Synthetic Biologics Announces Exercise of Underwriters’ Over-Allotment Option

ROCKVILLE, Md., Dec. 13, 2013 /PRNewswire/ — Synthetic Biologics, Inc. (NYSE MKT: SYN), a developer of product candidates focused on the prevention and treatment of serious infectious and other diseases, today announced the exercise of the over-allotment option granted to the underwriters to purchase an additional 1,725,000 shares of its common stock, at a price to the public of $1.00 per share, in connection with the Company’s recently announced underwritten public offering of 11,500,000 shares of common stock, bringing total gross proceeds from the offering to $13,225,000, before underwriting discounts and commissions and other offering expenses payable by the Company.

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Aegis Capital Corp. is acting as sole book-running manager for the offering.

This offering was made only by means of a prospectus. Copies of the prospectus relating to this offering may be obtained by contacting Aegis Capital Corp., Prospectus Department, 810 Seventh Avenue, 18th Floor, New York, New York 10019, telephone: 212-813-1010, e-mail: prospectus@aegiscap.com.

A registration statement relating to these securities was declared effective by the Securities and Exchange Commission on July 16, 2013. This press release shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN) is a biotechnology company focused on the development of product candidates for serious infectious and other diseases. Synthetic Biologics is developing oral treatments targeting archaea, a non-bacterial intestinal form of life increasingly associated with chronic diseases such as irritable bowel syndrome (IBS), obesity and type 2 diabetes, an oral biologic to protect the gastrointestinal microflora from the effects of IV antibiotics for the prevention of C. diff infection, a series of monoclonal antibodies (mAbs) for the treatment of Pertussis and Acinetobacter infections, and a biologic targeted at the prevention and treatment of IBS. In addition, the Company is developing an oral estriol drug candidate for the treatment of relapsing-remitting multiple sclerosis (MS) and cognitive dysfunction in MS (with results of an ongoing 164 subject, 15 center, two-year, double blind, placebo controlled, Phase II relapsing-remitting MS clinical trial expected to be announced during the first half of 2014). For more information, please visit Synthetic Biologics’ website at www.therivabio.com.

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements reflect management’s current expectations, as of the date of this press release, and involve certain risks and uncertainties. Forward-looking statements include statements herein with respect to this offering and the successful execution of the Company’s business strategy, including with respect to the Company’s research and development and clinical evaluation efforts. The Company’s actual results could differ materially from those anticipated in these forward-looking statements as a result of various factors. Factors that could cause future results to materially differ from the recent results or those projected in forward-looking statements include the “Risk Factors” described in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on April 16, 2013 and in the Company’s periodic filings with the SEC. The Company’s further development is highly dependent on future medical and research developments and market acceptance, which is outside its control.

SOURCE Synthetic Biologics, Inc.