AMENDMENT NO. 4 TO CREDIT AND SECURITY AGREEMENT

Exhibit 10.44

AMENDMENT NO. 4
TO
CREDIT AND SECURITY AGREEMENT

     THIS AMENDMENT NO. 4 to Credit and Security Agreement (this “ Amendment ”) is entered into this [ • ]th day of March, 2009 (the “ Fourth Amendment Date ”), by and among (a) NXSTAGE MEDICAL, INC. , a Delaware corporation, EIR MEDICAL, INC ., a Massachusetts corporation, MEDISYSTEMS SERVICES CORPORATION , a Nevada corporation, and MEDISYSTEMS CORPORATION , a Washington corporation, and any additional Borrower that may hereafter be added to the Credit Agreement (as defined below) (each individually as a “Borrower” and collectively as “Borrowers”), (b) GE BUSINESS FINANCIAL SERVICES INC. (formerly known as Merrill Lynch Business Financial Services Inc.) , individually as a Lender, and as Administrative Agent, and (c) the financial institutions or other entities signatory hereto as Lenders.

Recitals

      A.  Borrowers, Administrative Agent and the Lenders have entered into that certain Credit and Security Agreement dated as of November 21, 2007 as amended by Amendment No. 1 to Credit and Security Agreement dated as of June 27, 2008, Amendment No. 2 to Credit and Security Agreement dated as of June 30, 2008 and Amendment No. 3 to Credit and Security Agreement dated as of October 14, 2008 (as the same may from time to time be further amended, modified, supplemented or restated, the “ Credit Agreement ”).

      B.  The Lenders have extended credit to Borrowers for the purposes permitted in the Credit Agreement.

      C.  Borrowers have requested that Administrative Agent and the Lenders amend the Credit Agreement as more fully set forth herein.

      D.  Administrative Agent and the Lenders have agreed to so amend certain provisions of the Credit Agreement, but only to the extent, in accordance with the terms, subject to the conditions and in reliance upon the representations and warranties set forth below.

Agreement

      Now, Therefore, in consideration of the foregoing recitals and other good and valuable consideration, the receipt and adequacy of which is hereby acknowledged, and intending to be legally bound, the parties hereto agree as follows:

      1. Definitions. Capitalized terms used but not defined in this Amendment shall have the meanings given to them in the Credit Agreement.

      2. Amendments to Credit Agreement.

           2.1 Section 1.1 (Certain Defined Terms) . Section 1.1 of the Credit Agreement is hereby amended as follows:

                (a)  The following definitions in Section 1.1 of the Credit Agreement are hereby amended in their entirety and replaced with the following:

          ““ Base Rate ” means (a) the LIBOR Rate with respect to the Revolving Loans and other Obligations (other than the Term Loan) and (b) eleven and twelve one hundredths percent (11.12%) per annum with respect to the Term Loan.

          “ Base Rate Margin ” means (a) six and one half percent (6.50%) per annum with respect to the Revolving Loans and other Obligations (other than the Term Loan), and (b) no additional amount with respect to the Term Loan.

          “ LIBOR Rate ” means a rate per annum (rounded upwards, if necessary, to the nearest 1/100 of 1%) equal to the greater of (a) four percent (4.0%) per annum or (b)(i) the rate of interest which is identified and normally published by Bloomberg Professional Service Page BBAM 1 as the offered rate for loans in United States dollars for the period of three (3) months under the caption British Bankers Association LIBOR Rates as of 11:00 a.m. (London time) as adjusted on a daily basis and effective on the second full Business Day after each such day (unless such date is not a Business Day, in which event the next succeeding Business Day will be used); divided by (ii) the sum of one minus the daily average during the preceding month of the aggregate maximum reserve requirement (expressed as a decimal) then imposed under Regulation D of the Board of Governors of the Federal Reserve System (or any successor thereto) for “Eurocurrency Liabilities” (as defined therein). If Bloomberg Professional Service (or another nationally-recognized rate reporting source acceptable to Administrative Agent) no longer reports the LIBOR or Administrative Agent determines in good faith that the rate so reported no longer accurately reflects the rate available to Administrative Agent in the London Interbank Market or if such index no longer exists or if Page BBAM 1 no longer exists or accurately reflects the rate available to Administrative Agent in the London Interbank Market, Administrative Agent may select a comparable replacement index or replacement page, as the case may be, that has been accepted as comparable by the London Interbank Market.”

                (b)  The following definitions in Section 1.1 of the Credit Agreement are hereby amended as follows:

                     (i)  Clause (h) of “ Permitted Indebtedness ” is hereby amended in its entirety and replaced with “(h) Reserved;”

                     (ii)  Clause (j) of “ Permitted Liens ” is hereby amended in its entirety and replaced with “(j) Reserved.”

           2.2 Section 4.9 (Intellectual Property.) . The last sentence of Section 4.9 of the Credit Agreement is hereby amended in its entirety and replaced with the following:

          “Notwithstanding the foregoing, Borrowers shall be required to update Schedule 4.9 within 30 days of the end of each fiscal quarter of Borrowers beginning with the second fiscal quarter of 2009; provided , that , each Credit Party shall provide Administrative Agent with written notice at least three (3) Business Days in advance of any new registration by such Credit Party of its Intellectual Property with any Governmental Authority; provided ,

further , that it is understood that no Default or Event of Default will result if a Borrower shall fail to include each item of registered Intellectual Property if such Borrower is exercising commercially reasonable diligence when complying with such disclosures.”

           2.3 Section 5.4 ( Consolidations, Mergers and Sales of Assets; Change in Control. ). Section 5.4 of the Credit Agreement is hereby amended in its entirety and replaced with the following:

          “ Section 5.4 Consolidations, Mergers and Sales of Assets; Change in Control. No Borrower will, or will permit any Subsidiary to, directly or indirectly (a) consolidate or merge or amalgamate with or into any other Person, other than pursuant to a Permitted Acquisition, or (b) consummate any Asset Dispositions other than Permitted Asset Dispositions; provided , however , in no event shall a Borrower permit any Asset Disposition, including, without limitation, the transfer of any Intellectual Property, to any Subsidiary that is not a Credit Party. No Borrower will suffer or permit to occur any Change in Control with respect to itself, any Subsidiary or any guarantor of the Obligations.”

           2.4 Section 5.9 (Deposit Accounts and Securities Accounts.) . The first two sentences of Section 5.9 of the Credit Agreement are hereby amended in their entirety and replaced with the following:

          “ Section 5.9 Deposit Accounts and Securities Accounts. No Borrower will, or will permit any Subsidiary to, directly or indirectly, establish any new Deposit Account or Securities Account without prior written notice to Administrative Agent and unless Administrative Agent, such Borrower or such Subsidiary and the bank, financial institution or securities intermediary at which the account is to be opened enter into a Deposit Account Control Agreement or Securities Account Control Agreement prior to or concurrently with the establishment of such Deposit Account or Securities Account; provided , however , Subsidiaries that are not Credit Parties shall be permitted to maintain no more than $1,000,000 in the aggregate, of cash, Investment Property, Securities or other assets in Deposit Accounts or Securities Accounts in which Administrative Agent does not have a perfected security interest. Borrowers represent and warrant that Schedule 5.9 lists all of the Deposit Accounts and Securities Accounts of each Borrower as of the Fourth Amendment Date.”

           2.5 Section 6.1 (Additional Defined Terms) . The following definitions are inserted into Section 6.1 of the Credit Agreement in alphabetical order:

          ““ Adjusted Consolidated EBITDA ” means, for any period of four consecutive fiscal quarters, Borrowers’ Net Revenue less (a) cost of goods sold expense for such period, (b) research and development expense for such period, (c) selling and marketing expense for such period, (d) distribution expense for such period, (e) general and administrative expense for such period and (f) amortization of DaVita Deferred Revenue for such period plus to the extent included in the above expenses (x) asset and equipment depreciation for such period, (y) intangibles amortization for such period and (z) non-cash stock option expense for such period, all consistently reported in accordance with GAAP and Borrowers’ three year plan dated January 6, 2009.

          “ Cash Equivalents ” means (a) any readily-marketable securities (i) issued by, or directly, unconditionally and fully guaranteed or insured by the United States federal government or (ii) issued by any agency of the United States federal government the obligations of which are fully backed by the full faith and credit of the United States federal government, (b) any readily-marketable direct obligations issued by any other agency of the United States federal government, any state of the United States or any political subdivision of any such state or any public instrumentality thereof, in each case having a rating of at least “A-1” from S&P or at least “P-1” from Moody’s, (c) any commercial paper rated at least “A-1” by S&P or “P-1” by Moody’s and issued by any entity organized under the laws of any state of the United States, (d) any U.S. dollar-denominated time deposit, insured certificate of deposit, overnight bank deposit or bankers’ acceptance issued or accepted by (i) Administrative Agent or (ii) any commercial bank that is (A) organized under the laws of the United States, any state thereof or the District of Columbia, (B) “adequately capitalized” (as defined in the regulations of its primary federal banking regulators) and (C) has Tier 1 capital (as defined in such regulations) in excess of $250,000,000 or (e) shares of any United States money market fund that (i) has substantially all of its assets invested continuously in the types of investments referred to in clause (a), (b), (c) or (d) above with maturities as set forth in the proviso below, (ii) has net assets in excess of $500,000,000 and (iii) has obtained from either S&P or Moody’s the highest rating obtainable for money market funds in the United States; provided, however, that the maturities of all obligations specified in any of clauses (a), (b), (c) and (d) above shall not exceed 365 days. For the avoidance of doubt, “Cash Equivalents” does not include (and each Loan Party is prohibited from purchasing or purchasing participations in) any auction rate securities or other corporate or municipal bonds with a long-term nominal maturity for which the interest rate is reset through a Dutch auction.

          “ DaVita Deferred Revenue ” means such amounts recorded in the Borrowers’ financial statements consistently reported in accordance with GAAP and consistent with Borrowers’ three year plan dated as of January 6, 2009.

          “ Minimum Liquidity ” means the sum of Revolving Loan Availability plus (i) unrestricted cash, (ii) cash that is reserved solely for Borrowers’ compliance with Section 6.6 hereof and which shall not be used for any other purposes and (iii) Cash Equivalents which are (a) owned by a Borrower, (b) subject to a Deposit Account Control Agreement and/or a Securities Account Control Agreement, (c) not pledged to or held by Administrative Agent to secure a specified Obligation, and (d) not pledged to or held by Administrative Agent as an escrow or reserve required under this Agreement.”

           2.6 Section 6.2 ( Minimum Net Revenues. ). Section 6.2 of the Credit Agreement is hereby amended in its entirety and replaced with the following:

          “ Section 6.2 Minimum Net Revenues. Borrowers agree that an Event of Default shall be deemed to have occurred under this Agreement if the Borrowers’ Net Revenues for any twelve month trailing period preceding the end of each calendar quarter below (which shall be the Defined Period) shall be less than the amounts set forth below:

           2.7 Section 6.4 ( Evidence of Compliance. ).