Synthetic Biologics Reports Second Quarter 2016 Operational Highlights and Financial Results - Held End of Phase 2 Meeting with FDA and Received Guidance for Advancement to First Pivotal Trial for SYN-010, for the Treatm

Biologics Reports Second Quarter 2016 Operational Highlights and Financial Results

Phase 2 Meeting with FDA and Received Guidance for Advancement to First Pivotal Trial for SYN-010,

of Irritable Bowel Syndrome with Constipation (IBS-C) -

Update on Enrollment for Phase 2b Proof-of-Concept Clinical Trial for SYN-004 (ribaxamase),

of C. Difficile Infection (CDI) and Antibiotic-Associated Diarrhea (AAD) -

- Conference Call Today, August 3,

2016, at 4:30 p.m. EDT -

MD, August 3, 2016 - Synthetic Biologics, Inc.

(NYSE MKT: SYN), a clinical stage company focused on developing therapeutics to protect the gut microbiome while targeting pathogen-specific

diseases, today provided an operational update and reported financial results for the three months ended June 30, 2016.

"In the second quarter we continued

the transition from an early-stage clinical development company to a late-stage clinical development company focused on the commercialization

of our two lead GI microbiome-focused drug candidates," said Jeffrey Riley, Chief Executive Officer. "We held an End

of Phase 2 meeting with FDA and received guidance for advancement to a pivotal clinical trial for SYN-010, designed to treat an

underlying cause of the symptoms associated with irritable bowel syndrome with constipation (IBS-C)." Mr. Riley continued,

"The approval of the generic name ribaxamase' for SYN-004, the announcement of positive clinical outcomes from

a second Phase 2a clinical trial and robust enrollment in our global Phase 2b proof-of-concept clinical trial continued to fuel

momentum for our program designed to protect the gut microbiome and prevent C. difficile infection (CDI), antibiotic-associated

diarrhea (AAD) and the emergence of antibiotic resistant organisms. To date, we have enrolled 374 patients and anticipate announcing

topline results from our ongoing Phase 2b clinical trial for SYN-004 in early 2017."

Microbiome-Focused Clinical Program

SYN-010 - Treatment of irritable

bowel syndrome with constipation (IBS-C):

SYN-004 (ribaxamase) - Prevention of

CDI, AAD and the emergence of antibiotic-resistant organisms:

Operational Update - Expanded

Second Quarter 2016 Financial Results

General and administrative expenses decreased

by 3% to $2.1 million for the second quarter of 2016, from $2.2 million for the second quarter of 2015. This decrease is primarily

the result of lower legal fees offset by an increase in stock-based compensation and increased employee costs associated with the

transition of the administrative and financial office to our Maryland headquarters. The charge related to stock-based compensation

expense was $507,000 for the second quarter of 2016, compared to $335,000 for the second quarter of 2015.

Research and development expenses decreased

by 5% to $7.2 million for the second quarter of 2016, from $7.5 million for the second quarter of 2015. This decrease is primarily

the result of decreased Phase 2 program costs associated with clinical development programs, manufacturing and research activities

within our microbiome-focused pipeline. Research and development expenses also include a charge related to non-cash stock-based

compensation expense of $400,000 for the second quarter of 2016, compared to $252,000 for the second quarter of 2015.

Other income was $3.5 million for the second

quarter of 2016, compared to other expense of $3.9 million for the second quarter of 2015. Other income for the second quarter

of 2016 is due to non-cash expense of $3.5 million from the change in fair value of warrants. The decrease in the fair value of

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

increase of fair value of warrants for the second quarter of 2015 was $3.9 million.

Synthetic Biologics will hold a conference

call today, Wednesday, August 3, 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 and 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/1096/16339.

An archive of the conference call will be available for approximately 90 days at the same URL, https://www.webcaster4.com/Webcast/Page/1096/16339,

beginning approximately one hour after the call's conclusion.

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 (ribaxamase) 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, antibiotic-associated diarrhea (AAD) and the

emergence of antibiotic-resistant organisms. 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 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 the continued transition from

an early-stage clinical development company to a late-stage clinical development company, the continued momentum for Synthetic

Biologics' program designed to protect the gut microbiome and prevent CDI, AAD and the emergence of antibiotic resistant

organisms, the anticipated announcement of topline results from Synthetic Biologics ongoing Phase 2b proof-of-concept clinical

trial of ribaxamase, timing and design of a planned Phase 2b/3 pivotal clinical trial and the results to be achieved from the products.

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, the ability of Synthetic Biologics to successfully design protocols and statistical analysis plans to support the

execution of its trials, 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

For further information, please contact:

Synthetic Biologics, Inc. (Corporate and

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

Caitlin Kasunich, Account Director, (212)

896-1241, ckasunich@kcsa.com

- Financial Tables Follow

Synthetic Biologics, Inc. and Subsidiaries

(in thousands, except share and per

Condensed Consolidated Balance Sheets

Condensed Consolidated Statements of Operations