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                                                                  EXHIBIT 10.161


                       SIXTH AMENDMENT TO LOAN AGREEMENT


          THIS SIXTH AMENDMENT TO LOAN AGREEMENT (this "Amendment") is made as
of the 20th day of December, 2000, by and among PHARMACEUTICAL PRODUCT
DEVELOPMENT, INC., a North Carolina corporation (together with its successors,
the "Borrower"); PPD DEVELOPMENT, LLC, a Texas limited liability company,
formerly PPD DEVELOPMENT, INC., a Texas corporation formerly known as PPD
PHARMACO, INC., a Texas corporation (the "Guarantor"); and WACHOVIA BANK, N.A.,
a national banking association (together with its endorsees, successors and
assigns, the "Bank").

                               R E C I T A L S:
                               ---------------

          The Borrower, the Guarantor and the Bank are parties to a certain Loan
Agreement dated as of August 7, 1997, as amended pursuant to an Amendment to
Loan Agreement dated as of August 6, 1998, a Second Amendment to Loan Agreement
dated as of January 30, 1999, a Third Amendment to Loan Agreement dated as of
November 11, 1999, a Fourth Amendment to Loan Agreement dated as of February 23,
2000, and a Fifth Amendment to Loan Agreement dated as of August 1, 2000 (the
"Loan Agreement").

          Capitalized terms used in this Amendment which are not otherwise
defined in this Amendment shall have the respective meanings assigned to them in
the Loan Agreement.

          The Borrower has requested certain modifications to the Loan Agreement
and the Bank is willing to modify the Loan Agreement subject to the terms,
provisions and conditions set forth in this Amendment.

          NOW, THEREFORE, in consideration of the Recitals, the mutual promises
herein contained and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Borrower, the Guarantor and
the Bank, intending to be legally bound hereby, agree as follows:

          SECTION 1.  Recitals.  The Recitals are incorporated herein by
                      --------
reference and shall be deemed to be a part of this Amendment.

          SECTION 2.  Amendment.  Effective from and after December 20, 2000,
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the Loan Agreement is hereby amended as follows:

          2.1  In Section 6.9 of the Loan Agreement, subsection (d) is amended
to read as follows and subsections (h) and (i) are re-lettered as (k) and (l),
respectively, and new subsections (h), (i) and (j) are hereby added to Section
6.9 of the Loan Agreement to read as follows:
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          "(d) Investments in and to Axys Pharmaceuticals, Inc. and/or PPGx,
     Inc., in an aggregate principal amount (on a cost basis) not to exceed
     $3,500,000 at any time except as provided in subsections (i) and (j)
     below;"

          "(h) acquisition of capital stock of DNA Sciences, Inc. in an amount
     not to exceed $15,000,000;

          (i)  cash equity investment in PPGx, Inc. in an amount not to exceed
     $4,700,000 (which amount represents fifty percent (50%) of the outstanding
     amounts (principal and interest) due under the Loan Agreement dated as of
     February 1, 1999 among PPGx, Inc., the Borrower and First Union National
     Bank);

          (j)  acquisition of capital stock of PPGx, Inc. in an amount not to
     exceed $5,900,000;"

          SECTION 3.  Conditions to Effectiveness.  The effectiveness of this
                      ---------------------------
Amendment and the obligations of the Bank hereunder are subject to receipt by
the Bank of the following:

          (a)  an original Amendment, duly executed by the Borrower and the
     Guarantor;

          (b)  a certificate of incumbency satisfactory to the Bank, certifying
     as to the names, true signatures and incumbency of the officer or officers
     of the Borrower and the members or managers of the Guarantor authorized to
     execute and deliver this Amendment;

          (c)  such other documents or items as the Bank or its counsel may
     reasonably request.

The effectiveness of this Amendment and the obligations of the Bank hereunder
are further subject to the condition that no Event of Default or event or
condition which with notice or lapse of time, or both, would constitute an Event
of Default under the Loan Agreement, as hereby amended, shall have occurred and
be continuing, and the representations and warranties contained in Section 5 of
the Loan Agreement, as amended herein, are true on and as of the date hereof.

          SECTION 4.  No Other Amendment.  Except for the amendments set forth
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above, the Loan Agreement shall remain unchanged and in full force and effect.
This Amendment is not intended to effect, nor shall it be construed as, a
novation.  The Loan Agreement and this Amendment shall be construed together as
a single agreement.  Nothing herein contained shall waive, annul, alter, limit,
diminish, vary or affect any provision, condition, covenant or agreement
contained in the Loan Agreement, except as herein amended, nor affect or

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impair any rights, powers or remedies under the Loan Agreement as hereby
amended. The Bank does hereby reserve all of its rights and remedies against all
parties who may be or may hereafter become secondarily liable for the repayment
of the Loan. The Borrower and the Guarantor promise and agree to perform all of
the requirements, conditions, agreements and obligations under the terms of the
Loan Agreement, as hereby amended, the Loan Agreement, as amended, and the
Guaranty contained in the Loan Agreement, being hereby ratified and affirmed.
The Borrower and Guarantor hereby expressly agree that the Loan Agreement, as
amended, is in full force and effect and confirm that they have no set off,
counterclaim or defense with respect to the Loan Agreement, the Loan, the Note,
the Guaranty contained in the Loan Agreement or the Guaranteed Obligations.

          SECTION 5.  Representations and Warranties.  The Borrower and the
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Guarantor hereby represent and warrant to the Bank as follows:

          (a)  No Event of Default or event or condition which with notice or
     lapse or time, or both, would constitute an Event of Default under the Loan
     Agreement, as hereby amended, has occurred and is continuing on the date
     hereof.

          (b)  The representations and warranties contained in Section 5 of the
     Loan Agreement, as amended herein, are true on and as of the date of this
     Amendment.

          (c)  This Amendment has been duly authorized, validly executed and
     delivered by one or more authorized officers of the Borrower and the
     Guarantor, and constitutes the legal, valid and binding obligation of the
     Borrower and Guarantor enforceable against them in accordance with its
     terms.

          (d)  The execution and delivery of this Amendment and the Borrower's
     and the Guarantor's performance hereunder do not and will not require the
     consent or approval of any regulatory authority or governmental authority
     or agency having jurisdiction over the Borrower or the Guarantor, nor be in
     contravention of or in conflict with the Articles of Incorporation or
     Bylaws of the Borrower or the operating agreement or Articles of
     Organization of the Guarantor, or the provision of any statute, or any
     judgment, order or indenture, instrument, agreement or undertaking to which
     the Borrower or the Guarantor is party or by which the Borrower's or the
     Guarantor's assets or properties are or may become bound.

          SECTION 6.  Counterparts.  This Amendment may be executed in
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counterparts, each of which shall be deemed to be an original and all of which,
taken together, shall constitute one and the same agreement.

          SECTION 7.  Governing Law.  This Amendment shall be deemed to be made
                      -------------
pursuant to the laws of the State of North Carolina with respect to agreements
made and to be

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performed wholly in the State of North Carolina and shall be construed,
interpreted, performed and enforced in accordance therewith.

          SECTION 8.  Costs and Expenses.  The Borrower shall pay any and all
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out-of-pocket expenses in connection with the preparation, execution and
delivery of this Amendment, including, without limitation, the fees and expenses
of the Bank's counsel in connection therewith.

          SECTION 9.  Entire Agreement.  This Amendment contains the entire
                      ----------------
agreement of the parties with respect to the subject matter hereof, and there
are no representations, inducements or other provisions among the parties
regarding such subject matter other than those expressed herein in writing.  All
changes, additions or deletions to this Amendment must be in writing and signed
by all parties.

          IN WITNESS WHEREOF, the parties hereto have caused their respective
duly authorized officers or representatives to execute and deliver this
Amendment as of the day and year first above written.


                                        BORROWER:

ATTEST:                                 PHARMACEUTICAL PRODUCT
                                        DEVELOPMENT, INC.

/s/ Fred B. Davenport, Jr.              By: /s/Fredric N. Eshelman
---------------------------------           ----------------------
Fred B. Davenport, Jr.  Secretary       Title: Chief Executive Officer


[CORPORATE SEAL]


                                        BANK:

                                        WACHOVIA BANK, N.A.


                                        By: /s/ Alex K. Turner
                                            ------------------
                                        Title:  Assistant Vice President


                                        GUARANTOR:

                                        PPD DEVELOPMENT, LLC             (SEAL)


                                        By: /s/ Fredric N. Eshelman   (SEAL)
                                            -------------------------
                                                      Manager

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