EX(a)(1)(iv)

THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME,

AT THE END OF THE DAY ON DECEMBER 16, 2015, UNLESS THE OFFER IS EXTENDED OR EARLIER TERMINATED.

Zanzibar Acquisition Corp., a Delaware corporation (“Purchaser”) and a wholly owned subsidiary of Zeneca, Inc., a Delaware corporation (“Parent”), is making an offer to purchase all outstanding shares of common stock, par value $0.001 per share (the “Shares”), of ZS Pharma, Inc., a Delaware corporation (“ZS Pharma”), at a purchase price of $90.00 per Share (the “Offer Price”), net to the seller in cash, without interest, subject to any required withholding of taxes and upon the terms and subject to the conditions set forth in the Offer to Purchase dated November 18, 2015 (as it may be amended or supplemented from time to time, the “Offer to Purchase”) and the related Letter of Transmittal (as it may be amended or supplemented from time to time, the “Letter of Transmittal” and, together with the Offer to Purchase, the “Offer”) enclosed herewith.

Please furnish copies of the enclosed materials to those of your clients for whose accounts you hold Shares registered in your name or in the name of your nominee.

Enclosed herewith for your information and forwarding to your clients for whose accounts you hold Shares registered in your name or in the name of your nominee are copies of the following documents:

YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE. PLEASE NOTE THAT THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, AT THE END OF DECEMBER 16, 2015, UNLESS THE OFFER IS EXTENDED.

The Offer is being made pursuant to the Agreement and Plan of Merger, dated as of November 5, 2015 (as amended from time to time, the “Merger Agreement”), among ZS Pharma, Parent and Purchaser. The Merger Agreement provides, among other things, that as soon as practicable after consummation of the Offer and subject to the satisfaction or waiver of the other conditions set forth in the Merger Agreement, Purchaser will merge with and into ZS Pharma (the “Merger”), with ZS Pharma continuing as the surviving corporation and a wholly owned subsidiary of Parent. At the effective time of the Merger, each outstanding Share (other than shares held by ZS Pharma, any of its subsidiaries, Parent, Purchaser or any other subsidiary of Parent, or any stockholders who have properly exercised their appraisal rights under Section 262 of the Delaware General Corporation Law (the “DGCL”)) will be converted into the right to receive the Offer Price in cash, without interest and less any required withholding taxes. No appraisal rights are available in connection with the Offer. However, pursuant to the DGCL, if the Merger is consummated, stockholders who do not tender their Shares in the Offer will have the right, by fully complying with the applicable provisions of Section 262 of the DGCL, to choose not to accept the consideration payable for their Shares pursuant to the Merger, and instead to demand an appraisal of their Shares by the Court of Chancery of the State of Delaware and receive a cash payment of the “fair value” of their Shares as of the effective time of the Merger as determined by the Court of Chancery of the State of Delaware. The “fair value” of such Shares as of the effective time of the Merger may be more than, less than, or equal to the Offer Price. The Merger Agreement is more fully described in Section 13 of the Offer to Purchase.

The Board of Directors of ZS Pharma (the “ZS Pharma Board”) has duly and unanimously (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Offer and the Merger, are fair to, and in the best interests of, ZS Pharma and its stockholders, (ii) approved and declared advisable the Merger Agreement and the transactions contemplated by the Merger Agreement, including the Offer and the Merger, (iii) resolved that the Merger Agreement shall be subject to Section 251(h) of the Delaware General Corporation Law (the “DGCL”) providing for consummation of the Merger without a meeting of the ZS Pharma stockholders, and (iv) recommended that the ZS Pharma stockholders tender all of their respective Shares into the Offer. ZS Pharma has been advised that all of its directors and executive officers intend to tender all of their transferrable Shares pursuant to the Offer.

The Offer is conditioned upon, among other things, (i) there being validly tendered in accordance with the terms of the Offer and not validly withdrawn, prior to the expiration of the Offer, a number of Shares (excluding Shares tendered pursuant to notices of guaranteed delivery for which Shares have not been delivered) that, when added to the Shares then owned by the Parent and its subsidiaries, would represent one share more than one half of all the Shares outstanding as of the closing of the Offer and (ii) the expiration or termination of any waiting period (and any extension thereof) under the Hart-Scott-Rodino Antitrust Improvement Act of 1976, as amended, except for an expiration or termination subject to the imposition of any action that would reasonably be expected to have a material and adverse effect on Parent and its controlled affiliates, considered as a whole. These and other conditions to the Offer are described in Sections 15 and 16 of the Offer to Purchase. There is no financing condition to the Offer.

Purchaser will not pay any fees or commissions to any broker, dealer or other person (other than to Mackenzie Partners, Inc. (the “Information Agent”) and the Depositary as described in the Offer to Purchase) for soliciting tenders of Shares pursuant to the Offer. Purchaser will, however, upon request, reimburse brokers, dealers, commercial banks, trust companies and other nominees for reasonable and necessary costs and expenses incurred by them in forwarding the enclosed materials to their customers.

Purchaser will pay all stock transfer taxes applicable to its purchase of Shares pursuant to the Offer, subject to Instruction 6 of the Letter of Transmittal.

In order to take advantage of the Offer, a duly executed and properly completed Letter of Transmittal (or a manually signed facsimile thereof), or an Agent’s Message (as defined in the Offer to Purchase) in connection with a book-entry

transfer of Shares, and any other required documents, should be sent to the Depositary, and certificates representing the tendered Shares should be delivered or such Shares should be tendered by book-entry transfer, all in accordance with the instructions contained in the Letter of Transmittal and in the Offer to Purchase.

If holders of Shares wish to tender, but it is impracticable for them to forward their certificates or other required documents or to complete the procedures for delivery by book-entry transfer prior to the expiration of the Offer, a tender may be effected by following the guaranteed delivery procedures described in Section 3 of the Offer to Purchase.

Any inquiries you may have with respect to the Offer should be addressed to, and additional copies of the enclosed materials may be obtained from, the Information Agent or the undersigned at the addresses and telephone numbers set forth on the back cover of the Offer to Purchase.

NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL RENDER YOU THE AGENT OF PARENT, PURCHASER, THE INFORMATION AGENT OR THE DEPOSITARY, OR ANY AFFILIATE OF ANY OF THEM, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE DOCUMENTS ENCLOSED HEREWITH AND THE STATEMENTS CONTAINED THEREIN.