Synthetic Biologics Reports Second Quarter 2013 Financial Results and Operational Update -- Progress Cited On Three Infectious Disease Programs, Including Two Programs in Collaboration with Intrexon Corporation; C. diffi

Synthetic Biologics Reports Second Quarter

2013 Financial Results and Operational Update

-- Progress Cited On Three Infectious

Disease Programs, Including Two Programs in Collaboration

with Intrexon Corporation; C.

difficile Prophylactic is Lead Anti-Infective Candidate --

Rockville, MD, August 14, 2013 -

Synthetic Biologics, Inc. (NYSE MKT: SYN), a developer of biologics focused on the prevention and treatment of serious infectious

diseases, today reported financial results for the three and six months ended June 30, 2013 and provided an operational update.

development portfolio includes three anti-infective product candidates, two of which are being developed in collaboration with

Intrexon Corporation (NYSE: XON), and an oral multiple sclerosis (MS) product candidate in Phase II development. The relapsing-remitting

MS clinical trial is expected to be completed in January 2014, with key data to be released shortly thereafter.

call scheduled for 4:00pm EDT today. To participate, please call

1-800-860-2442 (U.S. toll free), 1-866-605-3852

(Canada), or +1 412-858-4600 (International),

fifteen minutes before the start of

the call to register. The call will also be webcast over the Internet at

http://www.videonewswire.com/event.asp?id=95523.

"Our lead anti-infective candidate

SYN-004 for the prevention of C. difficile (C. diff) infections, is a second generation compound designed to address a broader

population than its predecessor, which successfully completed a proof-of-concept Phase II study in Europe," said Jeffrey

Riley, Synthetic Biologics' CEO. "Manufacturing of SYN-004 is underway, and with completion of that we will be able

to commence toxicology bridging studies, followed by the start of clinical trials in 2014."

"In addition, we are making excellent

progress in our collaboration with Intrexon for antibody programs, which currently covers treatment candidates for Pertussis

and Acinetobacter infections. We expect to initiate IND-enabling studies of our Pertussis candidate before year end,"

Mr. Riley continued, "In developing

and interlinking cutting edge cellular technologies for a broad range of applications as Intrexon does, an antibody discovery platform

has been created that is powered to yield novel molecular entities intended to treat diseases for which current therapies are inadequate.

Our collaboration with Intrexon is a prime example of how two innovative companies can work together to pursue significant medical

C. diff and Acinetobacter candidates may qualify for expedited review programs at the FDA for the treatment

of serious conditions with unmet medical needs, such as are addressed by the GAIN Act. The expedited

programs established by the FDA not only point to the urgency for new medications for devastating

diseases, but also potentially shorten the time to market," concluded Mr. Riley.

The Company's core competencies in

anti-infectives have been strengthened with the recent appointment of industry veteran Lewis Barrett to the post of Senior Vice

President, Commercial Strategy. Mr. Barrett was formerly Assistant Vice President, Established Products at Pfizer and Vice President

Global Business Manager, Infectious Diseases at Wyeth Pharmaceuticals.

Operational Highlights

SYN-004 Product Candidate for Point-of-Care

Prevention for C. diff Infections

"We believe SYN-004 is a breakthrough

candidate within a market where no approved prophylactic for C. diff currently exists," Mr. Riley noted. "As

strange as it may seem, the only treatments available to patients are more antibiotics or fecal transplantation."

Monoclonal Antibody (mAb) Programs

in Collaboration with Intrexon Corporation

Phase II Study of MS Candidate, Trimesta

Three and Six Months Ended June 30,

2013 Financial Results

General and administrative expenses were

$1.3 million and $2.4 million for the three and six months ended June 30, 2013, respectively, compared to $1.2 million and $2.6

million for the same periods in 2012. The decrease of 10% for the six month period ended June 30, 2013 is primarily the result

of decreased outside legal and consulting fees. Non-cash charges related to stock-based compensation were $299,000 and $652,000

for the three and six months ended June 30, 2013, respectively, compared to $287,000 and $786,000 for the same periods in 2012.

Research and development expenses were

$1.2 million and $2.3 million for the three and six months ended June 30, 2013, respectively, compared to $547,000 and $933,000

for the same periods in 2012. These increases of 120% and 149%, respectively, are primarily the result of additional employee costs

and increased program costs associated with our infectious disease programs. Non-cash charges related to stock-based compensation

were $109,000 and $212,000 for the three and six months ended June 30, 2013, respectively, compared to $113,000 and $122,000 for

the same periods in 2012.

Other expense was $36,000 for the three

months ended June 30, 2013, compared to other income of $7,000 for the same period in 2012. Other expense was $24,000 for the six

months ended June 30, 2013, compared to other income of $12,000 for the same period in 2012.

Cash at June 30, 2013 was $6.9 million

compared to $10.0 million at December 31, 2012.

Synthetic Biologics will hold a conference

call today, Wednesday, August 14, 2013, at 4:00 pm EDT. During the call, Jeffrey Riley,

Synthetic Biologics' Chief Executive Officer, will provide a brief update of the Company's MS clinical program and

its infectious disease pipeline, including its oral enzyme candidate for the prevention of C. diff infections and monoclonal

antibody candidates for the treatment of Pertussis and Acinetobacter infections. Evan Ballantyne, Synthetic Biologics'

Chief Financial Officer, will review the Company's financial results for the second quarter ended June 30, 2013.

Interested parties should call 1-800-860-2442

(U.S. toll free), 1-866-605-3852 (Canada), or +1 412-858-4600 (International), fifteen minutes before the start of the call to

register. Registered callers on the toll free line may ask to be placed in the queue for the Question & Answer Session. The

call will also be webcast over the Internet at http://www.videonewswire.com/event.asp?id=95523.

If you are unable to participate during the live conference call, the webcast will be available for replay at the same URL, http://www.videonewswire.com/event.asp?id=95523

for 30 days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics (NYSE MKT: SYN) is

a biotechnology company focused on the development of biologics for the prevention and treatment of serious infectious diseases.

The Company is developing an oral enzyme for the prevention of C. difficile infections, and a series of monoclonal antibody

therapies for the treatment of Pertussis and Acinetobacter infections. In addition, the Company is developing a

drug candidate for the treatment of relapsing-remitting multiple sclerosis and cognitive dysfunction in multiple sclerosis. For

more information, please visit Synthetic Biologics' website at www.syntheticbiologics.com.

To download Synthetic Biologics'

investor relations mobile device app, which allows users access to the Company's SEC documents, press releases and events, please

click on the following links to download the IRapp on your iPhone and iPad or your Android

Copaxone is a registered trademark

of Teva Pharmaceutical Industries Ltd.

This 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 advancing our clinical programs,

the opportunities and our position in the infectious disease market, the anticipated contributions of Lewis Barrett, the anticipated

timing and results of our development efforts and the expected size of the future market for sales of therapies for C. difficile

infection, Pertussis and Acinetobacter. The forward-looking statements are subject to risks and uncertainties that could cause

actual results to differ materially from those set forth or implied by any forward-looking statements. Important factors that could

cause actual results to differ materially from those reflected in Synthetic Biologics' forward-looking statements include,