Exhibit 99.1

AMENDMENT No. 1, dated as of August 14, 2012, (the “Amendment”) to the Credit Agreement, dated as of October 20, 2010, among DAVITA INC., a Delaware corporation (the “Borrower”), the several banks and other financial institutions or entities from time to time parties to the Credit Agreement (the “Lenders”), JPMORGAN CHASE BANK, N.A., as Administrative Agent (the “Administrative Agent”) and Collateral Agent (the “Collateral Agent”), JPMORGAN CHASE BANK, N.A., as Issuing Lender and Swingline Lender, the other agents from time to time party thereto (as supplemented by the Increase Joinder Agreement, dated as of August 26, 2011, and as further amended, restated, modified and supplemented from time to time, the “Credit Agreement”); capitalized terms used and not otherwise defined herein shall have the meanings assigned to such terms in the Credit Agreement.

WHEREAS, the Borrower desires to amend the Credit Agreement on the terms set forth herein, including without limitation to provide for the issuance of the New Senior Notes (as defined herein), the net proceeds of which shall be placed into the Escrow Account (as defined herein) pending consummation of the 2012 Transactions (as defined herein);

NOW, THEREFORE, in consideration of the premises contained herein and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto, intending to be legally bound hereby, agree as follows:

Section 1. Amendments. The Credit Agreement is hereby amended as follows:

(a) The following defined terms shall be added to Section 1.1 of the Credit Agreement:

“2012 Refinancing” shall mean (i) the repayment of outstanding Debt under the Tranche A-2 Term Facility and (ii) the repayment of outstanding Debt of Healthcare Partners Holdings, LLC.

“2012 Transactions” shall mean collectively, (a) the Acquisition and other related transactions contemplated by the Acquisition Agreement, (b) the incurrence of new Term Loans under the Credit Agreement pursuant to an amendment thereto after the Amendment No. 1 Effective Date; (c) the 2012 Refinancing; (d) the issuance of the New Senior Notes; and (e) the payment of all fees and expenses owing in connection with the foregoing.

“Acquisition” shall mean the acquisition of Healthcare Partners Holdings, LLC pursuant to the Acquisition Agreement.

“Acquisition Agreement” shall mean the Agreement and Plan of Merger (together with all exhibits and schedules thereto, collectively, the “Acquisition Agreement”), dated as of May 20, 2012, among the Borrower, Seismic Acquisition LLC, a newly formed limited liability company (“Merger Sub”) and a wholly-owned subsidiary of the Borrower, and Healthcare Partners Holdings, LLC (“Healthcare Partners”).

“Additional Escrow Amount” shall mean an amount equal to (a) all interest that could accrue on the New Senior Notes from and including the date of issuance thereof to and including the Termination Date and (b) all fees and expenses that are incurred in connection with the issuance of the New Senior Notes and all fees, expenses or other amounts payable in connection with the New Senior Notes Redemption.

“Eligible Escrow Investments” shall mean (1) U.S. Government Obligations maturing no later than the Business Day preceding Termination Date and (2) securities representing an interest or interests in money market funds registered under the Investment Company Act of 1940 whose shares are registered under the Securities Act as investing exclusively in direct obligations of the United States

“Escrow Account” shall mean a deposit or securities account at a financial institution (such institution, the “Escrow Agent”) into which the Escrowed Funds are deposited.

“Escrow Agent” shall have the meaning given to such term in the definition of the term “Escrow Account.”

“Escrowed Funds” shall mean an amount, in cash or Eligible Escrow Investments, not to exceed the sum of (a) the issue price of the New Senior Notes, plus (b) the Additional Escrow Amount, plus (c) so long as they are retained in the Escrow Account, any income, proceeds or products of the foregoing.

“New Senior Notes” shall mean debt securities issued after the Amendment No. 1 Effective Date of the Borrower to finance part of the 2012 Transactions (which may be guaranteed by one or more other Loan Parties, but may not be guaranteed or receive credit support from any Person other than another Loan Party); provided that the net proceeds of such debt securities are deposited into the Escrow Account upon the issuance thereof.

“New Senior Notes Escrow Documents” shall mean the agreement(s) governing the Escrow Account and any other documents entered into in order to provide the Escrow Agent (or its designee) a Lien on the Escrowed Funds.

“New Senior Notes Indenture” shall mean the indenture pursuant to which the New Senior Notes shall be issued.

“New Senior Notes Documents” shall mean the New Senior Notes Indenture, the New Senior Notes Escrow Documents and any other documents entered into by the Borrower in connection with the New Senior Notes; provided that such documents shall require that (a) if the 2012 Transactions shall not be

-2-

consummated on or before the Termination Date, the New Senior Notes shall be redeemed in full (the “New Senior Notes Redemption”) no later than the second Business Day after the Termination Date and (b) the Escrowed Funds shall be released from the Escrow Account before the Termination Date or within two Business Days after the Termination Date (A) upon the consummation of the 2012 Transactions and applied to finance part of the 2012 Transactions or (B) to effectuate the New Senior Notes Redemption.

“New Senior Notes Redemption” shall have the meaning given to such term in the definition of the term New Senior Notes Documents.

“Securities Act” shall mean the United States Securities Act of 1933, as amended, and the rules and regulations of the SEC promulgated thereunder.

“Termination Date” shall mean November 30, 2012; provided that the Borrower may elect to extend the Termination Date for an additional 30 days on no more than 3 occasions so long as (i) two Business days prior to the scheduled Termination Date it provides written notice to the Escrow Agent and the Administrative Agent and has issued a press release stating that it has extended the Termination Date, (ii) the Borrower has deposited cash or Eligible Escrow Investments into escrow with the Escrow Agent, to be held pursuant to the terms of the New Senior Notes Escrow Documents, in an amount sufficient to fund the redemption price due on the latest permitted date for the revised New Senior Notes Redemption in respect of all outstanding New Senior Notes and has certified that such amount will be satisfactory for such purpose and (iii) the Termination Date (as defined in the Acquisition Agreement) has been extended to match the extended Termination Date.

“U.S. Government Obligations” shall mean securities that are (a) direct obligations of the United States of America for the timely payment of which its full faith and credit is pledged or (b) obligations of a Person controlled or supervised by and acting as an agency or instrumentality of the United States of America the timely payment of which is unconditionally guaranteed as a full faith and credit obligation of the United States of America, which in either case, are not callable or redeemable at the option of the issuer thereof, and shall also include a depositary receipt issued by a bank (as defined in Section 3(a)(2) of the Securities Act), as custodian with respect to any such U.S. Government Obligations or a specific payment of principal of or interest on any such U.S. Government Obligations held by such custodian for the account of the holder of such depositary receipt; provided that (except as required by law) such custodian is not authorized to make any deduction from the amount payable to the holder of such depositary receipt from any amount received by the custodian in respect of the U.S. Government Obligations or the specific payment of principal of or interest on the U.S. Government Obligations evidenced by such depositary receipt.

-3-

(b) Section 1.1 of the Credit Agreement is hereby amended by adding the following proviso to the definition of “Collateral”:

“provided; that the Collateral shall not include the Escrowed Funds, the Escrow Account or any of the New Senior Notes Documents.”

(c) Section 1.1 of the Credit Agreement is hereby amended by adding the following proviso to the definition of “Security Documents”:

“provided; that the Security Documents shall not include the Escrow Account or any New Senior Notes Escrow Document.”

(d) A new Section 1.9 shall be added to the Credit Agreement as follows:

1.9 New Senior Notes. Notwithstanding anything to the contrary in any Loan Document, nothing contained in any Loan Document shall prevent (a) the incurrence of any Debt evidenced by any New Senior Note Document, (b) the granting or existence of any Liens on the Escrow Account, the Escrowed Funds or any New Senior Note Document or pursuant to any New Senior Notes Escrow Document, in each case, in favor of the Escrow Agent or the trustee under the New Senior Notes Indenture (or their designees), (c) the holding of the Escrowed Funds in the Escrow Account or (d) any other transaction contemplated by the New Senior Notes Documents (it being understood, for the avoidance of doubt, that any such incurrences of Debt, granting of Liens and other transactions shall be deemed made exclusively in reliance upon this Section 1.9 and not any other exception or basket under any other provision of any Loan Document). The Lenders, the Issuing Lenders and their respective Affiliates hereby agree that none of the Administrative Agent, the Collateral Agent or any Affiliate thereof shall have any liability or obligation to the Lenders, in their capacities as such, with respect to any transactions contemplated by the New Senior Notes Documents.

Section 2. Representations and Warranties, No Default. By its execution of this Agreement, each Loan Party hereby certifies that prior to and immediately after giving effect to this Agreement:

(a) the execution, delivery and performance by each Loan Party of this Agreement, are within such Loan Party’s corporate, partnership or limited liability company powers, as applicable, have been duly authorized by all necessary corporate, partnership or limited liability company action, as applicable, do not (i) contravene such Loan Party’s Constitutive Documents, (ii) violate any Requirements of Law, (iii) conflict with or result in the breach of, or constitute a default or require any payment to be made under, any material contract, loan agreement, indenture, mortgage, deed of trust, lease or other instrument binding on or affecting any Loan Party or any of its properties that

-4-

would reasonably be likely to have a Material Adverse Effect or (iv) except for the Liens created under the Loan Documents, result in or require the creation or imposition of any Lien upon or with respect to any of the properties of any Loan Party;

(b) no Default or Event of Default exists, or will result from the execution of this Agreement and the transactions contemplated hereby;

(c) each of the representations and warranties made by any Loan Party set forth in Section 4 of the Credit Agreement or in any other Loan Document shall be true and correct in all material respects (except that any representation and warranty that is qualified as to “materiality” or “Material Adverse Effect” shall be true and correct in all respects) on and as of the Amendment No.1 Effective Date with the same effect as though made on and as of such date, except to the extent such representations and warranties expressly relate to an earlier date.

Section 3. Effectiveness.

(a) The Amendment shall become effective on the date (such date, if any, the “Amendment No. 1 Effective Date”) that the following conditions have been satisfied:

(i) The Administrative Agent shall have received executed signature pages hereto from Lenders constituting the Required Lenders and each Loan Party; and

(ii) The representations and warranties in Section 2 hereof shall be true and correct.

Section 4. Counterparts. This Amendment may be executed in any number of counterparts and by different parties hereto on separate counterparts, each of which when so executed and delivered shall be deemed to be an original, but all of which when taken together shall constitute a single instrument. Delivery of an executed counterpart of a signature page of this Amendment by facsimile or any other electronic transmission shall be effective as delivery of a manually executed counterpart hereof.

Section 5. Governing Law and Waiver of Right to Trial by Jury.

(a) THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES UNDER THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK (INCLUDING, WITHOUT LIMITATION, SECTIONS 5-1401 AND 5-1402 OF THE NEW YORK GENERAL OBLIGATIONS LAW, BUT OTHERWISE WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES THEREOF). The jurisdiction and waiver of right to trial by jury provisions in Section 11.12 of the Credit Agreement are incorporated herein by reference mutatis mutandis.

-5-

Section 6. Headings. The headings of this Amendment are for purposes of reference only and shall not limit or otherwise affect the meaning hereof.

Section 7. Effect of Amendment. Except as expressly set forth herein, this Amendment (i) shall not by implication or otherwise limit, impair, constitute a waiver of or otherwise affect the rights and remedies of the Lenders, the Administrative Agent, any other Agent or the Issuing Lenders, in each case under the Credit Agreement or any other Loan Document, and (ii) shall not alter, modify, amend or in any way affect any of the terms, conditions, obligations, covenants or agreements contained in the Credit Agreement or any other provision of either such agreement or any other Loan Document. Each and every term, condition, obligation, covenant and agreement contained in the Credit Agreement or any other Loan Document is hereby ratified and re-affirmed in all respects and shall continue in full force and effect. Each Loan Party hereby expressly acknowledges the terms of this Amendment and reaffirms, as of the date hereof, (i) the covenants and agreements contained in each Loan Document to which it is a party, including, in each case, such covenants and agreements as in effect immediately after giving effect to this Amendment and the transactions contemplated hereby and (ii) its guarantee of the Obligations under the Guaranty, as applicable, and its grant of Liens on the Collateral to secure the Obligations pursuant to the Security Documents. This Amendment shall constitute a Loan Document for purposes of the Credit Agreement and from and after the Amendment No. 1 Effective Date, all references to the Credit Agreement in any Loan Document and all references in the Credit Agreement to “this Agreement,” “hereunder”, “hereof” or words of like import referring to the Credit Agreement, shall, unless expressly provided otherwise, refer to the Credit Agreement as amended by this Amendment. Each of the Loan Parties hereby consents to this Amendment and confirms that all obligations of such Loan Party under the Loan Documents to which such Loan Party is a party shall continue to apply to the Credit Agreement as amended hereby.

-6-

IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed by their respective authorized officers as of the day and year first above written.

 ITS MANAGER