Synthetic Biologics Reports 2018 Year End Operational Highlights and Financial Results -- Enrollment is Ongoing in Phase 2b Investigator-Sponsored Clinical Study of SYN-010, for the Treatment of IBS-C; Topline Data Reado

Synthetic Biologics Reports 2018 Year

End Operational Highlights and Financial Results

-- Enrollment is Ongoing in Phase

2b Investigator-Sponsored Clinical Study of SYN-010,

for the Treatment of IBS-C; Topline

Data Readout Anticipated in 2H 2019 --

-- Conference Call Wednesday, February

27, 2019, at 4:30 p.m. (EST) --

Rockville, MD, February 27, 2019 -

Synthetic Biologics, Inc. (NYSE American: SYN), a clinical-stage

company developing therapeutics that preserve the microbiome to protect and restore the health of patients, today provided a clinical

programs update and reported financial results for the year ended December 31, 2018.

"During the fourth quarter, we remained

sharply focused on executing our strategy to advance and demonstrate the significant value of our portfolio of GI and microbiome-focused

clinical assets," stated Steven A. Shallcross, Chief Executive and Financial Officer. "We are pleased to report that

patient enrollment is continuing for our investigator-sponsored Phase 2b clinical trial of SYN-010, our modified-release formulation

of lovastatin lactone designed to treat an underlying cause of irritable bowel syndrome with constipation. We believe data derived

from this study will solidify our existing clinical outcomes data, including dose-response, and potentially simplify future registration

studies. We anticipate a topline data readout from this study in the second half of 2019."

Mr. Shallcross continued, "During

the fourth quarter, we also announced the results of our End-of-Phase 2 meeting with the U.S. Food & Drug Administration (FDA)

during which key elements of a Phase 3 clinical program were confirmed to support a marketing application for SYN-004 for the prevention

of Clostridium difficile infection (CDI). In parallel, we continue to evaluate strategies to pursue a secondary clinical

indication for SYN-004 in a specialized patient population which may allow for a more narrow and less costly clinical development

pathway. One such indication is the prevention of acute graft-versus-host-disease (aGVHD) in allogeneic hematopoietic cell transplant

(HCT) recipients, where protection of the gut microbiome from antibiotic damage may provide a distinct benefit to patient outcomes.

Discussions with key opinion leaders who are experts in allogeneic HCT are ongoing, and we look forward to sharing updates and

progress for this potential indication."

"With the steps we have taken at

the end of the fourth quarter to fortify our long-term financial footing, we have created a strong foundation upon which to execute

our strategy to advance and showcase the value of our late stage clinical assets. Our entire organization is excited and committed

to achieving the important clinical development milestones we have established for 2019," concluded Mr. Shallcross.

Clinical Development and Operational

Year Ended December 31, 2018 Financial

General and administrative expenses decreased

to $5.7 million for the year ended December 31, 2018, compared to $7.5 million for the year ended December 31, 2017. This decrease

of 24% is due to the decreased stock-based compensation expense related to forfeitures and share price, along with the reduction

of salary, travel and consulting expense, offset by higher registration, investor relations and legal costs. The charge relating

to stock-based compensation expense was $1.0 million for the year ended December 31, 2018, compared to $2.0 million for the year

ended December 31, 2017.

Research and development expenses decreased

to $11.8 million for the year ended December 31, 2018, from $18.8 million for the year ended December 31, 2017. This decrease of

37% is primarily the result of lower SYN-004 (ribaxamase) and SYN-010 program costs for 2018 since no clinical trials were ongoing

during the year. The research and development costs incurred during the quarter were primarily related to planning for future Phase

3 (SYN-004) and Phase 2b/3 (SYN-010) clinical programs as we sought to secure the financial resources necessary for the completion

of these clinical trials. We anticipate research and development expense to increase due to the ongoing Phase 2b investigator-sponsored

clinical trial for SYN-010 and development activities associated with the potential initiation of a Phase 1/2 investigator-sponsored

clinical trial for the prevention of aGVHD in HCT recipients for SYN-004. Research and development expenses also include a charge

relating to non-cash stock-based compensation expense of $1.1 million for the year ended December 31, 2018, compared to $1.4 million

for the year ended December 31, 2017.

Other income was $4.2 million for the year

ended December 31, 2018, compared to other income of $10.8 million for the year ended December 31, 2017. Other income for the year

ended December 31, 2018 is primarily due to 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.

In connection with the issuance and subsequent conversions of the Series B Convertible Preferred Stock

in 2018 and the issuance of the Series A Convertible Preferred Stock in 2017, the Company recognized non-cash deemed dividends

of $11.7 million and $6.9 million respectively, for the beneficial conversion feature resulting from the intrinsic value of the

Series B and Series A conversion options as of the issuance date.

Cash and cash equivalents on December

31, 2018 were $28.9 million, an increase of $11.8 million from December 31, 2017.

Synthetic Biologics will hold a conference

call today, Wednesday, February 27, 2019, 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/1096/29346.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/29346,

for 90 days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE American:

SYN) is a clinical-stage company developing therapeutics that preserve the microbiome to protect and restore the health of patients.

The Company's lead 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's

preclinical pursuits include SYN-020, an oral formulation of the enzyme intestinal alkaline phosphatase (IAP) to treat both local

GI and systemic diseases as well as monoclonal antibody therapies for the prevention and treatment of pertussis. 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 the belief that data derived from the investigator-sponsored Phase 2b clinical trial of SYN-010

will solidify Synthetic Biologics' existing clinical outcomes data, including dose-response, and potentially simplify future

registration studies, anticipated topline data readout from the investigator-sponsored Phase 2b clinical trial of SYN-010 in the

second half of 2019, anticipated initiation of a Phase 1/2 investigator-sponsored clinical study in HCT patients in 2H 2019, anticipated

increase in research and development expense due to the ongoing Phase 2b investigator-sponsored clinical trial for SYN-010 and

development activities associated with the potential initiation of a Phase 1/2 investigator-sponsored clinical trial for the prevention

of aGVHD in HCT recipients for SYN-004, anticipated filing of a US IND application for SYN-020 in Q4 2019 and plans to commence

a Phase 1 clinical trial for SYN-020 in Q1 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