Synthetic Biologics Reports First Quarter 2016 Operational Highlights and Financial Results -- Positioned to Initiate Phase 3 Clinical Trial for SYN-010 for the Treatment of Irritable Bowel Syndrome with Constipation (IB

Synthetic Biologics Reports First Quarter

2016 Operational Highlights and Financial Results

-- Positioned to Initiate Phase 3

Clinical Trial for SYN-010 for the

Treatment of Irritable Bowel Syndrome

with Constipation (IBS-C) in 2H 2016 --

-- Two SYN-010 Posters Scheduled for Presentation

at Digestive Disease Week (DDW 2016),

Including Additional Positive Results

from Two Phase 2 Clinical Trials --

-- Conference Call Today, May 5, 2016,

at 4:30 p.m. (EDT) --

MD, May 5, 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 three months ended March 31, 2016.

"Our momentum from 2015 carried into

the first quarter of 2016, as we continued to make important clinical progress in our microbiome-focused programs. During the quarter,

we announced positive topline results from the second Phase 2 clinical trial of SYN-010 in patients with IBS-C. We are scheduled

to present detailed data supporting previously reported positive topline data from both SYN-010 Phase 2 clinical trials in a poster

presentation at DDW 2016 later this month. We also look forward to holding an end of Phase 2 meeting with the FDA this summer to

discuss late-stage clinical trials of our SYN-010 program," said Jeffrey Riley, President and Chief Executive Officer of

Synthetic Biologics. "With this sustained progress, we are well positioned to initiate Phase 3 clinical trials of SYN-010

during the second half of this year."

Mr. Riley continued, "We've

also made important strides with our program to prevent C. difficile infection and antibiotic-associated diarrhea. Patient

enrollment is complete in the second Phase 2a clinical trial designed to evaluate the GI antibiotic-degrading ability and the safety

of SYN-004 in the presence of a proton pump inhibitor. In addition, patient recruitment in our Phase 2b proof-of-concept clinical

trial for SYN-004 has been strong as we have enrolled approximately 185 patients in this global clinical trial. We look forward

to further progress in our SYN-004 clinical trials and are expecting topline results from the second Phase 2a clinical trial during

the second quarter of 2016 and an interim analysis of blinded data performed by an independent data monitoring committee for the

Phase 2b clinical trial this summer."

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:

Quarter Ended March 31, 2016 Financial

General and administrative expenses were

$2.4 million for the three months ended March 31, 2016, compared to $1.7 million for the same period in 2015. This increase was

primarily the result of increased employee costs associated with the transition of the administrative and financial office to Maryland

headquarters, and increased legal fees and stock-based compensation expense. Non-cash charges related to stock-based compensation

were $643,000 for the three months ended March 31, 2016, compared to $582,000 for the same period in 2015.

Research and development expenses were

$8.2 million for the three months ended March 31, 2016, compared to $6.5 million for the same period in 2015. This increase was

primarily the result of increased Phase 2 program costs associated with expanded clinical development, manufacturing and research

activities within our microbiome-focused pipeline. Non-cash charges related to stock-based compensation were $409,000 for the three

months ended March 31, 2016, compared to $246,000 for the same period in 2015.

Other expense was $497,000 for the three

months ended March 31, 2016, compared to $4.2 million for the same period in 2015. Other expense for the three months ended March

31, 2016 was due to non-cash expense of $498,000 from the change in fair value of warrants. The increase in the fair value of the

warrants was due to the increase in the stock price from the year ended December 31, 2015. Non-cash expense related to fair value

of warrants for the three months ended March 31, 2015 was $4.2 million.

Cash and cash equivalents at March 31,

2016 were $15.1 million, compared to $20.8 million at December 31, 2015.

Synthetic Biologics will hold a conference

call today, Thursday, May 5, 2016, at 4:30 p.m. (EDT). 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/1096/14380.

An archive of the call will be available for replay at the same URL, https://www.webcaster4.com/Webcast/Page/1096/14380,

for 90 days after the call.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN)

is a clinical stage company developing therapeutics to protect the gut microbiome while targeting pathogen-specific diseases.

The Company's lead product 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) beta-lactam antibiotics

for the prevention of C. difficile infection (CDI) and antibiotic-associated diarrhea (AAD). In collaboration with Intrexon

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

pertussis and novel discovery stage biotherapeutics for the treatment of phenylketonuria (PKU). For more information, please visit

Synthetic Biologics' website at www.syntheticbiologics.com.

This press 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 reporting of additional data supporting the previously reported positive topline data from both Phase 2 clinical

trials of SYN-010 at DDW, the reporting of progress in the two ongoing Phase 2 clinical trials for SYN-004, holding an end of Phase

2 meeting with the FDA regarding SYN-010, continued enrollment in Phase 2b proof-of-concept clinical trial for SYN-004 which is

anticipated to enroll up to 370 patients at up to 75 global sites, anticipated interim analysis of blinded data form the Phase

2b trial this summer by an independent data monitoring committee, anticipated reporting of topline results from the second Phase

2a clinical trial of SYN-004 in the second quarter of 2016 and the potential benefits of SYN-004 and SYN-010. These forward-looking

statements are based on management's expectations and assumptions as of the date of this press release and are subject to

a number of substantial risks and uncertainties, many of which are difficult to predict and could cause actual results to differ

materially and adversely from current expectations and assumptions from those set forth, projected 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 that was filed with the U.S. Securities and Exchange Commission (SEC) on March 10, 2016, 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 revise or 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