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                                                                     EXHIBIT 4.1

THIS NOTE AND THE SECURITIES ISSUABLE UPON CONVERSION OF THIS NOTE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES
LAWS AND MAY NOT BE TRANSFERRED, SOLD OR OFFERED FOR SALE EXCEPT PURSUANT TO AN
EFFECTIVE REGISTRATION STATEMENT AS TO THIS NOTE UNDER SAID ACT AND ANY
APPLICABLE STATE SECURITIES LAWS OR AN OPINION OF COUNSEL REASONABLY
SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

$________                                              OCTOBER 15, 1999
                                                       WILMINGTON, MASSACHUSETTS

         FOR VALUE RECEIVED, ASCENT PEDIATRICS, INC., a Delaware corporation
(the "undersigned"), hereby promises to pay to the order of ____________, or
registered assigns, the principal amount of ______________, or if less, the
aggregate unpaid amount of all Advances made to the undersigned under the Fourth
Amendment (as defined below), on July 1, 2004, and to pay interest from the date
hereof (computed on the basis of a 360-day year of twelve 30-day months) on the
unpaid principal amount outstanding hereof at the rate of 7.5% per annum until
the unpaid principal amount outstanding hereunder shall become due and payable,
and to pay, on demand, interest on any overdue principal, including any overdue
prepayment of principal and premium, if any, at the rate of 12% per annum.

         Schedule A attached hereto and incorporated herein by reference records
(i) the date and amount of each Advance hereunder and (ii) the date and amount
of any principal and interest payments made by the Company hereunder; provided
however that any failure to endorse such information on such Schedule or
continuation thereof shall not in any manner affect the obligation of the
Company to make payments of principal and interest in accordance with the terms
of this Note.

         Payments of principal, premium, if any, and interest shall be made to
the registered holder hereof in such coin or currency of the United States of
America as at the time of payment shall be legal tender for the payment of
public and private debts, at the office of the Company at 187 Ballardvale
Street, Suite B125, Wilmington, Massachusetts 01887, subject to the right of the
registered holder hereof under the Fourth Amendment to receive direct payment in
immediately available funds.

         Accrued interest shall be paid by the undersigned quarterly on March
31, June 30, September 30 and December 31 of each year, commencing on December
31, 1999.

         If any amounts under this Note become due and payable on a Saturday or
Sunday or a day on which banks in the State of New York or the Commonwealth of
Massachusetts are authorized by law to remain closed, such amounts shall be paid
on the next succeeding day that such banks shall be open for business.


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         This Note has been issued pursuant to, and is one of a series of notes
(the "Fourth Amendment Convertible Notes") issued pursuant to the Fourth
Amendment dated as of October 15, 1999 (the "Fourth Amendment") to the
Securities Purchase Agreement dated as of May 13, 1998 between the undersigned
and the Purchasers named therein, as amended (such Securities Purchase
Agreement, as amended on September 30, 1998, February 16, 1999 and July 1, 1999
and by the Fourth Amendment being referred to herein as the "Purchase
Agreement"). This Note is subject to and entitled to the benefits of all of the
provisions of the Purchase Agreement. Capitalized terms herein are used as
defined in the Purchase Agreement unless otherwise defined herein.

         This Note may be redeemed by either the undersigned or the holder as
provided in Article IX of the Purchase Agreement. This Note may, or in certain
circumstances, shall automatically, be converted into Depositary Shares or other
securities of the Company in accordance with Section 12.2 of the Purchase
Agreement.

         This Note is a general unsecured obligation of the undersigned and is
subordinated to all Senior Indebtedness in accordance with Article XI of the
Purchase Agreement and, as provided under Article XI, in certain circumstances,
to Senior Indebtedness under the Subordination Agreement dated as of February
16, 1999 among the Company, Alpharma USPD Inc. and the Original Lenders named
therein, as amended. Upon the occurrence of any one or more Events of Default,
all amounts then remaining unpaid on this Note may be declared to be immediately
due and payable subject to and as provided in the Purchase Agreement.

         This Note may be amended and the provisions hereof may be waived only
in accordance with Article XIV of the Purchase Agreement.

         This Note shall be governed by and construed in accordance with the
laws of the State of New York.

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         IN WITNESS WHEREOF, ASCENT PEDIATRICS, INC. has caused this Note
to be duly executed.

                                                  ASCENT PEDIATRICS, INC.



                                                  By: _________________
                                                  Name: Emmett Clemente
                                                  Title:   Chairman


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