UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 24, 2013

CEMPRA, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (919)313-6601

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨     Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨     Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨     Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨     Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01. Entry into a Material Definitive Agreement.

Effective May 24, 2013, Cempra, Inc. entered into an agreement with the Biomedical Advanced Research and Development Authority of the U.S. Department of Health and Human Services, or BARDA, for the evaluation and development of our lead product candidate solithromycin for the treatment of bacterial infections in pediatric populations and infections caused by bioterror threat pathogens, specifically anthrax and tularemia.

The agreement is a cost plus fixed fee development contract, with a base performance segment valued at approximately $17.7 million, and four option work segments that BARDA may request in its sole discretion pursuant to the agreement. If all four option segments are requested, the cumulative value of the agreement would be approximately $58 million. Three of the options are cost plus fixed fee arrangements, while the last option is a cost sharing arrangement for which we would be responsible for a designated portion of the costs associated with that work segment. The estimated period of performance for the base performance segment is April 1, 2013 through May 23, 2015. If all option segments are requested, this estimated period of performance would be extended until approximately May 23, 2018.

Activities to be conducted for the base performance include, among other things, toxicology studies, pharmacokinetics and pharmacodynamics studies, safety studies, animal model efficacy studies, and select chemical synthesis activities. In the event that BARDA requests one or more of the option work segments, optional activities to be conducted would include, among other things, additional efficacy studies, Phase 1 and Phase 2/3 clinical studies, dose determination studies and filing of new drug applications.

The description of the agreement with BARDA provided above is qualified in its entirety by reference to the full and complete terms contained in the agreement, which will be filed as an exhibit to our Quarterly Report on Form 10-Q for the quarter ending June 30, 2013.

A copy of the press release announcing the entry into the agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

CEMPRA, INC.

Date: May 28, 2013

/s/ Mark W. Hahn

Mark W. Hahn, Chief Financial Officer