<PAGE>
                                                                     EXHIBIT 4.8


                                 AMENDMENT NO. 1
                             TO AMENDED AND RESTATED
                  RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT


         THIS AMENDMENT NO. 1 TO AMENDED AND RESTATED RIGHT OF FIRST REFUSAL AND
CO-SALE AGREEMENT ("Amendment") is made and entered into as of August 11, 1999,
by and among SYMBION, INC., a Tennessee corporation formerly named "UniPhy
Healthcare, Inc." (the "Company"), and those Persons identified on Exhibit A
attached hereto (collectively, the "Investors" and each individually an
"Investor").

                                R E C I T A L S:

         WHEREAS, the Company and the Investors are parties to that certain
Amended and Restated Right of First Refusal and Co-Sale Agreement, dated as of
June 25, 1999 (the "Right of First Refusal and Co-Sale Agreement");

         WHEREAS, the Company and certain of the Investors are parties to that
certain Securities Purchase Agreement, dated as of July 6, 1999 (the "Purchase
Agreement");

         WHEREAS, Section 1(B) of the Purchase Agreement grants an option (the
"Option") of limited duration to Richland Ventures III, L.P. ("RVIII") to
purchase up to 3,191,489 shares (the "Option Shares") of the common stock, no
par value (the "Common Stock"), of the Company, at a purchase price of $1.88 per
share;

         WHEREAS, in the event that RVIII purchases the Option Shares, the
Company and the Investors desire that RVIII obtain the rights and obligations of
an "Investor" and an "ARC Key Shareholder" under the Right of First Refusal and
Co-Sale Agreement;

         WHEREAS, the Company may, pursuant to Section 1(C) of the Purchase
Agreement, issue and sell up to 5,319,149 shares (the "Reserve Shares") of
Common Stock (including the Option Shares) to any person or entity (each, a
"Reserve Share Purchaser");

         WHEREAS, in the event that a Reserve Share Purchaser purchases Reserve
Shares, the Company and the Investors may desire that such Reserve Share
Purchaser have the rights and obligations of an "Investor," a "UniPhy Preferred
Shareholder," a "UniPhy Founder" or an "ARC Key Shareholder" under the Right of
First Refusal and Co-Sale Agreement;

         WHEREAS, the Company and the Investors desire to amend the Right of
First Refusal and Co-Sale Agreement as set forth in this Amendment, pursuant to
Section 6(c) of the Right of First Refusal and Co-Sale Agreement; and

         WHEREAS, capitalized terms used herein without definition shall have
the same meanings ascribed to such terms in the Right of First Refusal and
Co-Sale Agreement.

         NOW, THEREFORE, in consideration of the foregoing and the respective
covenants and agreements contained herein, the sufficiency of which is hereby
acknowledged, the parties hereby agree and consent to the following:


<PAGE>


                               A G R E E M E N T:

1.       RVIII Amendment. The Right of First Refusal and Co-Sale Agreement is
hereby amended by adding and appending the following as Section 7 of the Right
of First Refusal and Co-Sale Agreement:

         7.       Addition of RVIII as a Party. Notwithstanding the provisions
         of Section 6(c) or any other Section hereof, upon the occurrence of:
         (i) the exercise by Richland Ventures III, L.P. ("RVIII") of the option
         (the "Option") to purchase up to 3,191,489 shares (the "Option Shares")
         of Common Stock at a purchase price of $1.88 per share which was
         granted to RVIII in Section 1(B) of that certain Securities Purchase
         Agreement, dated as of July 6, 1999 (the "Purchase Agreement"), among
         the Company and certain purchasers identified in such agreement, and
         the purchase of Option Shares by RVIII, and (ii) the execution and
         delivery to the Company by RVIII of a counterpart of this Amended and
         Restated Right of First Refusal and Co-Sale Agreement (as then
         amended), adopting and accepting the terms hereof, and (iii) acceptance
         and countersignature of such counterpart by the Company:

                  (a)      RVIII shall be a party to this Amended and Restated
         Right of First Refusal and Co-Sale Agreement; and

                  (b)      Exhibit A attached to this Amended and Restated Right
         of First Refusal and Co-Sale Agreement shall be amended to add RVIII as
         a person identified thereon, and RVIII shall be, and shall be included
         within the definition of, an "Investor" for purposes of this Amended
         and Restated Right of First Refusal and Co-Sale Agreement; and

                  (c)      RVIII shall be, and shall be included within the
          definition of, an "ARC Key Shareholder," for purposes of this Amended
          and Restated Right of First Refusal and Co-Sale Agreement; and

                  (d)      RVIII shall have, and be entitled and subject to, all
         of the rights, benefits, duties and obligations of an "Investor" and an
         "ARC Key Shareholder" under this Amended and Restated Right of First
         Refusal and Co-Sale Agreement, subject to the terms hereof.

2.       Reserve Share Purchasers Amendment. The Investors' Rights Agreement is
hereby further amended by adding and appending the following as Section 8
of the Investors' Rights Agreement:

         8.       Addition of Reserve Share Purchasers as Parties.

                  (a)      Reserve Share Purchasers. The parties hereto
         acknowledge and agree that, pursuant to Section 1(C) of the Purchase
         Agreement, the Company may issue, offer and sell up to 5,319,149 shares
         (the "Reserve Shares") of Common Stock (including the 3,191,489 Option
         Shares) to any person or entity (each, a "Reserve Share Purchaser").
         Notwithstanding the provisions of Section 6(c) or any other Section
         hereof, upon the occurrence of: (1) the purchase from the Company by a



                                       2
<PAGE>

         Reserve Share Purchaser of Reserve Shares (but not including the
         purchase of Option Shares by RVIII, which is addressed in and governed
         by Section 7 above), and (2) the execution and delivery to the Company
         by such Reserve Share Purchaser of a counterpart of this Amended and
         Restated Right of First Refusal and Co-Sale Agreement (as then
         amended), adopting and accepting the terms hereof, and (3) acceptance
         and countersignature of such counterpart by the Company:

                           (i)      such Reserve Share Purchaser shall be a
         party to this Amended and Restated Right of First Refusal and Co-Sale
         Agreement; and

                           (ii)     Exhibit A attached to this Amended and
         Restated Right of First Refusal and Co-Sale Agreement shall be amended
         to add such Reserve Share Purchaser as a person identified thereon, and
         such Reserve Share Purchaser shall be, and shall be included within the
         definition of, an "Investor" for purposes of this Amended and Restated
         Right of First Refusal and Co-Sale Agreement; and

                           (iii)    subject to Section 8(b) below, such Reserve
         Share Purchaser shall be, and shall be included within the definition
         of, either of a "UniPhy Preferred Shareholder," a "UniPhy Founder" or
         an "ARC Key Shareholder" (as designated by the Company pursuant to
         Section 8(b) below), for purposes of this Amended and Restated Right of
         First Refusal and Co-Sale Agreement; and

                           (iv)     subject to Section 8(b) below, such Reserve
         Share Purchaser shall have, and shall be entitled and subject to, all
         of the rights, benefits, duties and obligations of an "Investor" and a
         "UniPhy Preferred Shareholder," a "UniPhy Founder" or an "ARC Key
         Shareholder" (as designated by the Company pursuant to Section 8(b)
         below) under this Amended and Restated Right of First Refusal and
         Co-Sale Agreement, subject to the terms hereof.

                  (b)      Designation as UniPhy Preferred Shareholder, UniPhy
         Founder or ARC Key Shareholder. The Company shall have the right, power
         and authority, to determine, in its discretion, in negotiation or
         agreement with one or more Reserve Share Purchasers or otherwise,
         whether or not a particular Reserve Share Purchaser shall (in addition
         to becoming a party hereto and an "Investor" hereunder) be identified
         and/or designated as a "UniPhy Preferred Shareholder," a "UniPhy
         Founder" or an "ARC Key Shareholder" for purposes of this Amended and
         Restated Right of First Refusal and Co-Sale Agreement, and thereby
         have, and be entitled and subject to, all of the rights, benefits,
         duties and obligations of such designation or identification under this
         Amended and Restated Right of First Refusal and Co-Sale Agreement,
         pursuant to Sub-sections 8(a)(iii) and (iv) above.

3.       Requisite Approval. Upon execution and delivery of this Amendment by
         the Company and Investors representing the requisite percentage of the
         shares of Common Stock set forth in Section 6(c) of the Right of First
         Refusal and Co-Sale Agreement, this Amendment shall constitute and be
         deemed to be an amendment to and part of the Right of First Refusal and
         Co-Sale Agreement.


                                       3
<PAGE>


4.       No Other Changes. Except as expressly set forth or contemplated in this
Amendment, the terms and conditions of the Right of First Refusal and Co-Sale
Agreement shall remain in place and shall not be altered, amended or changed in
any manner whatsoever, except by any further amendment to the Right of First
Refusal and Co-Sale Agreement made in accordance with the terms of the Right of
First Refusal and Co-Sale Agreement, as hereby amended.

5.       Counterparts. This Amendment may be executed in any number of
counterparts and by the different parties hereto on separate counterparts, each
of which when executed and delivered shall be deemed an original effective for
binding the parties hereto, but all of which shall together constitute one and
the same instrument.


                                       4
<PAGE>


         IN WITNESS WHEREOF, the parties hereto have executed this Amendment to
Amended and Restated Right of First Refusal and Co-Sale Agreement, and hereby
consent to the amendment and modification of the Right of First Refusal and
Co-Sale Agreement provided herein, as of the date first above written.


THE COMPANY:

SYMBION, INC.


By: /s/ Richard E. Francis, Jr.
   -----------------------------------------
Name: Richard E. Francis, Jr.
Title: President and Chief Executive Officer



INVESTORS:


UNIPHY PREFERRED SHAREHOLDERS:


ABS CAPITAL PARTNERS, L.P.


/s/ ABS Partners, L.P.
--------------------------------------------
By: /s/ Frederick L. Bryant
    ----------------------------------------
Name: Frederick L. Bryant
      --------------------------------------
Title:   General Partner
       -------------------------------------


/s/ Clifford G. Adlerz
--------------------------------------------
Clifford G. Adlerz


/s/ Randy W. Cook
--------------------------------------------
Randy W. Cook


/s/ Paul Davis
--------------------------------------------
Paul Davis


/s/ Richard E. Francis, Jr.
-----------------------------------------------------
Richard E. Francis, Jr.


/s/ R. Dale Kennedy
--------------------------------------------
R. Dale Kennedy


                                       5
<PAGE>

--------------------------------------------
Tod Lambert


MARTIN INVESTMENT PARTNERSHIP II


/s/ Charles N. Martin, Jr.
-------------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------


/s/ Kenneth C. Mitchell
-------------------------------------------
Kenneth C. Mitchell


PACIFIC VENTURE GROUP, L.P.
By:      PVG Equity Partner, L.L.C.,
         its General Partner

/s/ Eve M. Kurtin
-------------------------------------------
By: Eve M. Kurtin
Title: Member


PVG ASSOCIATES, L.P.
By:      PVG Equity Partner, L.L.C.,
         its General Partner

/s/ Eve M. Kurtin
-------------------------------------------
By: Eve M. Kurtin
Title: Member


/s/ Patrick R. Rooney
-------------------------------------------
Patrick R. Rooney


/s/ Teresa F. Sparks
-------------------------------------------
Teresa F. Sparks


/s/ Gregg Stanley
-------------------------------------------
Gregg Stanley


/s/ Anthony Taparo
-------------------------------------------
Anthony Taparo




                                       6
<PAGE>

ARC KEY SHAREHOLDERS:


ARTHUR S. DEMOSS FOUNDATION


By:
    ---------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------


/s/ Jerry M. Eyler
-------------------------------------------
Jerry M. Eyler


FIRST AVENUE PARTNERS, L.P.

/s/ Front Street, LLC, General Partner
--------------------------------------
Name: David M. Wilds
     --------------------------------------
Title: Managing Member
       ------------------------------------


-------------------------------------------
William H. Freeman


-------------------------------------------
J. Michael Gould


HEALTH TECH AFFILIATES, INC.


By:
    ---------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------


HLM/CB FUND, L.P.

-------------------------------------------
By:
    ---------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------



                                       7
<PAGE>

HLM PARTNERS VII, L.P.


-------------------------------------------
By:
    ---------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------


-------------------------------------------
W. Lawrence Hough


PIPER JAFFRAY, INC.

By:
    ---------------------------------------
Name:
     --------------------------------------
Title:
       ------------------------------------


-------------------------------------------
B. Max Lauderdale


/s/ Charles N. Martin, Jr.
-------------------------------------------
Charles N. Martin, Jr.


/s/ Charles T. Neal
-------------------------------------------
Charles T. Neal


-------------------------------------------
Richard Panek


-------------------------------------------
Thomas Patten


-------------------------------------------
Keith B. Pitts


-------------------------------------------
Gary J. Prosterman



                                       8
<PAGE>


RICHLAND VENTURES II, L.P.


By: /s/ Jack Tyrrell
    ---------------------------------------
Name: Jack Tyrrell
     --------------------------------------
Title: Partner
       ------------------------------------


-------------------------------------------
Ann R. Schaaf


SOUTH ATLANTIC PRIVATE EQUITY FUND IV (QP), LIMITED PARTNERSHIP
         By: South Atlantic Private Equity Partners IV, Limited Partnership,
             its general partner

             By:  /s/ Donald W. Burton
                  ---------------------------------------
             Name: Donald W. Burton
                   --------------------------------------
             Title: Chairman
                    -------------------------------------



South Atlantic Private Equity Fund IV, L.P.
         By: South Atlantic Private Equity Partners IV, Limited Partnership,
             its general partner

             By:  /s/ Donald W. Burton
                  ---------------------------------------
             Name: Donald W. Burton
                   --------------------------------------
             Title: Chairman
                    -------------------------------------


---------------------------------------------------------
Cal Turner, Jr.


/s/ William V.B. Webb
---------------------------------------------------------
William V.B. Webb


WW TWO, L.P.

---------------------------------------------------------
By:
    -----------------------------------------------------
Name:
     ----------------------------------------------------
Title:
       --------------------------------------------------



                                       9
<PAGE>

-----------------------------------------------------
James A. Webb, III



UNIPHY FOUNDERS:



-----------------------------------------------------
Peter Davidson


-----------------------------------------------------
Shannon W. Fiser


THE FRANCIS IRREVOCABLE TRUST, ANN FRANCIS, TRUSTEE

/s/ Richard E. Francis, Jr.
-----------------------------------------------------
Name: Richard E. Francis, Jr.
      -----------------------------------------------
Title:
       ----------------------------------------------


-----------------------------------------------------
Victor Giovanetti


/s/ George M. Goodwin
-----------------------------------------------------
George M. Goodwin


-----------------------------------------------------
Marlene D. Kelley


/s/ H. Edward Kleine III
-----------------------------------------------------
H. Edward Kleine III


-----------------------------------------------------
Darrell Naish


-----------------------------------------------------
Richard Panek


/s/ Vickie R. Warren
-----------------------------------------------------
Vickie R. Warren



                                       10
<PAGE>



                                    EXHIBIT A

                              SCHEDULE OF INVESTORS

UNIPHY PREFERRED SHAREHOLDERS

ABS Capital Partners, L.P.*
Clifford G. Adlerz*
Randy W. Cook*
Paul Davis*
Richard E. Francis, Jr.*
R. Dale Kennedy*
Tod Lambert
Martin Investment Partnership II*
Kenneth C. Mitchell*
Pacific Venture Group, L.P.*
PVG Associates, L.P.*
Patrick R. Rooney*
Teresa F. Sparks*
Gregg Stanley*
Anthony Taparo*


ARC KEY SHAREHOLDERS

Arthur S. Demoss Foundation*
Jerry M. Eyler*
First Avenue Partners, L.P.*
William H. Freeman
J. Michael Gould
Health Tech Affiliates, Inc.
HLM/CB Fund, L.P.*
HLM Partners VII, L.P.*
W. Lawrence Hough
Piper Jaffray, Inc.*
B. Max Lauderdale
Charles N. Martin, Jr.*
Charles T. Neal*
Thomas Patten
Keith B. Pitts
Gary J. Prosterman
Richland Ventures II, L.P.*
Ann R. Schaaf
South Atlantic Private Equity Fund IV (QP)*
South Atlantic Private Equity Fund IV, L.P.*
Cal Turner, Jr.*
William V.B. Webb*
WW Two, L.P.*
James A. Webb, III

*   ANTI-DILUTION INVESTOR




<PAGE>

UNIPHY FOUNDERS

Peter Davidson
Shannon W. Fiser
The Francis Irrevocable Trust, Ann Francis, Trustee*
Victor Giovanetti
George M. Goodwin
Marlene D. Kelley
H. Edward Kleine III
Darrell Naish
Richard Panek
Vickie R. Warren






*  ANTI-DILUTION INVESTOR



                                       2