Synthetic Biologics Reports Third Quarter 2018 Operational Highlights and Financial Results -- Announced Agreement with Cedars-Sinai Medical Center to Co-fund a Phase 2b Investigator-Sponsored Clinical Study of SYN-010,

Synthetic Biologics Reports Third Quarter

2018 Operational Highlights and Financial Results

-- Announced Agreement with Cedars-Sinai

Medical Center to Co-fund a Phase 2b Investigator-Sponsored

Clinical Study of SYN-010, for the Treatment of IBS-C --

-- Strengthened Balance Sheet in Support

of Microbiome-Focused Clinical Development Programs --

-- Conference Call Today, November

8, 2018, at 4:30 p.m. (EST) --

MD, November 8, 2018 - Synthetic Biologics,

Inc. (NYSE American: SYN), a late-stage clinical company developing

therapeutics designed to preserve the microbiome to protect and restore the health of patients, today

provided an operational update and reported financial results for the three and nine months ended September 30,

"During the third quarter, we remained sharply focused on the advancement of our portfolio of microbiome-focused

assets," stated Steven A. Shallcross, Interim Chief Executive Officer and Chief Financial Officer. "We were pleased

to report the expansion of our relationship with Cedars-Sinai Medical Center and announced a research agreement to co-fund an investigator-sponsored

Phase 2b clinical study of SYN-010, our modified-release formulation of lovastatin lactone designed to treat an underlying cause

of irritable bowel syndrome with constipation (IBS-C). In addition to fortifying the well-established clinical data set for SYN-010,

we believe results from this study will determine the optimal dose of SYN-010 for future registration studies. During the third

quarter we also held an End of Phase 2 meeting with the FDA to define a clear and achievable pathway forward for SYN-004, our first-in-class

therapeutic intervention designed to protect the gut microbiome from antibiotic-mediated dysbiosis. We also announced that we are

evaluating opportunities that may further unlock the potential of SYN-004 through the pursuit of a second more focused indication

in a specialty patient population with multiple potential disease endpoints associated with IV beta-lactam-induced gut microbiome

damage, such as allogeneic hematopoietic cell transplant (HCT) recipients. This dual approach may enable us to continue the clinical

advancement of SYN-004 in a cost-effective manner while targeting an area of clear unmet need and expanding upon the established

data set to further validate SYN-004's use in the broader indication for the prevention of CDI."

Mr. Shallcross continued, "While

remaining keenly focused on the execution of our clinical development activities, we also significantly strengthened our balance

sheet by raising gross proceeds of approximately $18.6 million from the closing of a public offering of common stock and Series

B convertible preferred stock, as well as net proceeds of approximately $11.8 million from the utilization of our "at-the-market"

facility through October. As a result of these activities, our current cash position to date is approximately $32 million and

should provide ample runway to allow the Company to continue its operations into 2020 as we continue to focus on the achievement

of key clinical development milestones for our two-lead assets."

Clinical Development and Operational

Quarter Ended September 30, 2018

General and administrative expenses decreased

by 12% to $1.5 million for the three months ended September 30, 2018, from $1.7 million for the three months ended September 30,

2017. This decrease is primarily the result of lower salary expense, stock compensation, and related benefits costs incurred during

the three months ended September 30, 2018 as compared to the three months ended September 30, 2017 due to the resignation of the

prior Chief Executive Officer, along with the reduction of travel and consulting expense, offset by higher registration, investor

relations and legal costs. The charge related to stock-based compensation expense was $186,000 for the three months ended September

30, 2018, compared to $583,000 the three months ended September 30, 2017.

Research and development expenses decreased by 32% to $2.8 million for the three months ended September

30, 2018, from $4.1 million for the three months ended September 30, 2017. This decrease is primarily the result of lower SYN-004

(ribaxamase) and SYN-010 program costs for the three months ended September 30, 2018 since no clinical trials were ongoing during

the quarter. 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 advancement

of these clinical trials. The charge related to stock-based compensation expense was $289,000 for the three months ended September

30, 2018, compared to $317,000 for the three months ended September 30, 2017.

Other income was $631,000 for the three

months ended September 30, 2018, compared to other expense of $5.1 million for the three months ended September 30, 2017. Other

income for the three months ended September 30, 2018 is primarily comprised of non-cash income of $626,000 from the change in fair

value of warrants. The decrease in the fair value of the warrants was due to the decrease in our stock price from the prior quarter.

Cash and cash equivalents as of September

30, 2018 totaled $9.5 million, a decrease of $7.6 million from December 31, 2017, which does not reflect the proceeds from the

sale of our securities during October 2018. During October 2018, we raised gross proceeds of approximately $18.6 million from the

closing of a public offering of common stock and Series B Preferred Stock and received net proceeds of approximately $5.8 million

from sales of our Common Stock in "at-the-market" equity offerings.

Synthetic Biologics will hold a conference

call today, Thursday, November 8,

2018, 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/1096/28046.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/28046,

for 90 days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE American:

SYN) is a late-stage clinical company developing therapeutics designed to preserve the microbiome to protect and restore the health

of patients. The Company's lead candidates poised for Phase 3 development are: (1) SYN-004 (ribaxamase) which is designed to protect

the gut microbiome from the effects of certain commonly used intravenous (IV) beta-lactam antibiotics for the prevention of C.

difficile infection (CDI), overgrowth of pathogenic organisms and the emergence of antimicrobial resistance (AMR), 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 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, and novel discovery stage biotherapeutics for the treatment of phenylketonuria

(PKU). 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 includes statements regarding our belief that results from the investigator-sponsored Phase 2b clinical study of SYN-010 will

determine the optimal dose of SYN-010 for future registration studies, unlocking the potential of SYN-004 through the pursuit of

a second more focused indication in a specialty patient population with multiple potential disease endpoints associated with IV

beta-lactam-induced gut microbiome damage, such as allogeneic hematopoietic cell transplant (HCT) recipients, the dual approach

enabling us to continue the clinical advancement of SYN-004 in a cost-effective manner while targeting an area of clear unmet need

and expanding upon the established data set to further validate SYN-004's use in the broader indication for the prevention

of CDI, the proceeds raised providing ample runway and allowing us to continue our operations into 2020 as we continue to focus

on the achievement of key clinical development milestones for our two-lead assets, anticipated dosing first patient in the Phase

2b investigator sponsored clinical study during Q4 2018, anticipated data readout from the Phase 2b investigator sponsored clinical

study during 2H 2019, plan to initiate clinical trial(s) (2H 2019), anticipated IND filing for SYN-020 during Q4 2019; and the

potential benefits of SYN-004 and SYN-010. 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, , Synthetic Biologics' ability to establish a path forward to develop SYN-010 and ribaxamase and conduct

a robust, controlled and well-designed clinical trial that may provide sufficient efficacy and safety data to support a pathway

towards marketing approval for SYN-010 and ribaxamase, Synthetic Biologics' ability to regain compliance with the continued listing

standards of the NYSE American by September 2, 2019, Synthetic Biologics' ability to comply with other continued listing requirements

of the NYSE American, the ability of its product candidates to demonstrate safety and effectiveness, as well as results that are

consistent with prior results, Synthetic Biologics' clinical trials continuing enrollment as expected, a failure to receive the