Synthetic Biologics Reports Second Quarter 2018 Operational Highlights and Financial Results - SYN-004 End of Phase 2 Meeting with U.S. Food & Drug Administration on Track for Third Quarter of 2018 - - Conference Call To

Synthetic Biologics Reports Second Quarter

2018 Operational Highlights and Financial Results

- SYN-004 End of Phase 2 Meeting

with U.S. Food & Drug Administration on Track for Third Quarter of 2018 -

- Conference Call Today, August 8,

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

Rockville, MD, August 8, 2018 - Synthetic Biologics, Inc. (NYSE American: SYN), a late-stage

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

an operational update and reported financial results for the three months ended June 30, 2018.

"Following several productive meetings

earlier this year, we are pleased to have reached preliminary agreement on key elements of our planned Phase 3 clinical trial for

ribaxamase, our first-in-class therapeutic intervention designed to prevent the onset of primary C. difficile infection

(CDI) by protecting the gut microbiome from antibiotic-mediated dysbiosis. We are in the process of optimizing a protocol synopsis

for the Phase 3 clinical trial which we will discuss with the FDA at our end of Phase 2 meeting which is currently planned to take

place towards the end of the third quarter" stated Steven A. Shallcross, Interim Chief Executive Officer and Chief Financial

"We will continue to work closely

and collaboratively with the FDA to define a clear and achievable pathway toward gaining marketing approvals. In our ongoing interactions

with FDA, what has become clear is their recognition of the unmet need for novel interventions to combat and prevent the proliferation

of CDI. With more than 450,000 cases of CDI each year in the U.S., if approved, ribaxamase will be the first intervention specifically

designed to prevent CDI associated with the most commonly used IV antibiotics," concluded Shallcross.

Clinical Development and Operational

Quarter Ended June 30, 2018 Financial

General and administrative expenses

decreased by 13% to $1.4 million for the three months ended June 30, 2018, compared to $1.6 million for the same period in

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

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

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 $264,000 for the three months ended

June 30, 2018, compared to $539,000 for three months ended June 30, 2017.

Research and development expenses decreased

by 25% to $3.6 million for the three months ended June 30, 2018, from $4.8 million for the three months ended June 30, 2017. This

decrease is primarily the result of lower SYN-004 (ribaxamase) and SYN-010 program costs for 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 seek to secure the financial resources necessary for

the completion of these clinical trials. The charge related to stock-based compensation expense was $293,000 for the three months

ended June 30, 2018, compared to $331,000 for the same period in 2017.

Other income was $789,000 million for the

three months ended June 30, 2018, compared to other income of $2.2 million for the same period in 2017. Other income for the three

months ended June 30, 2018 is primarily comprised of non-cash income of $783,000 million 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 June 30,

2018 was $7.1 million, a decrease of $10.0 million from December 31, 2017.

Synthetic Biologics will hold a conference

call today, Tuesday, August 8, 2018, at 4:30 p.m. (EDT). 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/1096/26414.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/26414, for 90

days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE American:

SYN) is a late-stage clinical company developing therapeutics that 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 plan to continue to work closely with the FDA to define a clear and achievable pathway toward gaining market

approval, expectations as to the elements of the proposed Phase 3 clinical trial for SYN-004; the anticipated timing of the

initiation of the end of Phase 2 meeting, which is anticipated to be held during the end of the third quarter of 2018; the

plan to initiate SYN-004 Phase 3 clinical trial in 2H 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 design a Phase 3 trial with the co-primary endpoints and receive FDA approval

for such design; Synthetic Biologics' ability to implement the Phase 3 program as a global, event-driven clinical

trial, Synthetic Biologics' ability to initiate the Phase 3 clinical program in the second half of 2019 following an

end of Phase 2 meeting with the FDA during the third quarter of 2018, Synthetic Biologics' ability to establish a path

forward to develop 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 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 necessary regulatory approvals

for commercialization of Synthetic Biologics' therapeutics, including approval of proposed trial designs, 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, Synthetic Biologics' ability

to achieve acceptance of its product candidates in the marketplace and the successful development, marketing or sale of

Synthetic Biologics' products by competitors that render Synthetic Biologics' products obsolete or

non-competitive, the continued maintenance and growth of Synthetic Biologics' patent estate, Synthetic Biologics

becoming and remaining profitable, Synthetic Biologics' ability to obtain or maintain the capital or grants necessary

to fund its research and development activities, a loss of any of Synthetic Biologics' key scientists or management

personnel and other factors described in Synthetic Biologics' Form 10-K for the year ended December 31, 2017 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

For further information, please contact:

Synthetic Biologics, Inc. (Corporate and

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