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): February 27, 2015

SALIX PHARMACEUTICALS, LTD.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (919) 862-1000

Not Applicable

(Former name or former address, if changed since last report)

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:

Item 8.01 Other Events.

On February 27, 2015, Santarus, Inc., a wholly owned subsidiary of Salix Pharmaceuticals, Ltd. (the “Company”), and Cosmo Technologies Limited (“Cosmo”), the Company’s licensor, commenced a lawsuit against generic drug maker Alvogen Pine Brook, Inc. (“Alvogen”) for Alvogen’s infringement of three patents listed in the U.S. Food and Drug Administration’s (“FDA”) Approved Drug Products with Therapeutic Equivalence Evaluations (commonly known as the “Orange Book”) as covering Uceris^® and its use. This lawsuit was filed within the 45-day response period provided by the Hatch-Waxman Act. The lawsuit was filed in the United States District Court for the District of Delaware.

The Company and Cosmo filed this lawsuit in response to a notice letter, dated January 16, 2015, sent by Alvogen regarding its filing with the FDA of Abbreviated New Drug Application No. 205556 seeking approval for Alvogen to manufacture and sell tablets containing 9 mg of budesonide. This notice letter also stated that ANDA No. 205556 contained Paragraph IV certifications, under 21 U.S.C. Section 355(j) of the Federal Food, Drug, and Cosmetic Act, with respect to all of the patents listed in the Orange Book on that date as covering Uceris^®. The Company and Cosmo are enforcing three of those patents: U.S. Patent Nos. 7,410,651; 8,784,888; and RE43799, and reserve their right to enforce against Alvogen any of the Company’s and Cosmo’s Orange Book listed patents identified by Alvogen in its ANDA. These three patents are all expected to expire on June 9, 2020. The Company remains committed to protecting its intellectual property rights, including its patent protection for Uceris^®.

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.