Clinical Pharmacology of TOCOSOL Paclitaxel Cancer Drug to be Presented at American Society of Clinical Oncology -- ASCO -- Annual Meeting.

BOTHELL, Wash. -- Sonus Pharmaceuticals, Inc. (Nasdaq:SNUS) today announced that the American Society of Clinical Oncology (ASCO) has selected a clinical pharmacology study of the Company's lead oncology candidate, TOCOSOL(R) Paclitaxel, a novel vitamin-E based emulsion formulation of the leading anti-cancer drug paclitaxel, for presentation at the ASCO Annual Meeting in Orlando, Florida, May 13-17. The study, involving 36 patients with advanced cancers, compared the pharmacokinetics and acute safety of paclitaxel given as TOCOSOL Paclitaxel and as Taxol(R). The leading investigator for the clinical study, Prof. A.-R. Hanauske of the St. Georg Hospital, Hamburg, Germany, will make the presentation at the Developmental Therapeutics Poster Session on Sunday, May 15, at 8:00 a.m. in Hall C of the Orange County Convention Center.

The clinical pharmacology study included analyses of the amount of paclitaxel in the blood circulation following single doses of TOCOSOL Paclitaxel and Taxol. Both drugs were administered at the standard Taxol regimen of 175 mg/m(2) separated by at least three weeks, and TOCOSOL Paclitaxel delivered substantially more active paclitaxel into the circulation. Changes in blood cell counts and other side effects were also carefully monitored. Full results of the study, including details of the pharmacokinetics of paclitaxel in its bound and active unbound forms, and the side effects observed for both drugs, will be the subject of the presentation at ASCO.

"This clinical pharmacology study is one of the most comprehensive studies ever done for paclitaxel. We believe that TOCOSOL Paclitaxel may ultimately be shown to provide better efficacy for cancer patients," said Michael B. Stewart, M.D., Chief Medical Officer of Sonus Pharmaceuticals. "Coupled with what we have already seen from Phase 2a studies about the ease of use and tolerability of TOCOSOL Paclitaxel given weekly for extended periods of time, we believe that we are building a compelling argument that TOCOSOL Paclitaxel will be the taxane of choice for patients and physicians, if it is approved. We are eager to confirm the potential benefits of TOCOSOL Paclitaxel in the pivotal Phase 3 trial, which we expect to initiate in 2005."

About TOCOSOL Paclitaxel

Sonus has completed patient enrollment in Phase 2a studies of TOCOSOL Paclitaxel in bladder, ovarian, and lung cancer patients, and those trials have generated encouraging data on safety and anti-tumor activity, which were reported at the ASCO Annual Meeting in 2004. Phase 2b studies of TOCOSOL Paclitaxel are ongoing in breast and bladder cancers. TOCOSOL Paclitaxel offers the convenience of a ready-to-use formulation that does not require reconstitution, dilution or pharmacy preparation as is required with the marketed paclitaxel products. Additionally, TOCOSOL Paclitaxel is administered to patients in a short 15-minute infusion, compared to the prolonged 3-hour infusion required for Taxol.

About Sonus Pharmaceuticals, Inc.

Headquartered near Seattle, Sonus Pharmaceuticals is focused on the development of therapeutic drugs that may offer improved administration, safety, tolerability and effectiveness for the treatment of cancer and related therapies. The Company's lead product candidate is TOCOSOL(R) Paclitaxel, a new formulation of the widely prescribed anti-cancer drug paclitaxel. In addition to executing its plans for TOCOSOL Paclitaxel, Sonus remains focused on driving product and corporate development activities towards building and expanding its pipeline of oncology and related product candidates. For additional information, including news releases, please visit the Company's web site at www.sonuspharma.com.

Safe Harbor 

Certain statements made in this press release are forward-looking such as those, among others, relating to the development, safety and efficacy of drug delivery products and potential applications for these products. As discussed in Sonus Pharmaceuticals' filings with the Securities and Exchange Commission, including its Annual Report on Form 10-K filed on March 12, 2004 and Quarterly Report on Form 10-Q filed November 15, 2004, actual results could differ materially from those projected in the forward-looking statements as a result of the following factors, among others: the Company's products will require extensive clinical testing and approval by regulatory authorities; such approvals are lengthy and expensive and may never occur; risks that the Company may not be successful in obtaining funding from third parties or completing a financing necessary to support the costs and expenses of clinical studies; risks that clinical studies with TOCOSOL Paclitaxel will not be successful; risks that the FDA may not approve the Company's proposed New Drug Application; and risks of successful development of additional drug delivery products. Sonus undertakes no obligation to update the forward-looking statements contained herein or to reflect events or circumstances occurring after the date hereof.

Taxol(R) is a registered trademark of Bristol-Myers Squibb Company.