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

                                   ----------

                                    FORM 8-K

                                 CURRENT REPORT
     PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

                Date of report (date of earliest event reported):
                                JANUARY 31, 2005

                            PROTEIN DESIGN LABS, INC.
             (Exact name of registrant as specified in its charter)

           Delaware                      000-19756               94-3023969
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(State or other jurisdiction of    (Commission File No.)     (I.R.S. Employer
        incorporation)                                      Identification No.)

                               34801 Campus Drive
                            Fremont, California 94555
                    (Address of principal executive offices)

               Registrant's telephone number, including area code:
                                 (510) 574-1400

Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any of the
following provisions (see General Instruction A.2. below):

[ ]  Written communications pursuant to Rule 425 under the Securities
     Act (17 CFR 230.425)

[ ]  Soliciting material pursuant to Rule 14a-12 under the Exchange
     Act (17 CFR 240.14a-12)

[ ]  Pre-commencement communications pursuant to Rule 14d-2(b) under the
     Exchange Act (17 CFR 240.14d-2(b))

[ ]  Pre-commencement communications pursuant to Rule 13e-4(c) under the
     Exchange Act (17 CFR 240.13e-4(c))

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ITEM 1.01 ENTRY INTO A MATERIAL DEFINITIVE AGREEMENT. On February 1, 2005, Protein Design Labs, Inc., a Delaware corporation ("PDL" or the "Company") announced that it has entered into an Amendment No. 1 to Agreement and Plan of Merger, dated as of January 31, 2005 (the "Amendment"), by and among Protein Design Labs, Inc., Big Dog Bio, Inc., a Delaware corporation and a wholly-owned subsidiary of PDL ("Merger Sub"), ESP Pharma Holding Company, Inc., a Delaware corporation ("ESP Pharma"), and certain other individuals and entities, amending that certain Agreement and Plan of Merger, dated as of January 24, 2005 (the "Merger Agreement"), by and among PDL, Merger Sub, ESP Pharma and certain other individuals and entities, pursuant to which Merger Sub will be merged with and into ESP Pharma (the "Merger"), with ESP Pharma surviving the merger as a wholly owned subsidiary of PDL. The press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference. The Amendment increases the purchase price under the Merger Agreement by $25 million in cash to $325 million in cash and approximately $175 million in shares of PDL Common Stock, or an aggregate purchase price of approximately $500 million. The parties amended the Merger Agreement following ESP Pharma's recent entering into an agreement with Centocor, a biopharmaceutical operating company of Johnson & Johnson to purchase certain product rights and assets relating to a product known as Retavase(R). The Amendment conditions the increase in the purchase price in the Merger upon such Retavase(R) purchase agreement being in full force and effect at the time of the closing of the Merger. The purchase price for the Retavase(R) product rights is approximately $110 million and the agreement includes certain undisclosed milestone payments. ITEM 9.01 FINANCIAL STATEMENTS AND EXHIBITS. (c) Exhibits. Exhibit No. Description - ----------- ----------------------------------------------------- 99.1 Press Release, issued by Protein Design Labs, Inc. on February 1, 2005. 2

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. Date: February 1, 2005 PROTEIN DESIGN LABS, INC. By: /s/ Sergio Garcia-Rodriguez -------------------------------------- Sergio Garcia-Rodriguez Vice President, Legal, General Counsel and Assistant Secretary 3

                                                                    Exhibit 99.1

    PDL TO ADJUST PURCHASE PRICE FOR ESP PHARMA, INC. FOLLOWING ESP PHARMA'S
                      ACQUISITION OF RIGHTS TO RETAVASE(R)

FREMONT, Calif., Feb. 1 /PRNewswire-FirstCall/ -- Protein Design Labs,
Inc. (PDL) (Nasdaq: PDLI) today said that it will amend its definitive
agreement to acquire ESP Pharma, Inc. (ESP) to reflect that company's
acquisition of exclusive rights to Retavase(R) in the United States and
Canada.

On January 25, 2005, PDL and ESP announced that they had entered into a
definitive agreement under which PDL will acquire ESP for $300 million
in cash and approximately $175 million in PDL common stock, or an
aggregate value of approximately $475 million. PDL and ESP have agreed
to increase the purchase price payable to the ESP shareholders at the
closing of the ESP acquisition by $25 million in cash in connection with
the Retavase transaction announced today by ESP. The closing of the
acquisition of ESP is subject to various conditions, including the
receipt of antitrust and other regulatory approvals, and is not
anticipated to close until late in the first quarter of 2005.

"We are extremely pleased by the addition of Retavase to ESP Pharma's
portfolio of proprietary products," said Mark McDade, Chief Executive
Officer, PDL. "We see a strong strategic fit with their hospital-focused
presence in cardiovascular medicine. We also believe that the addition
of Retavase could also help expand sales of Cardene(R) IV, ESP's product
for the short-term reduction of hypertension, due to an increased
presence in hospital emergency rooms." Mr. McDade added, "Overall,
following closing of both ESP and the Retavase transactions, these steps
should accelerate PDL's revenue growth and further enhance the value of
this strategic combination."

ESP Pharma, a specialty pharmaceutical company focused on the
acquisition, marketing, and late-stage development of life-saving
acute-care therapeutics, today announced its acquisition of exclusive
North American rights to Retavase(R) (reteplase) from Centocor, a
biopharmaceutical operating company of Johnson & Johnson. The product
currently is marketed on behalf of Centocor Inc. by Scios, Inc., another
Johnson & Johnson company. ESP Pharma noted that its acquisition of
Retavase included distribution, manufacturing, development and marketing
rights, all relevant intellectual property, and approximately two years
supply of inventory plus certain manufacturing equipment.

First introduced into the U.S. market in 1997, Retavase belongs to the
fibrinolytic or thrombolytic class of pharmaceutical agents used in the
acute-care setting to dissolve coronary blood clots and improve blood
flow in heart attack patients. Each year, in the U.S., more than one
million people suffer a heart attack (acute myocardial infarction or
AMI).

Retavase is indicated for use in the management of AMI in adults for the improvement of ventricular function following AMI, the reduction of the incidence of congestive heart failure, and the reduction of mortality associated with AMI. The product can be administered within a 30-minute time window by a double-bolus injection without dose adjustment for patient weight compared to other thrombolytics requiring longer duration intravenous infusions or dosing adjustments based on weight. About ESP Pharma, Inc. ESP Pharma is committed to Excellence in Specialty Pharmaceuticals and to helping physicians improve patient outcomes and survival in the acute-care setting. Under the leadership of a highly experienced management team, ESP focuses its "Buy and Build, Search and Develop" strategy on identifying opportunities to selectively acquire and enhance the market potential of novel, commercially available therapeutics and late-stage development compounds to fulfill unmet market needs. Additional information about ESP is available at http://www.ESPPharma.com . About PDL Protein Design Labs is a leader in the development of humanized antibodies to prevent or treat various disease conditions. PDL currently has antibodies under development for autoimmune and inflammatory conditions, asthma and cancer. PDL holds fundamental patents for its antibody humanization technology. Further information on PDL is available at www.pdl.com. The foregoing contains forward-looking statements involving risks and uncertainties and PDL's actual results may differ materially from those, express or implied, in the forward-looking statements. The forward-looking statements contained herein include statements about the consummation of the pending acquisition of ESP, and of Retavase assets by ESP, and the benefits of the pending transactions, including their potential effect upon PDL's future financial performance. These statements are subject to inherent risks and uncertainties that could cause actual results to differ materially from those expressed or implied. Such risks and uncertainties include, among others, the possibility that regulatory or other closing conditions will not be satisfied, whether the combined company will be able to realize the anticipated benefits or synergies of the transactions in a timely manner or at all, and the future revenues from ESP Pharma products. Other factors that may cause our actual results to differ materially from those, express or implied, in the forward- looking statements in this press release are discussed in our Annual Report on Form 10-K for the year ended December 31, 2003, in our quarterly report on Form 10-Q for the period ended September 30, 2004, and in other filings with the Securities and Exchange Commission. NOTE: Protein Design Labs and the PDL logo are registered U.S. trademarks of Protein Design Labs, Inc. Cardene IV is a registered trademark of ESP Pharma, Inc. Retavase is a registered trademark of Centocor. SOURCE Protein Design Labs, Inc. -0- 02/01/2005 /CONTACT: James R. Goff Senior Director, Corporate Communications of Protein Design Labs +1-510-574-1421, or jgoff@pdl.com/ /Web site: http://www.pdl.com/