Synthetic Biologics Reports 2020 First Quarter Operational Highlights and Financial Results -- Company Updates Guidance and Clinical Development Timeline in Response to the COVID-19 Global Pandemic -- -- Conference Call

Synthetic Biologics Reports 2020 First

Quarter Operational Highlights and Financial Results

-- Company Updates Guidance and Clinical

Development Timeline

in Response to the COVID-19 Global

-- Conference Call Today at 4:30 p.m.

MD, May 5, 2020 - Synthetic Biologics, Inc. (NYSE American: SYN), a diversified

clinical-stage company leveraging the microbiome to develop therapeutics designed to prevent and treat gastrointestinal (GI) diseases

in areas of high unmet need, today provided a clinical programs update and reported financial results

for the quarter ended March 31, 2020.

"During the first quarter of 2020,

we remained sharply focused on executing our strategy to advance our portfolio of GI and microbiome-focused clinical development

programs while responding to the unprecedented global health and economic crisis sparked by the COVID-19 pandemic," said

Steven A. Shallcross, Chief Executive and Financial Officer of Synthetic Biologics. "Recommendations by local governments,

hospitals and healthcare organizations to concentrate resources towards COVID-19 care are having a material impact on ongoing and

planned clinical trials. This includes our ongoing Phase 2b investigator-sponsored clinical trial of SYN-010, intended to treat

irritable bowel syndrome with constipation (IBS-C), being conducted out of Cedars-Sinai Medical Center (CSMC), as well as our planned

Phase 1b/2a clinical trial of SYN-004 (ribaxamase) in allogeneic hematopoietic cell transplant (HCT) recipients, which will be

conducted by the Washington University School of Medicine in St. Louis (Washington University).Although we have experienced additional

delays in enrollment and site visits for our planned and ongoing clinical trials, we believe we have implemented an operational

framework which will allow us to navigate this crisis and ultimately deliver on the tangible results and goals we have established

Mr. Shallcross continued, "During

the first quarter, we continued to make significant progress towards the completion of Investigational New Drug (IND)-enabling

toxicology studies and assay development that are expected to support the filing of an IND for our SYN-020 intestinal alkaline

phosphatase (IAP) program during the second quarter of 2020." Mr. Shallcross concluded, "In response to the efforts

undertaken by our clinical development partners to conserve resources for combatting COVID-19, we have been able to reduce our

burn rate and further extend our cash runway through at least the first quarter of 2021. We are monitoring the crisis caused by

the spread of the COVID-19 closely and remain dedicated to protecting the health and safety of our employees, our clinical development

partners and our patients."

Clinical Development and Operational

Quarter Ended March 31, 2020 Financial

General and administrative expenses increased

by 21% to $1.4 million for the three months ended March 31, 2020, from $1.1 million for the three months ended March 31, 2019.

This increase is primarily due to increased insurance costs, registration fees, and legal costs. The charge related to stock-based

compensation expense was $65,000 for the three months ended March 31, 2020, compared to $65,000 the three months ended March 31,

Research and development expenses decreased

by 32% to $1.6 million for the three months ended March 31, 2020, from $2.4 million for the three months ended March 31, 2019.

This decrease is primarily the result of lower indirect program costs for the three months ended March 31, 2020, including salary

and related expense reductions resulting from the 2019 headcount reductions and a decrease in manufacturing costs for SYN-020.

The research and development costs incurred during the quarter were primarily related to the investigator-sponsored Phase 2b clinical

study of SYN-010. We anticipate research and development expense to decrease as a result of the response to the global COVID-19

pandemic by our clinical development partners which has led to the postponement of the Phase 1b/2a clinical trial of SYN-004 (ribaxamase)

in allogeneic HCT recipients and a temporary halt in new enrollment in the Phase 2b investigator sponsored clinical trial of SYN-010.

The charge related to stock-based compensation expense was $18,000 for the three months ended March 31, 2020, compared to no charge

related to stock-based compensation expense for the three months ended March 31, 2019 resulting from the 2018 restructuring.

Other income was $38,000 for the three

months ended March 31, 2020, compared to other income of $44,000 for the three months ended March 31, 2019. Other income for the

three months ended March 31, 2020 and 2019 is primarily comprised of interest income.

Cash and cash equivalents as of March 31,

2020 totaled $10.1 million, a decrease of $5.0 million from December 31, 2019.

Synthetic Biologics will hold a conference call today, Tuesday,

May 5, 2020, at 4:30 p.m. (EST).

The dial-in information for the call is as follows, U.S. toll free: 1-888-347-5280 or International: +1 412-902-4280. Participants

are asked to dial in 15 minutes before the start of the call to register. The call will also be webcast over the Internet at https://www.webcaster4.com/Webcast/Page/1096/34417.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/34417,

for 90 days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE American:

SYN) is a clinical-stage company leveraging the microbiome to develop therapeutics designed to prevent and treat gastrointestinal

(GI) diseases in areas of high unmet need. The Company's lead clinical candidates are: (1) SYN-004 (ribaxamase) which is designed

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

damage, C. 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, and (2) SYN-010, which

is intended to reduce the impact of methane-producing organisms in the gut microbiome to treat an underlying cause of irritable

bowel syndrome with constipation (IBS-C). The Company is also advancing SYN-020, an oral formulation of the enzyme intestinal

alkaline phosphatase (IAP) to treat both local GI and systemic diseases. For more information, please visit Synthetic Biologics'

website at www.syntheticbiologics.com.

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 commencement of the planned Phase 1b/2a investigator-sponsored clinical study in allogeneic HCT

patients in the first quarter of 2021, anticipated data readout for the investigator-sponsored Phase 2b clinical study for SYN-010

during the third quarter of 2020, anticipated IND filing for SYN-020 in the second quarter of 2020, SYN-004's degrading certain

commonly used intravenous (IV) beta-lactam antibiotics within the gastrointestinal tract to prevent microbiome damage, C. difficile

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

in allogeneic hematopoietic cell transplant (HCT) recipients, and SYN-010 reducing the impact of methane-producing organisms in

the gut microbiome to treat an underlying cause of irritable bowel syndrome with constipation. 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, a failure to receive the necessary regulatory

approvals for commercialization of Synthetic Biologics' therapeutics, a failure of Synthetic Biologics' clinical trials,

and those conducted by investigators, for SYN-004 and SYN-010 to be commenced or completed on time or to achieve desired results

and benefits, especially in light of COVID-19, a failure of Synthetic Biologics' clinical trials to continue enrollment as

expected or receive anticipated funding, a failure of Synthetic Biologics to successfully develop, market or sell its products,

Synthetic Biologics' inability to maintain its material licensing agreements, or a failure by Synthetic Biologics or its

strategic partners to successfully commercialize products and other factors described in Synthetic Biologics' Annual Report

on Form 10-K for the year ended December 31, 2019 and its other filings with the SEC, including subsequent periodic reports on

Forms 10-Q and 8-K. The information in this release is provided only as of the date of this release, and Synthetic 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:

Synthetic Biologics, Inc. (Corporate and

Vincent I. Perrone, Director Corporate Communication, (240)

660-2000, info@syntheticbiologics.com

Gregory Kelley, Senior Vice President, (404) 836-2302, gregory.kelley@ogilvy.com

- Financial Tables Follow -