Synthetic Biologics Reports Year End

Synthetic Biologics Reports Year End

2012 Financial Results

-- Strengthening Infectious Disease

Portfolio to Include C. difficile, Pertussis and Acinetobacter Targets --

Rockville, MD, April 16, 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 year ended December 31, 2012 and summarized recent operational highlights.

Operational Highlights:

Expanding Infectious Disease Portfolio

Ongoing Phase II Multiple Sclerosis

(MS) Clinical Trials

Corporate Highlights:

Completed Successful Capital Raise

"During 2012, we targeted our resources

toward strengthening our infectious disease portfolio, specifically to address the increasing need for therapies to prevent and

treat infections caused by C. difficile, Pertussis and Acinetobacter. We believe there is a major void in the market

when it comes to developing such therapies, mainly due to these bacteria becoming immune to current antibiotics and the evolving

strains of bacteria that are often stronger," said Jeffrey Riley, Chief Executive Officer of Synthetic Biologics.

"We are excited about our opportunity

to develop a novel therapy to prevent C. difficile infections. The highly-experienced Synthetic Biologics' team is

driving the C. difficile program toward the clinic. In addition, we are working with Intrexon's comprehensive suite

of proprietary technologies to move our promising early-stage programs for the treatment of Pertussis and Acinetobacter

infections forward. We are committed to building a strong public presence and dedicate ourselves to the virtually untapped infectious

disease market," concluded Mr. Riley.

Year Ended December 31, 2012 Financial Results

As part of management's plan to streamline

our focus, we sold the clinical reference lab on March 8, 2012. Laboratory revenues for the years ended December 31, 2012 and December

31, 2011 were charged to discontinued operations, resulting in no revenues for these periods. In addition, the gain on the sale

of the clinical reference lab of $677,000 was included in discontinued operations for the year ended December 31, 2012.

General and administrative expenses increased

to $5.0 million for the year ended December 31, 2012, compared to $2.6 for the same period in 2011. The increase of 94% is primarily

the result of additional employee costs, the expansion of our investor relation activities and legal fees. Charges related to stock-based

compensation were $1.5 million for the year ended December 31, 2012, compared to $919,000 for the same period in 2011.

Research and development expenses were

$12.3 million for the year ended December 31, 2012, compared to $3.3 million for the same period in 2011. The increase of 268%

is primarily the result of recording the fair value of the common stock issued to Intrexon as consideration for the infectious

disease collaboration ($7.8 million) and the fair value of the common stock issued for the acquisition of the C. difficile

program assets ($1.2 million). Charges related to stock-based compensation were $400,000 for the year ended December 31, 2012,

compared to $54,000 for the same periods in 2011.

Other income was $15,000 for the year ended

December 31, 2012, compared to other expense of $1.7 million for the same period in 2011. Other expense for the year ended December

31, 2011 related to the estimated fair value of the warrants associated with the January 2011 and April 2011 financings, adjusted

for the change in their fair value at December 31, 2011.

Cash as of December 31, 2012 was $10.0

million compared to $6.7 million as of December 31, 2011. As of March 27, 2013, our cash balance was approximately $8.7 million.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (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.

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 our continued focus of our

efforts in the field of synthetic biology and advancing our clinical programs, the opportunities in the infectious disease market,

the anticipated results of our development efforts and the expected size of the future market for sales of therapies for CDI ,

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, among others,

a failure to receive the necessary regulatory approvals for commercialization of our therapeutics, a failure of our clinical trials

to be commenced or completed on time or to achieve desired results, a failure of our clinical trials to receive anticipated funding,

a failure of our monoclonal antibodies for the treatment of infectious diseases to be successfully developed or commercialized,

our inability to maintain our licensing agreements, including our agreements with Intrexon, our inability to successfully integrate

new management, or a failure by us or our strategic partners to successfully commercialize products and other factors described

in Synthetic Biologics' report on Form 10-K for the year ended December 31, 2012 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

-- Financial Tables to Follow--

For further information, please contact:

Vice President, Corporate Communication

(734) 332-7800, Ext. 22