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                               UNITED STATES
                     SECURITIES AND EXCHANGE COMMISSION
                           WASHINGTON, D.C. 20549


                                SCHEDULE 13G
                    (AMENDMENT NO. 1 - FINAL AMENDMENT)

                 UNDER THE SECURITIES EXCHANGE ACT OF 1934

                      United Therapeutics Corporation
------------------------------------------------------------------------------
                              (Name of Issuer)

           Common Stock, par value $.01 per share and associated
                      preferred stock purchase rights
------------------------------------------------------------------------------
                       (Title of Class of Securities)

                                 91307C102
                     ---------------------------------
                               (CUSIP Number)


                               December 31, 2005
                     ---------------------------------
          (Date of Event which Requires Filing of this Statement)



Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:

                      |_| Rule 13d-1(b)

                      |X| Rule 13d-1(c)

                      |_| Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which
would alter disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities
Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of
that section of the Act but shall be subject to all other provisions of the
Act (however, see the Notes).



----------------------                         -------------------------------
CUSIP NO.91307C102                13G                  PAGE 2 OF 9 PAGES
----------------------                         -------------------------------


------------------------------------------------------------------------------
   1    NAMES OF REPORTING PERSONS
        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
                       Ziff Asset Management, L.P.

------------------------------------------------------------------------------
   2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
        (SEE INSTRUCTIONS)                                             (A) |_|
                                                                       (B) |_|

------------------------------------------------------------------------------
   3    SEC USE ONLY

------------------------------------------------------------------------------
   4    CITIZENSHIP OR PLACE OF ORGANIZATION

                       Delaware

------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF                    0
       SHARES
                    ----------------------------------------------------------
                     6    SHARED VOTING POWER
    BENEFICIALLY
                                  930,455
      OWNED BY
                    ----------------------------------------------------------
        EACH         7    SOLE DISPOSITIVE POWER

                                  0
     REPORTING
                    ----------------------------------------------------------
       PERSON        8    SHARED DISPOSITIVE POWER
        WITH
                                  930,455

------------------------------------------------------------------------------
   9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                930,455

------------------------------------------------------------------------------
  10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
        (SEE INSTRUCTIONS)                                                 |_|

------------------------------------------------------------------------------
  11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

                4.0%

------------------------------------------------------------------------------
  12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

                PN

------------------------------------------------------------------------------



----------------------                         -------------------------------
CUSIP NO. 91307C102               13G                  PAGE 3 OF 9 PAGES
----------------------                         -------------------------------

------------------------------------------------------------------------------
   1    NAMES OF REPORTING PERSONS
        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
                       PBK Holdings, Inc.

------------------------------------------------------------------------------
   2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
        (SEE INSTRUCTIONS)                                             (A) |_|
                                                                       (B) |_|

------------------------------------------------------------------------------
   3    SEC USE ONLY

------------------------------------------------------------------------------
   4    CITIZENSHIP OR PLACE OF ORGANIZATION

                       Delaware

------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF                    0
       SHARES
                    ----------------------------------------------------------
                     6    SHARED VOTING POWER
    BENEFICIALLY
                                  930,455
      OWNED BY
                    ----------------------------------------------------------
        EACH         7    SOLE DISPOSITIVE POWER

                                  0
     REPORTING
                    ----------------------------------------------------------
       PERSON        8    SHARED DISPOSITIVE POWER
        WITH
                                  930,455

------------------------------------------------------------------------------
   9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                930,455

------------------------------------------------------------------------------
  10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
        (SEE INSTRUCTIONS)                                                 |_|

------------------------------------------------------------------------------
  11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

                4.0%

------------------------------------------------------------------------------
  12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

                CO

------------------------------------------------------------------------------



----------------------                         -------------------------------
CUSIP NO. 91307C102               13G                  PAGE 4 OF 9 PAGES
----------------------                         -------------------------------

------------------------------------------------------------------------------
   1    NAMES OF REPORTING PERSONS
        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
                       Philip B. Korsant

------------------------------------------------------------------------------
   2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
        (SEE INSTRUCTIONS)                                             (A) |_|
                                                                       (B) |_|

------------------------------------------------------------------------------
   3    SEC USE ONLY

------------------------------------------------------------------------------
   4    CITIZENSHIP OR PLACE OF ORGANIZATION

                       United States of America

------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF                    0
       SHARES
                    ----------------------------------------------------------
                     6    SHARED VOTING POWER
    BENEFICIALLY
                                  930,455
      OWNED BY
                    ----------------------------------------------------------
        EACH         7    SOLE DISPOSITIVE POWER

                                  0
     REPORTING
                    ----------------------------------------------------------
       PERSON        8    SHARED DISPOSITIVE POWER
        WITH
                                  930,455

------------------------------------------------------------------------------
   9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                930,455

------------------------------------------------------------------------------
  10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
        (SEE INSTRUCTIONS)                                                 |_|

------------------------------------------------------------------------------
  11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

                4.0%

------------------------------------------------------------------------------
  12    TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

                IN

------------------------------------------------------------------------------




ITEM 1. (a)    NAME OF ISSUER

United Therapeutics Corporation

ITEM 1. (b)    ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES

1110 Spring Street
Silver Spring, MD  20910

ITEM 2. (a)    NAME OF PERSON FILING

This Schedule 13G is being filed on behalf of the following persons (the
"Reporting Persons")*:

(i)     Ziff Asset Management, L.P. ("ZAM");
(ii)    PBK Holdings, Inc. ("PBK"); and
(iii)   Philip B. Korsant.

*       Attached as Exhibit A is a copy of an agreement among the Reporting
Persons that this Schedule 13G is being filed on behalf of each of them.

ITEM 2. (b)    ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE

Ziff Asset Management, L.P.
283 Greenwich Avenue
Greenwich, CT  06830

PBK Holdings, Inc.
283 Greenwich Avenue
Greenwich, CT  06830

Philip B. Korsant
283 Greenwich Avenue
Greenwich, CT  06830

ITEM 2. (c)    CITIZENSHIP

See Item 4 of the attached cover pages.

ITEM 2. (d)    TITLE OF CLASS OF SECURITIES

Common Stock, par value $.01 per share and associated preferred
stock purchase rights

ITEM 2. (e)    CUSIP NUMBER

91307C102

ITEM 3.

Not applicable as this Schedule 13G is filed pursuant to Rule 13d-1(c).

ITEM 4. OWNERSHIP

(a)     Amount beneficially owned:

        See Item 9 of the attached cover pages.

(b)     Percent of class:

        See Item 11 of the attached cover pages.

(c)     Number of shares as to which such person has:

        (i)    Sole power to vote or to direct the vote:

               See Item 5 of the attached cover pages.

        (ii)   Shared power to vote or to direct the vote:

               See Item 6 of the attached cover pages.

        (iii)  Sole power to dispose or to direct the disposition:

               See Item 7 of the attached cover pages.

        (iv)   Shared power to dispose or to direct the disposition:

               See Item 8 of the attached cover pages.

ITEM 5.        OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

Item 5 is hereby amended and restated in its entirety as follows:

If this statement is being filed to report the fact that as of the date
hereof the reporting person has ceased to be the beneficial owner of more
than five percent of the class of securities, check the following [X].

ITEM 6.        OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

Item 6 is hereby amended and restated in its entirety as follows:

Not Applicable.

ITEM 7.        IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH
               ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING
               COMPANY

Not Applicable.

ITEM 8.        IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

Not Applicable.

ITEM 9.        NOTICE OF DISSOLUTION OF GROUP

Not Applicable.

ITEM 10.       CERTIFICATION

By signing  below I certify  that,  to the best of my knowledge and belief,
the securities referred to above were not acquired and are not held for the
purpose of or with the effect of changing or influencing the control of the
issuer  of the  securities  and  were  not  acquired  and are  not  held in
connection with or as a participant in any transaction  having that purpose
or effect.



                                  SIGNATURE


     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true,  complete
and correct.

Dated:  February 13, 2006

                                    ZIFF ASSET MANAGEMENT, L.P.
                                    By:PBK Holdings, Inc., its general partner


                                    By:/s/ DAVID GRAY
                                       -----------------------------
                                       Name:  David Gray
                                       Title: Vice President


                                    PBK HOLDINGS, INC.


                                    By:/s/ DAVID GRAY
                                       ------------------------------
                                       Name:  David Gray
                                       Title: Vice President


                                        /s/ PHILIP B. KORSANT
                                       ------------------------------
                                            Philip B. Korsant






                                  EXHIBIT A


     The  undersigned,  Ziff Asset  Management,  L.P.,  a Delaware  limited
partnership,  PBK  Holdings,  Inc., a Delaware  corporation,  and Philip B.
Korsant hereby agree and acknowledge that the information  required by this
Schedule 13G, to which this  Agreement is attached as an exhibit,  is filed
on behalf of each of them. The  undersigned  further agree that any further
amendments or supplements  thereto shall also be filed on behalf of each of
them.

Dated:  February 13, 2006

                                    ZIFF ASSET MANAGEMENT, L.P.
                                    By:PBK Holdings, Inc., its general partner


                                    By:/s/ DAVID GRAY
                                       -----------------------------
                                       Name:  David Gray
                                       Title: Vice President


                                    PBK HOLDINGS, INC.


                                    By:/s/ DAVID GRAY
                                       ------------------------------
                                       Name:  David Gray
                                       Title: Vice President


                                        /s/ PHILIP B. KORSANT
                                       ------------------------------
                                            Philip B. Korsant