LA JOLLA PHARMACEUTICAL COMPANY ANNOUNCES FINANCING OF UP TO $16.3 MILLION

La Jolla Pharmaceutical Company (OTCBB: LJPC) (the "Company”) announced today that the Company has entered into definitive agreements with institutional investors and affiliates for a private placement of common stock, convertible preferred stock and warrants to purchase convertible preferred stock totaling up to $16.3 million in gross proceeds. The transaction is expected to close on or about May 25, 2010, subject to customary closing conditions. Proceeds of the financing will be used to evaluate potential pharmaceutical products for in-licensing or acquisition and to pursue potential development opportunities for Riquent in light of recent renewed interest in pharmaceutical products being developed by other companies for the treatment of Systemic Lupus Erythematosus (SLE), among other uses.

Summary of Financial Terms

The Company is selling approximately 29.0 million shares of common stock and 5,134 shares of convertible preferred stock in the initial closing, for aggregate gross proceeds of approximately $6.0 million. The investors will also receive a three-year warrant to purchase, for cash, an additional 10,268 shares of convertible preferred stock for an aggregate exercise price of approximately $10.3 million. The investors will be required to exercise the warrants and purchase the additional shares of convertible preferred stock in the event that the Company consummates a strategic transaction approved by the investors.

Each share of convertible preferred stock will be initially convertible into shares of the Company’s common stock at a conversion rate of 66,667 shares of common stock per share of preferred stock that is converted. This conversion rate will be subject to upward adjustment under certain circumstances. The convertible preferred stock will bear a dividend of 15% per annum, payable semi-annually in additional shares of convertible preferred stock. The convertible preferred stock is subject to redemption if the Company does not consummate a strategic transaction approved by the investors within nine months of the initial closing. The Company will be required to obtain the vote of the holders of the convertible preferred stock prior to taking certain corporate actions.

At the initial closing, the investors will also receive an additional three-year warrant to purchase, for cash or on a cashless basis, an additional 5,134 shares of convertible preferred stock for an aggregate exercise price of approximately $5.1 million, if exercised on a cash basis; the Company will receive no cash proceeds and issue fewer shares if the warrants are exercised on a cashless basis. In addition, if the investors purchase the additional 10,268 shares of preferred stock that must be purchased for cash, they will receive an additional three-year warrant to purchase, for cash or on a cashless basis, an additional 10,268 shares of preferred stock on the same terms as provided in the cashless warrants issued at the initial close.

The Company is required to seek stockholder approval in order to secure sufficient shares of common stock to allow for the conversion of the convertible preferred stock. The Company has also agreed to certain limitations on its spending until a strategic transaction is consummated.

Additional terms of this transaction will be disclosed on a Form 8-K to be filed by the Company.

This press release is not an offer to sell or the solicitation of an offer to buy, nor shall there be any sales of the securities in any jurisdiction in which such offer, solicitation, or sale would be unlawful prior to the registration or qualification under the securities laws of any such jurisdiction. The securities were offered in a private placement under Section 4(2) and Regulation D under the Securities Act of 1933, as amended (the "Act”). The securities referenced herein have not been registered under the Act, or any state securities laws, and may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements.

About La Jolla Pharmaceutical Company

La Jolla Pharmaceutical Company is a biopharmaceutical company dedicated to improving and preserving human life by acquiring and developing innovative pharmaceutical products. The Company has historically focused on the development and testing of Riquent as a treatment for lupus nephritis. The Phase 3 clinical trial for Riquent, called the "ASPEN” study, was terminated in February 2009, after the Independent Data Monitoring Board for the ASPEN study informed the Company that they had completed the first interim efficacy analysis and determined that continuing the study was futile. Although continuing the ASPEN study was determined to be futile with respect to the clinical endpoints, Riquent did demonstrate a statistically significant, dose dependent reduction in antibodies to double-stranded DNA when compared to placebo and appeared to be well tolerated. No clinical development activities are ongoing, and the Company is assessing whether there is any potential for further development of Riquent.

Forward-Looking Statement Safe Harbor

This document contains forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. These statements relate to future events or our future results of operation. These statements are only predictions and involve known and unknown risks, uncertainties and other factors, which may cause actual results to be materially different from these forward-looking statements. The Company cautions readers not to place undue reliance on any such forward-looking statements, which speak only as of the date they were made. Certain of these risks, uncertainties, and other factors are described in greater detail in the Company’s filings from time to time with the SEC, including the Current Report on Form 8-K to be filed with a complete description of the terms of this financing, which the Company strongly urges you to read and consider, all of which are available free of charge on the SEC’s web site at http://www.sec.gov. These risks include, but are not limited to, risks relating to the ability to consummate a strategic transaction within the nine month period following closing, the ability to secure the maximum offering proceeds, and risks arising out of covenants and control rights granted to investors in the offering. Subsequent written and oral forward-looking statements attributable to the Company or to persons acting on its behalf are expressly qualified in their entirety by the cautionary statements set forth in the Company’s reports filed with the SEC. The Company expressly disclaims any intent to update any forward-looking statements.