NABI BIOPHARMACEUTICALS 2.875% Convertible Senior Notes due 2025

Exhibit 4.8

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY (AND ANY PAYMENT HEREON IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS TO NOMINEES OF THE DEPOSITORY TRUST COMPANY, OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN ARTICLE TWO OF THE INDENTURE REFERRED TO ON THE REVERSE HEREOF.

The foregoing legend may be removed from this Security on satisfaction of the conditions specified in the Indenture.

N ABI B IOPHARMACEUTICALS

2.875% Convertible Senior Notes due 2025

Nabi Biopharmaceuticals, a Delaware corporation, promises to pay to Cede & Co. or registered assigns, the principal amount of ZERO DOLLARS AND NO CENTS ($0.00) on April 15, 2025 or such greater or lesser amount as is indicated on the Schedule of Increases and Decreases of Global Security attached to this Security.

Interest Payment Dates: April 15 and October 15, commencing October 15, 2005.

Record Dates: April 1 and October 1.

Reference is hereby made to the further provisions of this Security set forth on the reverse side of this Security, which further provisions shall for all purposes have the same effect as if set forth at this place.

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IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: August 10, 2005

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

U.S. BANK NATIONAL ASSOCIATION

as Trustee, certifies that this is one of the Securities

referred to in the within mentioned Indenture.

Dated: August 10, 2005

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REVERSE OF NOTE

2.875% Convertible Senior Notes due 2025

This Security is one of a duly authorized issue of the 2.875% Convertible Senior Notes due 2025 (the “ Securities ”) of Nabi Biopharmaceuticals, a Delaware corporation (including any successor corporation under the Indenture hereinafter referred to, the “ Company ”), issued under an Indenture, dated as of April 19, 2005 (the “ Indenture ”), between the Company and U.S. Bank National Association, as trustee (the “ Trustee ”). The terms of the Security include those stated in the Indenture, those made part of the Indenture by reference to the Trust Indenture Act of 1939, as amended (“ TIA ”), and those set forth in this Security. This Security is subject to all such terms, and Holders are referred to the Indenture and the TIA for a statement of all such terms. To the extent permitted by applicable law, in the event of any inconsistency between the terms of this Security and the terms of the Indenture, the terms of the Indenture shall control. Capitalized terms used but not defined herein have the meanings assigned to them in the Indenture referred to below unless otherwise indicated.

1. Interest.

The Company promises to pay interest on the principal amount of the Securities at the interest rate of 2.875% per annum (the “ Interest Rate ”) from the date of issuance until repayment in full at April 15, 2025, or until an earlier conversion, redemption or repurchase. The Company will pay interest on this Security semi-annually in arrears on April 15 and October 15 of each year (each, an “ interest payment date ”), commencing October 15, 2005.

The Securities shall bear interest from April 19, 2005 until the principal amount thereof is paid or made available for payment, or until such date on which the Securities are converted, redeemed or purchased as provided herein at the Interest Rate.

Interest on the Securities shall be computed (i) for any full semi-annual period for which the Interest Rate is applicable, on the basis of a 360-day year of twelve 30-day months and (ii) for any period for which the Interest Rate is applicable for less than a full semi-annual period for which interest is calculated, on the basis of a 30-day month and, for such periods of less than a month, the actual number of days elapsed over a 30-day month.

If this Security is redeemed or repurchased by the Company on a date that is after the record date and on or prior to the corresponding interest payment date, interest and Liquidated Damages, if any, accrued and unpaid hereon to but not including the applicable Redemption Date, Repurchase Date or Fundamental Change Purchase Date, as the case may be, will be paid to the same Holder to whom the Company pays the principal of this Security.

Interest on Securities converted after a record date but prior to the corresponding interest payment date will be paid to the Holder of the Securities on the record date but, upon conversion, the Holder must pay the Company the interest and Liquidated Damages, if any, which have accrued and will be paid on such interest payment date; provided , that no such payment need be made with respect to Securities which will be redeemed or repurchased by the Company after a record date and on or prior to the third Business Day after the corresponding interest payment date.

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If the principal amount hereof or any portion of such principal amount or any interest, including Liquidated Damages, if any, on any Security is not paid when due (whether upon acceleration pursuant to Section 6.2 of the Indenture, upon the date set for payment of the Redemption Price pursuant to Section 3.1 of the Indenture or the Repurchase Price or the Fundamental Change Purchase Price pursuant to Section 3.7 or Section 3.11 of the Indenture, as the case may be, or upon the Stated Maturity of this Security), then in each such case the overdue amount shall, to the extent permitted by law, bear interest at the Interest Rate, compounded semi-annually, which interest shall accrue from the date on which such overdue amount was originally due until the date on which payment of such amount, including interest thereon, has been made or duly provided for. All such interest shall be payable on demand.

2. Method of Payment.

Except as provided below, interest will be paid (i) on the Global Securities to The Depository Trust Company (“ DTC ”) or its nominee in immediately available funds, (ii) on any definitive Securities having an aggregate principal amount of $2,000,000 or less, by check mailed to the Holders of such Securities, and (iii) on any definitive Securities having an aggregate principal amount of more than $2,000,000, by wire transfer in immediately available funds at the election of the Holders of such Securities.

At Stated Maturity, the Company will pay interest on definitive Securities at the Company’s office or agency in New York City, which initially will be the corporate trust office of U.S. Bank National Association, in New York City.

Principal on Global Securities will be paid to DTC or its nominee in immediately available funds. Principal on definitive Securities will be payable, upon Stated Maturity or when due, at the office or agency of the Company in New York City, maintained for such purpose, initially the corporate trust office of U.S. Bank National Association, in New York City.

Subject to the terms and conditions of the Indenture, the Company will make payments in cash in respect of Redemption Prices, Repurchase Prices, Fundamental Change Purchase Prices and at Stated Maturity to Holders who surrender Securities to a Paying Agent to collect such payments in respect of the Securities. The Company will pay cash amounts in money of the United States that at the time of payment is legal tender for payment of public and private debts. However, the Company may make such cash payments by check payable in such money, subject to the terms of the Indenture.

3. Paying Agent, Conversion Agent and Registrar.

Initially, U.S. Bank National Association will act as Paying Agent, Conversion Agent and Registrar. The Company may appoint and change any Paying Agent, Conversion Agent or Registrar without notice, other than notice to the Trustee; provided that the Company will maintain at least one Paying Agent in the State of New York, City of New York, Borough of Manhattan, which shall initially be an office or agency of the Trustee. The Company or any of its Subsidiaries or any of their Affiliates may act as Paying Agent, Conversion Agent or Registrar.

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4. Indenture.

The Securities are senior unsecured obligations of the Company initially limited to $100,000,000 aggregate principal amount (or such greater amount necessary to reflect the exercise by the Initial Purchasers of their option to purchase additional Securities in compliance with the Purchase Agreement, but not in excess of $120,000,000).

The Company may, without the consent of the Holders of the Securities, increase the Principal Amount of the Securities by issuing additional securities in the future on the same terms and conditions, except for any differences in the issue price and interest accrued prior to the issue date of the additional securities, provided, that such difference does not cause the additional se