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 26, 2020

ACELRX PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

351 Galveston Drive

Redwood City, CA 94063

(Address of principal executive offices and zip code)

Registrant’s telephone number, including area code: (650) 216-3500

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 (see General Instruction A.2. below):

Securities registered pursuant to Section 12(b) of the Act

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Amendment No. 2 to Merger Agreement

On May 29, 2020, AcelRx Pharmaceuticals, Inc., a Delaware corporation (“AcelRx”), Tetraphase Pharmaceuticals, Inc., a Delaware corporation (“Tetraphase”), and Consolidation Merger Sub, Inc., a Delaware corporation and an indirect wholly-owned subsidiary of AcelRx (“Merger Sub”), entered into an amendment (the “Second Amendment”) to the Agreement and Plan of Merger dated March 15, 2020 (as amended by the Amendment to Agreement and Plan of Merger, dated May 27, 2020 (“Amendment No. 1”), by and among AcelRx, Tetraphase and Merger Sub, the “Merger Agreement”). Pursuant to the Merger Agreement, as amended by the Second Amendment, Merger Sub will be merged with and into Tetraphase (the “Merger”), with Tetraphase continuing as the surviving corporation and an indirect wholly-owned subsidiary of AcelRx.

Pursuant to the Second Amendment, AcelRx and Tetraphase have agreed to further amend the terms of the Merger Agreement to provide that, among other things:

The Tetraphase board of directors has approved the Merger and the amended terms of the Merger in the Second Amendment, has determined that, as a result of the Second Amendment, the proposal received by Tetraphase from Melinta Therapeutics, Inc. on May 27, 2020 is not superior and has recommended the adoption of the Merger Agreement, as amended by the Second Amendment, by the Tetraphase stockholders.

The foregoing description of the Second Amendment does not purport to be complete and is qualified in its entirety by reference to the full text of the Second Amendment, which is filed as Exhibit 2.1 to this Current Report on Form 8-K and is incorporated herein by reference. Other than as expressly modified pursuant to the Second Amendment, the Merger Agreement remains in full force and effect.

The Second Amendment and the foregoing description of the Second Amendment have been included to provide investors and stockholders with information regarding its terms. The representations and warranties contained in the Second Amendment were made only for the purposes of the Second Amendment as of specific dates, are solely for the benefit of the parties, and may have been qualified by certain disclosures between the parties and a contractual standard of materiality different from those generally applicable to investors or stockholders, among other limitations. The representations and warranties were made for the purposes of allocating contractual risk among the parties to the Second Amendment and should not be relied upon as a disclosure of factual information relating to AcelRx or Tetraphase. Moreover, information concerning the subject matter of the representations, warranties and covenants may change after the date of the Second Amendment, which subsequent information may or may not be fully reflected in public disclosures.

Revised Form of Contingent Value Rights Agreement

In connection with the Second Amendment, AcelRx and Tetraphase also agreed to a revised form of Contingent Value Rights Agreement (the “Revised CVR Agreement”), which will govern the terms of the CVRs and will be entered into at or prior to the Effective Time. Pursuant to the Revised CVR Agreement, the CVRs now represent an aggregate right to receive up to $16.0 million in cash, without interest and less any applicable withholding taxes, in contingent consideration, conditioned upon the achievement of specified levels of annual net sales of XERAVA as follows:

The terms of the CVRs described above reflect the parties’ agreement over the sharing of potential economic upside benefits from future net sales of XERAVA and do not necessarily reflect anticipated net sales of XERAVA. There can be no assurance that such levels of net sales will occur or that any or all of the payments in respect of the CVRs will be made.

The right to such contingent consideration as evidenced by the Revised CVR Agreement is a contractual right only and will not be transferable, except in the limited circumstances specified in the Revised CVR Agreement. The foregoing description of the Revised CVR Agreement does not purport to be complete and is qualified in its entirety by reference to the form of Revised CVR Agreement, which is filed as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Amendment to Voting Agreement

In connection with the execution of the Second Amendment, AcelRx and certain stockholders of Tetraphase representing approximately 20% of the voting power of Tetraphase entered into separate amendments (each such amendment, “Amendment No. 2 to Voting Agreement”) to the Voting Agreements, dated March 15, 2020, and amended by the Amendment to Voting Agreement entered into in connection with the execution of Amendment No. 1 (“Amendment No. 1 to Voting Agreement”), by and between AcelRx, Merger Sub and each such stockholder (such Voting Agreements, as amended by Amendment No. 1 to Voting Agreement and Amendment No. 2 to Voting Agreement, the “Amended Voting Agreements”). Pursuant to the Amended Voting Agreements, each such stockholder agreed to, among other things, vote the shares of Tetraphase common stock beneficially owned by such stockholder in favor of the adoption of the Merger Agreement, as amended by the Second Amendment, and against any acquisition proposal or liquidation or dissolution of Tetraphase, as well as such other matters set forth in the Amended Voting Agreement.

Pursuant to the Amended Voting Agreement, each such stockholder that is a party thereto has also agreed to (i) exchange certain outstanding Tetraphase common stock warrants for a fixed amount of cash consideration and number of shares of AcelRx common stock and (ii) exchange certain outstanding Tetraphase pre-funded common stock warrants for a specified percentage of the Merger Consideration.

The foregoing description of Amendment No. 2 to Voting Agreement does not purport to be complete and is qualified in its entirety by reference to the form of Amendment No. 2 to Voting Agreement, which is filed as Exhibit 10.2 to this Current Report on Form 8-K and is incorporated herein by reference. Other than as expressly modified pursuant to Amendment No. 1 to Voting Agreement and Amendment No. 2 to Voting Agreement, the Voting Agreements, a form of which was filed as Exhibit 10.2 to the Current Report on Form 8-K filed with the SEC by AcelRx on March 16, 2020, remain unchanged.

Amendment No. 1 to Co-Promotion Agreement

Separate and distinct from the Merger Agreement and the Second Amendment, on May 26, 2020, AcelRx and Tetraphase entered into Amendment No. 1 to Co-Promotion Agreement (the “Co-Promotion Amendment”) to specify certain work level efforts to address the impact of the Covid-19 pandemic.

The foregoing description of the Co-Promotion Amendment does not purport to be complete and is qualified in its entirety by reference to the Co-Promotion Amendment, which is filed as Exhibit 10.3 to this Current Report on Form 8-K and is incorporated herein by reference.

On May 29, 2020, AcelRx issued a press release announcing the entry into the Second Amendment. A copy of the press release is attached as Exhibit 99.1 and is incorporated by reference herein.

(d) Exhibits

The following exhibits are filed herewith:

Forward-Looking Statements

This Current Report on Form 8-K may contain forward-looking statements, including, but not limited to, statements relating to AcelRx’s intentions, plans, hopes, beliefs, anticipations, expectations or predictions of the future, or statements relating to the consummation of the proposed transaction and the other transactions described above and the potential benefits of such transactions. These statements may be identified by the use of forward-looking terminology such as “believes,” “expects,” “anticipates,” “may,” “will,” “should,” “seeks,” “approximately,” “intends,” “plans,” “estimates,” or the negative of these words or other comparable terminology. These forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those projected, anticipated or implied by such statements, including the risk AcelRx may not be able to close the acquisition of Tetraphase or achieve the expected benefits and cost synergies from the transactions, that actions taken by competing bidders for Tetraphase or fluctuations in the market price of AcelRx’s common stock could delay or prevent the consummation of the proposed transaction, or that the impacts AcelRx is experiencing from the ongoing COVID-19 pandemic may be prolonged or exacerbated. In addition, such risks and uncertainties may include, but are not limited to, those described in AcelRx’s annual, quarterly and current reports (i.e., Form 10-K, Form 10-Q and Form 8-K) as filed or furnished with the SEC. You are cautioned not to place undue reliance on any such forward-looking statements, which speak only as of the date such statements were first made. AcelRx’s SEC reports are available at www.acelrx.com under the “Investors” tab. Except to the extent required by law, AcelRx undertakes no obligation to publicly release the result of any revisions to these forward-looking statements to reflect events or circumstances after the date hereof, or to reflect the occurrence of unanticipated events.

Additional Information and Where to Find It

In connection with the proposed transaction between AcelRx and Tetraphase, AcelRx has filed with the SEC a registration statement on Form S-4 (No. 333-237584) (the “Registration Statement”) containing a document constituting a prospectus of AcelRx and a proxy statement of Tetraphase. The Registration Statement was declared effective by the SEC on April 24, 2020, and Tetraphase mailed the definitive proxy statement/prospectus to the stockholders of Tetraphase on or about April 28, 2020. AcelRx and Tetraphase also plan to file other relevant documents with the SEC regarding the proposed transaction. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT/PROSPECTUS AND OTHER RELEVANT DOCUMENTS FILED OR THAT WILL BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY CONTAIN IMPORTANT INFORMATION. Investors and security holders are or will be able to obtain free copies of the Registration Statement and the definitive proxy statement/prospectus and other relevant documents filed or that will be filed by AcelRx or Tetraphase with the SEC through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed with the SEC by AcelRx are available free of charge within the Investors section of AcelRx’s website at http://ir.acelrx.com. Copies of the documents filed with the SEC by Tetraphase are available free of charge within the Investors section of Tetraphase’s website at https://ir.tphase.com/investor-relations.

Participants in the Solicitation

Each of AcelRx and Tetraphase and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from Tetraphase stockholders in connection with the proposed transaction. Information about AcelRx’s directors and executive officers is included in the definitive proxy statement for its 2020 annual meeting of stockholders, which was filed with the SEC on April 24, 2020. Information about Tetraphase’s directors and executive officers is included in Tetraphase’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019, which was filed with the SEC on March 12, 2020. Other information regarding the participants in the solicitation of proxies in connection with the proposed transaction and a description of their direct and indirect interests, by security holdings or otherwise, is contained in the definitive proxy statement/prospectus filed with the SEC on April 24, 2020, as amended. Investors may obtain free copies of these documents from AcelRx or Tetraphase as indicated above.

No Offer or Solicitation

This communication is being made in respect of the proposed transaction involving AcelRx and Tetraphase. This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities nor a solicitation of any vote or approval with respect to the proposed transaction or otherwise. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended, and otherwise in accordance with applicable law.

SIGNATURES

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