Synthetic Biologics Reports 2015 Year End Operational Highlights and Financial Results -- Reported Positive Topline Data from Phase 2 Clinical Trials of SYN-010 for Irritable Bowel Syndrome with Constipation and SYN-004

Synthetic Biologics Reports 2015 Year

End Operational Highlights and Financial Results

-- Reported Positive Topline Data

from Phase 2 Clinical Trials of SYN-010 for Irritable Bowel Syndrome

with Constipation and SYN-004 for Prevention of C. difficile

Infection and Antibiotic-Associated Diarrhea --

-- Expect to Initiate Phase 3 Clinical

-- Conference Call Today, March 10,

2016, at 4:30 p.m. (EST) --

MD, March 10, 2016 - Synthetic Biologics, Inc. (NYSE MKT: SYN), a clinical

stage company focused on developing therapeutics to protect the gut microbiome, today provided

an operational update and reported financial results for the year ended December 31, 2015.

"2015 was a milestone year for Synthetic

Biologics. We made important clinical progress in our lead microbiome-focused programs, including the announcement of positive

topline results from the second Phase 2 clinical trial for SYN-010 which demonstrated statistical significance in both primary

and secondary endpoints in patients suffering from irritable bowel syndrome with constipation (IBS-C)," said Jeffrey Riley,

President and Chief Executive Officer Synthetic Biologics. "We also reported positive topline results from the first Phase

2a clinical trial demonstrating that SYN-004 successfully degraded residual intravenous (IV) ceftriaxone in study participants

without affecting the intended level of antibiotic in the bloodstream."

Mr. Riley concluded, "We anticipate

continued momentum in the clinic during 2016 and look forward to reporting progress in two ongoing Phase 2 clinical trials for

SYN-004, including topline data from the second Phase 2a clinical trial and an interim analysis of blinded data by an independent

monitor committee for the Phase 2b proof-of-concept global study in the first half of 2016. Of significant importance during 2016

is scheduling an end of Phase 2 meeting with the FDA regarding the SYN-010 IBS-C program, and our plans to initiate Phase 3 clinical

trials during the second half of the year."

Microbiome-Focused Clinical Program

SYN-010 - Treatment of irritable

bowel syndrome with constipation (IBS-C):

SYN-004 - Prevention of C.

difficile infection (CDI), antibiotic-associated diarrhea (AAD) and emergence of antibiotic-resistant organisms:

Year Ended December 31, 2015 Financial

General and administrative expenses were

$8.1 million for the year ended December 31, 2015, compared to $6.0 million for the same period in 2014. This increase was primarily

the result of increased employee costs, audit fees related to additional procedures required under the accelerated filer status,

legal fees associated with SEC filings and collaborative agreements, and stock-based compensation expense. Non-cash charges related

to stock-based compensation were $2.1 million for the year ended December 31, 2015, compared to $1.6 million for the same period

and development expenses increased to $32.9 million for the year ended December 31, 2015, from $14.5 million for the same period

in 2014. This increase of 127% was primarily the result of increased program costs associated with expanded clinical development,

manufacturing and research activities within our microbiome-focused pipeline, including the Company's Phase 2 C. difficile

and IBS-C clinical programs. In August 2015, Synthetic Biologics entered into an Exclusive Channel Collaboration (ECC) with

Intrexon Corporation for the development of a treatment for patients with phenylketonuria (PKU) and issued 937,500 shares of common

stock to Intrexon as payment of the technology access fee, which resulted in a non-cash charge of $3.0 million. Research and development

expenses also included a $1.0 million non-cash expense for achieving the third milestone set forth in the Prev ABR LLC agreement

with regard to the Company's C. difficile program. Non-cash charges related to stock-based

compensation were $1.1 million for the year ended December 31, 2015, compared to $803,000 for the same period in 2014.

Other income was $3.8 million for the year

ended December 31, 2015, compared to other income of $718,000 for the same period in 2014. Other expense for the year ended December

31, 2015 was primarily due to non-cash expense of $3.8 million from the change in fair value of warrants. The increase in fair

value of the warrants was due to the increase in our stock price from the year ended December 31, 2014.

Cash at December 31, 2015 was $20.8 million

compared to $17.5 million at December 31, 2014.

Synthetic Biologics will hold a conference

call today, Thursday, March 10, 2016, at 4:30 p.m. (EST). 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/1096/13874.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/13874, for 60

days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN)

is a clinical stage company developing therapeutics to protect the microbiome while targeting pathogen-specific diseases. The Company's

lead candidates in Phase 2 development are: (1) 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) and (2) 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). In collaboration with Intrexon Corporation (NYSE: XON),

the Company is also developing preclinical stage monoclonal antibody therapies for the prevention and treatment of Pertussis and

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 include statements regarding the expected initiation of Phase 3 clinical trials for SYN-010 and SYN-004 and the timing of the

initiation, the anticipated continued momentum in the clinic during 2016, the reporting of progress in the two ongoing Phase 2

clinical trials for SYN-004, the scheduling of an end of Phase 2 meeting with the FDA regarding SYN-010, continued enrollment in

Phase 2b proof-of-concept clinical trial for SYN-010, anticipated enrollment of 370 patients at up to 75 global sites, anticipated

interim analysis of blinded data by an independent monitor committee in the first half of 2016, continued enrollment in the second

Phase 2a clinical trial of SYN-004, anticipated reporting of topline results from the Phase 2a clinical trial of SYN-004 in the

first half of 2016 and the potential benefits of SYN-004 and SYN-010. These forward-looking statements are based 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, 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,

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 and other factors described

in Synthetic Biologics' most recent Form 10-K 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 law.

For further information, please contact:

Synthetic Biologics, Inc. (Corporate and

Kris Maly, Vice President, Corporate Communication,

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

Vincent I. Perrone, Manager, Corporate

Communication, (240) 660-2000, info@syntheticbiologics.com

KCSA Strategic Communications (Media)

Lewis Goldberg, Managing Partner, (212)

896-1216, lgoldberg@kcsa.com