<PAGE>


                                                                     Exhibit 4.2

THE SECURITIES OF SPIROS DEVELOPMENT CORPORATION II, INC., A DELAWARE COMPANY
(THE "COMPANY") EVIDENCED HEREBY ARE SUBJECT TO AN OPTION OF THE HOLDER OF A
MAJORITY OF THE SPECIAL COMMON STOCK OF THE COMPANY, AS DESCRIBED IN THE AMENDED
AND RESTATE CERTIFICATE OF INCORPORATION OF THE COMPANY, TO PURCHASE SUCH
SECURITIES AT AN AGREED UPON PRICE, EXERCISABLE BY NOTICE GIVEN AT ANY TIME
BEGINNING ON THE CLOSING DATE OF THE UNIT OFFERING OF THE CALLABLE COMMON STOCK,
PAR VALUE $0.001 PER SHARE (THE "CALLABLE COMMON STOCK"), OF SPIROS DEVELOPMENT
CORPORATION II, INC. AND THE WARRANTS (THE "WARRANTS") TO PURCHASE ONE-FOURTH OF
ONE COMMON SHARE COMMON SHARES OF DURA PHARMACEUTICALS, INC. ("DURA") AND ENDING
ON THE EARLIER OF (I) DECEMBER 31, 2002, (II) THE 90TH DAY AFTER THE DATE THE
COMPANY PROVIDES SUCH HOLDER WITH QUARTERLY FINANCIAL STATEMENTS OF THE COMPANY
SHOWING CASH OR CASH EQUIVALENTS OF LESS THAN $5,000,000 OR (III) THE DATE OF
TERMINATION BY THE COMPANY OF THAT CERTAIN TECHNOLOGY LICENSE AGREEMENT,
DEVELOPMENT AGREEMENT OR MANUFACTURING AND MARKETING AGREEMENT DATED ON OR ABOUT
DECEMBER 22, 1997. COPIES OF THE AMENDED AND RESTATED CERTIFICATE OF
INCORPORATION OF THE COMPANY ARE AVAILABLE AT THE OFFICES OF THE COMPANY, 7475
LUSK BOULEVARD, SAN DIEGO, CALIFORNIA 92121, ATTENTION: MITCHELL R. WOODBURY AND
WILL BE FURNISHED TO ANY SHAREHOLDER OF THE COMPANY ON REQUEST AND WITHOUT COST.


                     SPIROS DEVELOPMENT CORPORATION II, INC.
              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

                               CUSIP 848936 10 0               CERTIFICATE NO. 1

              FULLY PAID AND NON-ASSESSABLE CALLABLE COMMON STOCK,
                         PAR VALUE OF $.001 PER SHARE OF
                     SPIROS DEVELOPMENT CORPORATION II, INC.

         THIS CERTIFIES that Cede & Co. is the owner of 6,325,000 Shares of
Callable Common Stock of SPIROS DEVELOPMENT CORPORATION II, INC. (the
"Company"), transferable on the books of the Company by the holder hereof, in
person or by duly authorized attorney, upon surrender of this Certificate
properly endorsed. This certificate and the shares represented hereby are
subject to the laws of Delaware, and to the Amended and Restated Certificate of
Incorporation of the Company as now or hereafter amended (copies of which are on
file at the offices of the Company and the Transfer Agent), which are made a
part hereof with the same force and effect as if they were set forth herein, to
all of which the holder, by acceptance hereof, assents. This certificate is not
valid unless countersigned by the Transfer Agent and registered by the
Registrar.

         IN WITNESS WHEREOF, the Company has caused the signatures of its duly
authorized officers and the of its corporate seal to be hereunto affixed.

         Dated:  January 1, 2000

                          SPIROS DEVELOPMENT CORPORATION II, INC.,
                          a Delaware corporation

                          By:   /s/ David S. Kabakoff
                             ---------------------------------------------------
                                 David S. Kabakoff
                                 Chairman, President and Chief Executive Officer

                          By:   /s/ John R. Cook
                             ---------------------------------------------------
                                 John R. Cook
                                 Secretary

Transfer Agent and Registrar:
CHASEMELLON SHAREHOLDER SERVICES, L.L.C.

By:    /s/ Brenda Buth
   ------------------------------
Name:       Brenda Buth
     ----------------------------
Title:      Unit Manager
     ----------------------------


<PAGE>


         The Company will furnish without charge to each stockholder who so
requests the powers, designations, preferences and relative participating,
optional, or other special rights of each class of stock or series thereof and
the qualifications, limitations or restrictions of such preferences and/or
rights. Such requests shall be made to the Company's Secretary at the principal
office of the Company.

         The following abbreviations, when used in the inscription on the face
of this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

TEN COM    -   as tenants in common
TEN ENT    -   as tenants by the entireties
JT TEN     -   as joint tenants with right of survivorship and not as tenants in
               common

UNIF GIFT MIN ACT                  Custodian
                  -----------               ------------------------------------
                    (Cust)                                 (Minor)
                    under Uniform Gifts to Minors Act
                                                     ---------------------------
                                                               (State)

UNIF TRF MIN ACT                   Custodian (until age                        )
                  -----------                          ------------------------
                    (Cust)
                                                        under Uniform Transfers
                    -----------------------------------
                    (Minor)
                    to Minors Act
                                 -----------------------------------------------
                                                     (State)

Additional abbreviations may also be used though not in the above list.

         For Value Received, ________________________ hereby sell, assign and
transfer unto


Please insert Social Security or Other
Identifying Number of Assignee:


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


--------------------------------------------------------------------------------
(please print or typewrite name and address, including zip code, or assignee)


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

__________________________________________________ Shares of the Callable Common
Stock represented by the Certificate within, and do hereby irrevocably
constitute and appoint___________________ Attorney, to transfer the said same on
the books of the within named Company, with full power of substitution in the
premises.

Dated:
       -------------------
                                       -----------------------------------------
                                       Signature

                                       -----------------------------------------
                                       Signature

                                       Notice: The signature(s) to
                                       this assignment must correspond
                                       with the name as written upon
                                       the face of the Certificate, in
                                       every particular, without
                                       alteration or enlargement, or
                                       any change whatever.



Signature(s) Guaranteed:



By:
   ------------------------------------------------
The signature must be guaranteed by an eligible
guarantor institution (banks, stockbrokers, savings
and loan associations and credit unions with member-
ship in an approved signature guarantee medallion
program), pursuant to S.E.C. Rule 17Ad-15.