profile and growing evidence from our initial meropenem

(MER) cohort that supports the clinical advancement of SYN-004," said Steven A. Shallcross, Chief Executive Officer of Theriva Biologics.

"With our collaborators at Washington University we plan to continue to explore the therapeutic potential of SYN-004 and its ability

to reduce serious adverse events in patients with hematologic cancers undergoing allogeneic HCT. Dosing is now underway for Cohort 2,

which is designed to evaluate SYN-004 in combination with piperacillin/tazobactam and we look forward to providing further updates on

Cohort 1 of the study enrolled 19 patients who

received at least 1 dose of study drug (SYN-004 or Placebo randomized 2:1). Twelve of these patients completed two doses of IV MER to

be evaluable towards the study endpoints. While the study is on-going and remains blinded, key findings showcased in the poster presentation

(#LBA6) titled "Interim Analysis of SYN-004 Phase 1b/2a Trial in Hematopoietic Cell Transplant (HCT) Recipients" include:

Details on the poster can be found below.

About the Phase 1b/2a Clinical Trial

The ongoing randomized, double-blinded, placebo-controlled Phase 1b/2a

clinical trial is being conducted at Washington University School of Medicine in St. Louis. The trial is designed to evaluate the safety,

tolerability, and potential absorption of oral SYN-004 (150 mg q.i.d. for a maximum of 28 days) into the systemic circulation of allogeneic

HCT recipients who receive an IV antibiotic to treat fever. To mitigate risk, Cohort 1 of the study administered meropenem as the study-assigned

antibiotic. Meropenem is a carbapenem antibiotic that is not metabolized by SYN-004. Patients in Cohorts 2 and 3 will be administered

piperacillin/tazobactam and cefepime respectively, each of which can be metabolized by SYN-004. The trial is also designed to evaluate

potential protective effects of SYN-004 on the gut microbiome as well as generate preliminary information on potential therapeutic benefits

and patient outcomes of SYN-004 in allogeneic HCT recipients. The trial is expected to enroll up to 36 participants with three sequential

cohorts, each evaluating a different study-assigned IV beta-lactam antibiotic. Safety and pharmacokinetic data for each cohort will be

reviewed by an independent Data and Safety Monitoring Committee that will make a recommendation on whether to proceed to the next IV beta-lactam

antibiotic. More information on the study is available here (NCT04692181).

About SYN-004 (ribaxamase)

SYN-004 (ribaxamase) is an oral prophylactic therapy designed to degrade

certain IV beta-lactam antibiotics within the GI tract and maintain the natural balance of the gut microbiome for the prevention of Clostridioides

difficile infection (CDI), overgrowth of pathogenic organisms, the emergence of antimicrobial resistance (AMR) and acute graft-versus-host-disease

(aGVHD) in allogeneic hematopoietic cell transplant (HCT) recipients. Allogeneic HCT recipients routinely receive long courses of IV beta-lactam

antibiotics to treat infection following conditioning therapy. Antibiotic-mediated damage of the gut microbiome in allogeneic HCT recipients

may lead to adverse outcomes including CDI, VRE colonization and potentially fatal bacteremia and aGVHD. A previously completed placebo-controlled

Phase 2b clinical trial of 412 patients demonstrated SYN-004 protected the gut microbiome from antibiotic-mediated dysbiosis. Patients

who received SYN-004 also demonstrated significantly better maintenance and recovery of the gut microbiome as well as lower incidences

of new colonization by opportunistic and potentially pathogenic microorganisms such as VRE.

About Theriva Biologics, Inc.

Theriva Biologics (NYSE American: TOVX), is a

diversified clinical-stage company developing therapeutics designed to treat cancer and related diseases in areas of high unmet need.

The Company's subsidiary Theriva Biologics, S.L. , has been developing a new oncolytic adenovirus platform designed for intravenous

(IV), intravitreal and antitumoral delivery to trigger tumor cell death, improve access of co-administered cancer therapies to the tumor,

and promote a robust and sustained anti-tumor response by the patient's immune system. The Company's lead clinical-stage

candidates are: (1) VCN-01, an oncolytic adenovirus designed to replicate selectively and aggressively within tumor cells, and to degrade

the tumor stroma barrier that serves as a significant physical and immunosuppressive barrier to cancer treatment; (2) SYN-004 (ribaxamase)

which is designed to degrade certain commonly used IV beta-lactam antibiotics within the gastrointestinal (GI) tract to prevent microbiome

damage, thereby limiting overgrowth of pathogenic organisms such as VRE (vancomycin resistant Enterococci) and reducing the incidence

and severity of acute graft-versus-host-disease (aGVHD) in allogeneic hematopoietic cell transplant (HCT) recipients); and (3) SYN-020,

a recombinant oral formulation of the enzyme intestinal alkaline phosphatase (IAP) produced under cGMP conditions and intended to treat

both local GI and systemic diseases. For more information, please visit Theriva Biologics' website at www.therivabio.com.

Forward-Looking Statement

This release contains forward-looking

statements within the meaning of the Private Securities Litigation Reform Act of 1995. In some cases forward-looking statements can

be identified by terminology such as "may," "should," "potential," "continue,"

"expects," "anticipates," "intends," "plans," "believes,"

"estimates," and similar expressions, and include statements regarding SYN-004 (ribaxamase) being intended to address

key limitations of broad-spectrum IV beta-lactam antibiotics and potentially improve treatment outcomes with this important and

widely used class of therapeutics, plans to continue to explore the therapeutic potential of SYN-004 and its ability to reduce

serious adverse events in patients with hematologic cancers undergoing allogeneic HCT, providing further updates on the

Company's progress, and the study enrolling up to 36 participants with three sequential cohorts, each evaluating a different

study-assigned IV beta-lactam antibiotic. These forward-looking statements are based on management's expectations and

assumptions as of the date of this press release and are subject to a number of risks and uncertainties, many of which are difficult

to predict that could cause actual results to differ materially from current expectations and assumptions from those set forth or

implied by any forward-looking statements. Important factors that could cause actual results to differ materially from current

expectations include, among others, the SYN-004's ability to address key limitations of broad-spectrum IV beta-lactam

antibiotics and potentially improve treatment outcomes with this important and widely used class of therapeutics, the

Company's and VCN's ability to reach clinical milestones when anticipated including enrolling the expected number of

patients in each trial, , the Company's and VCN's product candidates, including SYN-004, demonstrating safety and

effectiveness, as well as results that are consistent with prior results; the ability to complete clinical trials on time and

achieve the desired results and benefits, continuing clinical trial enrollment as expected; the ability to obtain regulatory

approval for commercialization of product candidates or to comply with ongoing regulatory requirements, regulatory limitations

relating to the Company's and VCN's ability to promote or commercialize their product candidates for the specific

indications, acceptance of product candidates in the marketplace and the successful development, marketing or sale of the

Company's and VCN's products, developments by competitors that render such products obsolete or non-competitive, the

Company's and VCN's ability to maintain license agreements, the continued maintenance and growth of the Company's

and VCN's patent estate, the ability to continue to remain well financed, and other factors described in the Company's

Annual Report on Form 10-K for the year ended December 31, 2021 and its other filings with the SEC, including subsequent periodic

reports on Forms 10-Q and current reports on Form 8-K. The information in this release is provided only as of the date of this

release, and Theriva Biologics undertakes no obligation to update any forward-looking statements contained in this release on

account of new information, future events, or otherwise, except as required by law.

For further information, please contact:

LifeSci Advisors, LLC