Synthetic Biologics Reports Second Quarter 2015 Financial Results and Operational Highlights - Achieved Planned Milestones for Company's Lead Microbiome Drug Candidates - - Enhanced Senior Management Team to Maximize Str

Synthetic Biologics Reports Second Quarter

2015 Financial Results and Operational Highlights

- Achieved Planned Milestones for

Company's Lead Microbiome Drug Candidates -

- Enhanced Senior Management Team

to Maximize Strategic Opportunities -

- Strengthens Balance Sheet to Support

Microbiome Clinical Trials -

- Conference Call Today, August 10,

2015, at 8:30 a.m. EDT -

MD, August 10, 2015 - Synthetic Biologics, Inc.

(NYSE MKT: SYN), a clinical-stage company focused on developing therapeutics to protect the microbiome while targeting pathogen-specific

diseases, reported financial results for the three and six months ended June 30, 2015, and provided an operational update.

"We continue to successfully execute

against our planned milestones and are encouraged by the progress of our two lead microbiome drug candidates," said Jeffrey

Riley, Chief Executive Officer. "We initiated Phase 2a clinical trials for SYN-004, which is designed to protect the gut

microbiome from the effects of certain commonly used intravenous (IV) antibiotics for the prevention of C. difficile infection

and antibiotic-associated diarrhea (AAD). We also initiated a Phase 2 clinical trial for SYN-010 to evaluate the efficacy in reducing

the production of methane in the gut which is perceived as the underlying cause of pain, bloating and constipation associated with

irritable bowel syndrome and constipation (IBS-C)."

Mr. Riley added, "This continued

progress combined with investor interest related to the microbiome enabled us to strengthen our balance sheet with net proceeds

of $42.6 million in a successful July public offering. Our increased cash position provides resources to support our lead microbiome

drug candidates' continued progress in the clinic. And, with the recent additions of industry veterans with proven track

records to our management team, we are better positioned to develop operational and commercial strategies as we navigate through

clinical trials. Looking ahead, we feel confident that we will achieve our milestones and look forward to reporting important microbiome

program developments including, topline data from the two SYN-004 Phase 2a trials and topline data from the first SYN-010 Phase

2 trial. Accomplishing each of these milestones would position us to create value for our shareholders while we work to address

significant unmet medical needs with our novel microbiome drug candidates."

Clinical Program Progress

Prevention of C. difficile infection

TrimestaTM, an oral estriol

drug for the treatment of relapsing-remitting multiple sclerosis (MS) and cognitive dysfunction in MS:

Pertussis (whooping cough) - SYN-005:

Operational Update - Expanded

Three and Six Months Ended June 30,

2015 Financial Results

and administrative expenses increased to $2.2 million and $3.9 million for the three and six months ended June 30, 2015, respectively,

compared to $1.8 million and $2.9 million for the same periods in 2014. The increase of approximately 22% for the three months

ended June 30, 2015 is primarily the result of increased employee costs and legal fees, offset by a decrease in stock-based

compensation expense. The increase of approximately 34% for the six months ended June 30, 2015

is primarily the result of increased employee costs, legal fees and audit fees related to the additional procedures required under

the accelerated filer status. Non-cash charges related to stock-based compensation were $335,000 and $915,000 for the three and

six months ended June 30, 2015, respectively, compared to $645,000 and $899,000 for the same periods in 2014.

Research and development expenses increased

to $7.5 million and $14.0 million for the three and six months ended June 30, 2015, respectively, compared to $2.8 million and

$5.6 million for the same periods in 2014. The increases of approximately 165% and 152% for the three and six months ended June

30, 2015, respectively, are primarily the result of increased program costs associated with expanded clinical development, manufacturing

and research activities for our microbiome-focused pipeline, including the Company's C. difficile and IBS-C programs.

For the six months ended June 30, 2015, research and development expenses also include a $1.0 million expense for achieving the

third milestone as set forth in the Asset Purchase Agreement with Prev ABR LLC, dated November 28, 2012, related to the C. difficile

program. Prev ABR LLC exercised its option to receive the milestone payments in shares of Synthetic Biologics' common stock

that were issued in April 2015. Non-cash charges related to stock-based compensation were $252,000 and $498,000 for the three and

six months ended June 30, 2015, respectively, compared to $210,000 and $318,000 for the same periods in 2014.

Other expense was $3.9 million and $8.0

million for the three and six months ended June 30, 2015, respectively, compared to other income of $95,000 and $96,000 for the

same periods in 2014. Other expense for the three and six months ended June 30, 2015 was primarily the result of a non-cash charge

of $3.9 million and $8.0 million, respectively, related to the change in fair value of warrants due to the increase in the stock

price from the previous quarter. There was no non-cash income or expense relating to fair value warrants for the three and six

months ended June 30, 2014.

cash equivalents at June 30, 2015 was $4.8 million. Subsequent to the end of the second quarter, a public offering was completed

for net proceeds of approximately $42.6 million. The strengthened balance sheet provides the Company with the resources to fund

its clinical development programs.

Synthetic Biologics will hold a conference

call today, Monday, August 10, 2015, at 8:30 a.m. EDT. The dial-in information for the call is as follows: U.S. toll free:

1-888-347-5280 and 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/1096/9809.

An archive of the call will be available for approximately 90 days at the same URL, https://www.webcaster4.com/Webcast/Page/1096/9809,

beginning approximately one hour after the call's conclusion.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN)

is a microbiome-focused, clinical-stage company developing therapeutics to protect the microbiome while targeting pathogen-specific

diseases. The Company's lead candidates in Phase 2 development include SYN-004 which is designed to protect the gut microbiome

from the effects of certain commonly used intravenous (IV) antibiotics for the prevention of C. difficile infection and

antibiotic-associated diarrhea (AAD), and SYN-010 which is intended to reduce the impact of methane producing organisms in the

gut microbiome to treat the underlying cause of irritable bowel syndrome with constipation (IBS-C). In addition, the Company is

developing a Phase 2 oral estriol drug for the treatment of relapsing-remitting multiple sclerosis (MS) and cognitive dysfunction

in MS, and a monoclonal antibody combination for the treatment of Pertussis. For more information, please visit Synthetic Biologics'

website at www.syntheticbiologics.com.

release includes forward-looking statements on Synthetic Biologics' current expectations and projections about future events.

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. These statements are based upon current beliefs, expectations and assumptions and

are subject to a number of risks and uncertainties, many of which are difficult to predict and include statements regarding the

timing of planned Phase 2 clinical trials and expected date of data from clinical trials, continued successful execution against

planned milestones, expected achievement of milestones and impact of achievement of milestones. Important factors that could cause

actual results to differ materially from those reflected in Synthetic Biologics' forward-looking statements 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, to be commenced or completed on

time or to achieve desired results, a failure of Synthetic Biologics' clinical trials to receive anticipated funding, a failure

of Synthetic Biologics' products for the prevention and treatment of diseases to be successfully developed or commercialized,

Synthetic Biologics' inability to maintain its licensing agreements, a failure to successfully integrate new

management and other factors described in Synthetic Biologics' report on Form 10-K for the year ended December 31, 2014 and

any other filings with the SEC. 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: Kris Maly, VP, Corporate

Communication, (734) 332-7800, info@syntheticbiologics.com