Synthetic Biologics Reports 2019 Year End Operational Highlights and Financial Results -- Received FDA Guidance Following Type-C Meeting to Conduct a Phase 1b/2a Clinical Trial of SYN-004 (ribaxamase) in Allogeneic HCT R

Synthetic Biologics Reports 2019 Year

End Operational Highlights and Financial Results

-- Received FDA Guidance Following

Type-C Meeting to Conduct a Phase 1b/2a Clinical Trial of

SYN-004 (ribaxamase) in Allogeneic

HCT Recipients; Enrollment Expected in Q2 2020 --

-- Enrollment is Ongoing in Phase

2b Investigator-Sponsored Clinical Study of SYN-010

for the Treatment of IBS-C

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

MD, February 20, 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 year ended December 31, 2019.

"2019 was a highly eventful period

marked by significant progress as we continued to execute our strategy to advance and demonstrate the significant value of our

portfolio of GI and microbiome-focused clinical programs," stated Steven A. Shallcross, Chief Executive and Financial Officer.

"Following the announcement of our clinical trial collaboration with the Washington University School of Medicine in St.

Louis ("Washington University") to advance SYN-004 in allogeneic hematopoietic cell transplant (HCT) patients, we held

an extremely productive Type-C meeting with the U.S. Food and Drug Administration ("FDA") to finalize the clinical

program parameters of a Phase 1b/2a clinical trial expected to begin next quarter. Allogeneic HCT recipients who receive broad-spectrum

IV beta-lactam antibiotics at onset of fever following conditioning chemotherapy are at high risk for Clostridioides difficile

infection (CDI), colonization by vancomycin-resistant Enterococci (VRE) and acute graft-versus-host-disease (aGVHD). We

believe SYN-004's unique mechanism of action designed to degrade IV beta-lactam antibiotics and prevent dysbiosis of the

gut microbiome has the potential to significantly improve outcomes for patients who undergo allogeneic HCT, an area of significant

Mr. Shallcross continued, "Enrollment

in our investigator-sponsored Phase 2b clinical study for SYN-010 in breath-methane positive irritable bowel syndrome with constipation

(IBS-C) patients remains ongoing. We anticipate a data readout sometime during the first half of 2020 which we believe will further

fortify the established clinical data set for SYN-010 and support regulatory discussions to potentially simplify future registration

studies. Preclinical activities and toxicology studies are ongoing and remain on track to support a near-term Investigational New

Drug Application (IND) filing for our SYN-020 Intestinal Alkaline Phosphatase (IAP) program. We look forward to sharing important

updates and progress for this and all our GI and microbiome-focused clinical programs."

Clinical Development and Operational

Year Ended December 31, 2019 Financial

General and administrative expenses decreased

to $4.6 million for the year ended December 31, 2019, from $5.7 million for the year ended December 31, 2018. This decrease of

19% is due to decreased stock-based compensation expense related to forfeitures and decreased option grants, along with the reduction

of investor relations, consulting, registration, and legal costs. The charge relating to stock-based compensation expense was $0.3

million for the year ended December 31, 2019, compared to $1.0 million for the year ended December 31, 2018.

Research and development expenses decreased

to $11.1 million for the year ended December 31, 2019, from $11.8 million for the year ended December 31, 2018. This decrease of

6% is primarily the result of lower SYN-004 (ribaxamase) indirect program costs for the year ended December 31, 2019, including

salary and related expense reductions resulting from the 2018 restructuring, and the fact that no clinical trial activity for SYN-004

(ribaxamase) was ongoing during the year ended December 31, 2019, offset by an increase in manufacturing and pre IND-enabling toxicology

study costs for SYN-020. Research and development expenses also include a charge relating to non-cash stock-based compensation

expense of $75,000 for the year ended December 31, 2019, compared to $1.1 million for the year ended December 31, 2018.

Total other income was $283,000 for the

year ended December 31, 2019, compared to other income of $4.2 million for the year ended December 31, 2018. Total other income

for the year ended December 31, 2019 is primarily comprised of interest income while total other income for the year ended December

31, 2018 is comprised of non-cash income of $4.1 million from the change in fair value of warrants. The decrease in the fair value

of warrants was due to the decrease in our stock price from December 31, 2017 to December 31, 2018.

Cash and cash equivalents on December 31,

2019 were $15.0 million, a decrease of $13.9 million from December 31, 2018.

Synthetic Biologics will hold a conference

call today, Thursday, February 20, 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/1096/32979.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/32979,

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 anticipated initiation of a Phase 1b/2a investigator-sponsored clinical study in allogeneic HCT

patients in the second quarter of 2020, the potential of SYN-004's unique mechanism of action designed to degrade IV beta-lactam

antibiotics and prevent dysbiosis of the gut microbiome to significantly improve outcomes for patients who undergo allogeneic

HCT, an area of significant unmet need, anticipated data readout for the investigator-sponsored Phase 2b clinical study for SYN-010

during the first half of 2020, the data readout further fortifying the established clinical data set for SYN-010 and supporting

regulatory discussions to potentially simplify future registration studies, anticipated IND filing for SYN-020 in the first half

of 2020. 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, 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' most

recent Form 10-K 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

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 -