UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 5)¹

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ý

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

¹ The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 5 to Schedule 13D amends and supplements the Schedule 13D, filed May 29, 2014, as amended by Amendment No. 1, filed June 20, 2014, as amended by Amendment No. 2, filed December 29, 2014, as amended by Amendment No. 3 filed October 16, 2015, as amended by Amendment No. 4 filed February 9, 2017 (the “Original Schedule 13D”), by Phillip Frost, M. D. (“Dr. Frost”) and Frost Gamma Investments Trust (the “Trust” and together with Dr. Frost, the “Filing Persons”) relating to the Common Stock, par value $0.01 per share, of Eloxx Pharmaceuticals, Inc., a Delaware corporation, previously known as “Sevion Therapeutics, Inc.” (the “Issuer”). As of the date of this report, the Filing Persons beneficially own less than 5% of the outstanding shares of the Issuer. Consequently, this Amendment constitutes the final amendment to the Original Schedule 13D and an exit filing for the Filing Persons. Except as set forth herein, this Amendment does not modify any of the information previously reported by the Reporting Persons in the Original Schedule 13D. Unless otherwise indicated, all capitalized terms used herein have the meanings ascribed to them in the Original Schedule 13D.

Item 3 is hereby amended to add the following:

On May 31, 2017, the Issuer, Sevion Sub Ltd., an Israeli company and a wholly-owned subsidiary of the Issuer (“Acquisition Sub”), and Eloxx Pharmaceuticals Ltd., an Israeli company (“Eloxx”), entered into an Agreement, as amended on August 1, 2017 and November 23, 2017 (the “Agreement”), pursuant to which, subject to the satisfaction or waiver of the conditions set forth in the Agreement, Acquisition Sub was to merge with and into Eloxx, with Eloxx as the surviving corporation and a wholly-owned subsidiary of the Issuer (the “Transaction”). The Transaction closed on December 19, 2017, at which time all of the issued and outstanding ordinary and preferred shares of Eloxx stock were converted, on a pro rata basis, into the right to receive 20,316,656 shares of the Issuer’s common stock, after giving effect to the Reverse Stock Split (as defined below). In connection with the Transaction, the Issuer effected a 1-for-20 reverse stock split, effective as of 4:00 pm on December 19, 2017 (the “Reverse Stock Split”), and changed its corporate name to “Eloxx Pharmaceuticals, Inc.” All share amounts contained herein reflect the Reverse Stock Split. Upon closing of the Transaction, pursuant to a subscription agreement by and between the Issuer and the Trust, dated as of May 31, 2017 (the “Subscription Agreement”), the Trust received approximately 497,563 shares of the Issuer. The Agreement was filed as an exhibit to the Issuer’s Current Report on Form 8-K on June 6, 2017, and a form of the Subscription Agreement was filed as an exhibit to the Issuer’s Current Report on Form 8-K on August 3, 2017.

Item 4 is hereby amended to add the following:

The Filing Persons acquired approximately 497,563 shares of Common Stock pursuant to the Subscription Agreement.

Upon closing of the Transaction, Dr. Frost resigned from the Board of Directors of the Issuer, effective December 19, 2017.

Item 5 is hereby amended and restated in its entirety as follows:

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.