Clinical Efficacy Data on FACTIVE Tablets for Treatment of Acute Bacterial Rhinosinusitis Presented at Infectious Diseases Society of America Meeting.

BOSTON -- - Primary endpoints in Phase III trials met -

Data presented at the 42nd Annual Meeting of the Infectious Diseases Society of America (IDSA) showed that in two Phase III clinical trials once-daily FACTIVE(R) (gemifloxacin mesylate) tablets (320 mg) given for five days met the primary endpoints for the treatment of acute bacterial rhinosinusitis (ABS), including infections due to penicillin-resistant S. pneumoniae. FACTIVE tablets are the newest antibiotics in the fluoroquinolone class to be made available for the treatment of acute bacterial exacerbations of chronic bronchitis (AECB) and mild to moderate community-acquired pneumonia (CAP).

The first study presented at this year's IDSA was a randomized, double-blind trial that evaluated the safety and efficacy of once-daily FACTIVE (320 mg) tablets for either five or seven days in patients ages 18 to 80. In this study clinical success, sufficient improvement or resolution of signs and symptoms, at follow-up, the primary efficacy endpoint, was 87.3% and 86.9% for FACTIVE five and seven day, respectively (in 356 total per protocol patients; previously reported as a treatment difference of 0.44%, 95% confidence interval: -6.54 to 7.41).

The other study assessed bacteriologic and clinical efficacy and safety of once-daily FACTIVE tablets for five days in patients ages 16 to 81. In this study bacteriologic success, or the eradication or presumed eradication of all initial pathogens without any new infections, at follow-up, the primary endpoint, was 90.3% (195/216) (95% CI: 86.33, 94.23). At follow-up, there was a 100% (8/8) clinical success and bacteriological eradication rate for penicillin-resistant isolates of S. pneumoniae from patients in the study. Of the 687 patients treated for five days in both studies, the most common adverse events were nausea (3.1%), diarrhea (2.9%), headache (2.2%) and rash (1.6%).

"FACTIVE tablets are the first fluoroquinolone to meet clinical effectiveness endpoints in a broad-based clinical trial for the treatment of patients with sinusitis with only five days of treatment," said Jack Anon, MD, lead investigator and Clinical Professor, The University of Pittsburgh School of Medicine, Department of Otolaryngology. "These data on FACTIVE tablets' broad spectrum and potent activity against the key pathogens associated with ABS, along with the short treatment regimen, show its promise as a treatment of these common infections, potentially helping patients more quickly regain their quality of life."

The results of these previously completed Phase III clinical trials, together with two head-to-head comparator Phase III trials completed for the treatment of ABS with FACTIVE tablets not presented at this conference, form the basis of a planned regulatory submission to the FDA for this indication next year, contingent on the outcome of discussions with the FDA. Currently, the Company is gathering additional data on the market experience of FACTIVE tablets to be included in the filing.

An estimated 20 million cases of ABS occur annually in the U.S., and sinusitis accounts for about 22% of all adult antibiotic prescriptions resulting in a yearly cost of more than $3.5 billion. If untreated or inadequately treated, acute sinusitis may become chronic.

"Oscient is committed to exploring the full therapeutic potential of FACTIVE tablets," said Gary Patou, Chief Medical Officer of Oscient Pharmaceuticals. "Since high levels of antimicrobial resistance are now being detected in the principal pathogens that cause ABS including S. pneumoniae, we are encouraged by the response rates of FACTIVE tablets in these studies and anticipate seeking approval for this potentially important new treatment option for the medical community."

FACTIVE Clinical Studies

Oscient is conducting a Phase III trial of FACTIVE tablets for the potential treatment of CAP in five days and developing an intravenous formulation for the potential treatment of patients hospitalized with severe CAP. FACTIVE is not approved for either severe CAP, five-day CAP or ABS.

The safety and efficacy of FACTIVE tablets were established through a robust clinical development program involving 6,775 patients. In these studies, FACTIVE tablets demonstrated excellent clinical response rates at test-of-cure visits for CAP and AECB performing as well as comparators including clarithromycin, levofloxacin, amoxicillin/clavulanate, ceftriaxone and oral cefuroxime.

Important Safety Information about FACTIVE Tablets

In clinical trials, the discontinuation rate due to related adverse events was similar for FACTIVE tablets and comparators (2.2% versus 2.1%, respectively). The most common (more than 2% incidence) side effects reported in FACTIVE clinical trials were diarrhea (3.6%), rash (2.8%) and nausea (2.7%). In clinical trials, rash was reported in 2.8% of patients receiving gemifloxacin and was more commonly observed in patients less than 40 years of age, especially females. The incidence of rash increases with treatment longer than the maximum-labeled duration of 7 days.

Gemifloxacin is contraindicated in patients with a history of hypersensitivity to gemifloxacin, fluoroquinolone antibiotic agents, or any of the product components. To reduce the development of drug-resistant bacteria and maintain the effectiveness of FACTIVE tablets and other antibacterial drugs, FACTIVE tablets should be used only to treat infections that are proven or strongly suspected to be caused by bacteria.

Patients receiving marketed fluoroquinolones have reported serious and occasionally fatal hypersensitivity and/or anaphylactic reactions, peripheral neuropathy, and tendon ruptures. These adverse events have not been reported by patients taking gemifloxacin. However, gemifloxacin should be discontinued immediately at the first sign of any of these events.

Gemifloxacin may prolong the QT interval in some patients. Gemifloxacin should be avoided in patients with a history of prolongation of the QTc interval, patients with uncorrected electrolyte disorders (hypokalemia or hypomagnesemia), and patients receiving Class IA or Class III antiarrhythmic agents.

In clinical studies with gemifloxacin, CNS effects have been reported infrequently. As with other fluoroquinolones, gemifloxacin should be used with caution in patients with known or suspected CNS diseases. If CNS reactions occur, gemifloxacin should be discontinued and appropriate measures instituted.

No significant drug-drug interactions were seen with theophylline, digoxin, oral contraceptives, cimetidine, omeprazole, and warfarin, although patients receiving a fluoroquinolone concomitantly with warfarin should be monitored closely. Drug-drug interactions include probenicid, sucralfate, antacids containing aluminum or magnesium, iron, multivitamins containing metal cations, and didanosine.

The safety and effectiveness of gemifloxacin in children, adolescents (less than 18 years of age), pregnant women, and lactating women have not been established. For complete safety and efficacy information, please see the full prescribing information available at www.FACTIVE.com.

About Oscient Pharmaceuticals

Oscient Pharmaceuticals Corporation (Nasdaq: OSCI) is a biopharmaceutical company committed to the clinical development and commercialization of novel therapeutics to address unmet medical needs. The Company is marketing FACTIVE(R) (gemifloxacin mesylate) tablets, approved by the FDA for the treatment of acute bacterial exacerbations of chronic bronchitis and community-acquired pneumonia of mild to moderate severity. In addition to the oral tablet form, Oscient Pharmaceuticals is developing an investigational FACTIVE intravenous formulation for use in hospitalized patients.

The Company has a novel antibiotic candidate, Ramoplanin, in advanced clinical development for the treatment of Clostridium difficile-associated diarrhea (CDAD). The Company's preclinical program includes an oral peptide deformylase (PDF) inhibitor series, under preclinical development for community-based respiratory tract infections.

Forward-Looking Statement

This news release may contain forward-looking statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements represent our management's judgment regarding future events. Forward-looking statements typically are identified by use of terms such as "may," "will," "should," "plan," "expect," "intend," "anticipate," "estimate," and similar words, although some forward-looking statements are expressed differently. We do not plan to update these forward-looking statements. You should be aware that our actual results could differ materially from those contained in the forward-looking statements due to a number of risks affecting our business. Our business is significantly dependent upon our ability to launch the commercial sale of FACTIVE(R) tablets, and, due to the limitations on our resources and experience in commercializing products, there can be no assurance that we will be able to successfully launch FACTIVE tablets. Even if we succeed in launching FACTIVE tablets, a number of factors could negatively affect the success of FACTIVE tablets, including lack of acceptance by physicians, patients and third party payors, unanticipated safety, efficacy, or other regulatory issues, problems relating to manufacturing or supply and competition from other products. It is also uncertain whether we will be able to expand the indications for which FACTIVE tablets are approved or obtain approval to sell our lead product candidate, Ramoplanin. Factors which may prevent or delay us in obtaining additional regulatory approvals of our products and product candidates include, negative, inconclusive or insufficient results in ongoing or future clinical trials, delays in the progress of ongoing clinical trials and safety concerns arising with respect to our products or product candidates. We are also subject to the risk that our business and the business of Genesoft Pharmaceuticals will not be integrated successfully and the significant costs related to the integration. Our business could also be negatively affected due to our inability or the inability of our alliance partners to successfully develop and commercialize products based on our discoveries. Additional factors that could cause actual results to differ materially from those projected or suggested in any forward looking statement are set forth in Exhibit 99.1 to the Company's Quarterly Report on Form 10-Q for the quarter ending June 26, 2004 and in other filings that we may make with the Securities and Exchange Commission from time to time.