<PAGE>   1
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D


                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                                (AMENDMENT NO.4)*


                        IDEC PHARMACEUTICALS CORPORATION
- --------------------------------------------------------------------------------
                                (Name of Issuer)


                           Common Stock, No Par Value
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    004493701
- --------------------------------------------------------------------------------
                                 (CUSIP Number)

                Donald F. Parman, SmithKline Beecham Corporation
                   One Franklin Plaza, Philadelphia, PA 19102
                             Telephone 215-751-7633
- --------------------------------------------------------------------------------
           (Name, Address and Telephone Number of Person Authorized to
                       Receive Notices and Communications)


                                  March 7, 1997
- --------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

Check the following box if a fee is being paid with the statement / /. (A fee is
not required only if the reporting person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)

Note: Six copies of this statement, including all exhibits, should be filed with
the Commission. See Rule 13d-1(a) for other parties to whom copies are to be
sent.

*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 on 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).

<PAGE>   2
                                  SCHEDULE 13D

CUSIP NO. 857304100                                            PAGE 2 OF 6 PAGES
- --------------------------------------------------------------------------------

This Amendment No. 4 amends and supplements the Statement on Schedule 13D
manually filed with the Securities and Exchange Commission (the "Commission") on
April 24, 1995 (the "Initial Statement") filed jointly by SmithKline Beecham
plc, SmithKline Beecham Corporation, and S.R. One, Limited; Amendment No. 1
electronically filed on September 26, 1996; Amendment No. 2 electronically filed
on December 13, 1996; and Amendment No. 3 electronically filed on March 3, 1997
with respect to ownership of securities of IDEC Pharmaceuticals Corporation.

The undersigned hereby amends and supplements Item 5 of the Initial Statement by
the following information (capitalized terms used herein without definition
shall have the same meaning as set forth in the Initial Statement.) Since the
reporting person now holds less than 5% with this filing, further reporting
under Schedule 13-D is no longer required.

<PAGE>   3
                                  SCHEDULE 13D

CUSIP NO. 0004493701                                           Page 2 of 5 Pages
- --------------------------------------------------------------------------------

1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

         SmithKline Beecham Corporation
         23-1099050
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                        (a) / /
                                                                        (b) / /
- --------------------------------------------------------------------------------
3   SEC USE ONLY


- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

         WC
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEMS 2(D) OR 2(E)                                                    / /

- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION

         Pennsylvania

- --------------------------------------------------------------------------------
                7   SOLE VOTING POWER
  NUMBER OF
   SHARES                  638,360
BENEFICIALLY   -----------------------------------------------------------------
  OWNED BY      8   SHARED VOTING POWER
   EACH
 REPORTING                 None
  PERSON       -----------------------------------------------------------------
   WITH         9   SOLE DISPOSITIVE POWER

                           638,360
               -----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER

                           None
- --------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

         638,360
- --------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
     CERTAIN SHARES*                                                         / /

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

         3.5%
- --------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

         CO
- --------------------------------------------------------------------------------

<PAGE>   4
                                                               Page 3 of 5 Pages




Item 1.  Security and Issuer.


Item 2.  Identity and Background.


Item 3.  Source and Amount of Funds or Other Consideration.



Item 4.  Purpose of Transaction.

<PAGE>   5
                                                               Page 4 of 5 Pages







Item 5.  Interest in Securities of the Issuer.

                  (a)  Amount and Percent Beneficially Owned


<TABLE>
<CAPTION>
                           Registered Name                     No. of Shares    Percent

<S>                                                                 <C>          <C>
                           SmithKline Beecham Corporation           638,360       3.5%
</TABLE>



                  (b)

                  (c) The reporting persons sold 467,500 shares of Common Stock
in the open market in the following manner:


<TABLE>
<CAPTION>
Registered Name                       Transaction Date      Number of Share    Price Per Share

<S>                                   <C>                       <C>                <C>  
SmithKline Beecham Corporation        March 4, 1997              30,000             24.50
SmithKline Beecham Corporation        March 5, 1997              15,000             24.50
SmithKline Beecham Corporation        March 6, 1997              12,500             24.50
SmithKline Beecham Corporation        March 6, 1997               7,500            24.625
SmithKline Beecham Corporation        March 7, 1997              40,000            24.875
SmithKline Beecham Corporation        March 7, 1997              40,000             25.00
SmithKline Beecham Corporation        March 7, 1997              10,000             25.25
SmithKline Beecham Corporation        March 7, 1997              10,000            25.375
SmithKline Beecham Corporation        March 7, 1997              25,000             25.50
SmithKline Beecham Corporation        March 7, 1997              12,500            25,625
SmithKline Beecham Corporation        March 7, 1997               5,000             25.75
SmithKline Beecham Corporation        March 7, 1997              45,000            25.875
SmithKline Beecham Corporation        March 10, 1997             12,500            26.125
SmithKline Beecham Corporation        March 11, 1997            165,000             29.50
SmithKline Beecham Corporation        March 11, 1997             10,000            29.625
SmithKline Beecham Corporation        March 11, 1997             25,000             30.00
SmithKline Beecham Corporation        March 14, 1997              2,500             28.50
                                                           ------------
                                                                467,500
</TABLE>


                 (d)

                 (e)

Item 6.           Contracts, Arrangements, Understandings or
                  Relationship With respect to Securities of the Issuer.



Item 7.           Materials to be Filed as Exhibits.

<PAGE>   6
                                                               Page 5 of 5 Pages




                               SIGNATURE

                  After reasonable inquiry and to the best of my knowledge and
belief, the undersigned certifies that the information set forth in the
Statement is true, correct and complete.



                                    SMITHKLINE BEECHAM CORPORATION


                                    By:      /s/Donald F. Parman
                                       ------------------------------
                                        Donald F. Parman
                                        Secretary




DATED:  March 17, 1997