FDA Accepts as "Complete Response" Oscient Pharmaceuticals' Submission Following FACTIVE Approvable Letter for Five-Day CAP.

WALTHAM, Mass. -- The U.S. Food and Drug Administration (FDA) has accepted as complete Oscient Pharmaceuticals Corporation's (Nasdaq: OSCI) response to the FACTIVE([R])(gemifloxacin mesylate) tablets approvable letter for the application seeking approval for the five-day treatment of community-acquired pneumonia of mild to moderate severity (CAP). FACTIVE is currently approved by the FDA for the five-day treatment of acute exacerbations of chronic bronchitis (AECB) and the seven-day treatment of CAP.

The approvable letter, received on September 21, 2006, asked for clarification and additional interpretation regarding certain data included in the application to assist the FDA in its evaluation. Oscient submitted its response to the approvable letter last month. The FDA has classified the complete response as a Class II resubmission with a user fee deadline of May 1, 2007.

"We are looking forward to working with the FDA through this final phase of review of our five-day CAP application," stated Steven M. Rauscher, President and CEO.

The NDA for the five-day treatment of CAP contained data from a successful Phase III trial completed in 2005 comparing a five-day and seven-day treatment with FACTIVE 320 mg once-daily for CAP in 510 patients. That study demonstrated strong clinical response rates at follow up (the primary endpoint) in both arms. Currently, no fluoroquinolone is approved for the five-day treatment of both AECB and CAP. Community-acquired pneumonia is a common and serious illness in the United States with three to four million cases per year, resulting in approximately one million hospitalizations and 40,000 deaths annually. Pneumonia is the most common cause of death due to an infectious disease.

About Oscient Pharmaceuticals

Oscient Pharmaceuticals Corporation is a commercial-stage biopharmaceutical company marketing two FDA-approved products with its national primary care sales force. ANTARA([R]) 130 mg (fenofibrate) capsules is indicated for the adjunct treatment of hypercholesterolemia (high blood cholesterol) and hypertriglyceridemia (high triglycerides) in combination with diet. FACTIVE([R]) (gemifloxacin mesylate) tablets is an antibiotic approved for the treatment of acute bacterial exacerbations of chronic bronchitis and community-acquired pneumonia of mild to moderate severity. Oscient also has a novel, late-stage antibiotic candidate, Ramoplanin, under investigation for the treatment of Clostridium difficile-associated disease (CDAD).

For important information regarding the safety and use of ANTARA and FACTIVE, please see the full prescribing information available at www.antararx.com and www.factive.com.

Important Safety Information about FACTIVE Tablets

The most common (more than 2% incidence) drug-related side effects reported in FACTIVE clinical trials were diarrhea (3.6%), rash (2.8%) and nausea (2.7%). In clinical trials, drug-related 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. In clinical trials, the discontinuation rate due to drug-related adverse events was similar for FACTIVE tablets and comparators (2.2% versus 2.1%, respectively).

Gemifloxacin is contraindicated in patients with a history of hypersensitivity to gemifloxacin, fluoroquinolone antibiotic agents, or any of the product components. Patients receiving marketed fluoroquinolones have reported serious and occasionally fatal hypersensitivity and/or anaphylactic reactions, peripheral neuropathy, antibiotic-associated colitis and tendon ruptures. Gemifloxacin should be discontinued immediately at the first sign of any of these events.

Fluoroquinolones 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.

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, including statements regarding the timing of FDA's response to our resubmission of our sNDA seeking approval for the five-day treatment of CAP. 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. These risks include, but are not limited to (i) our ability to successfully commercialize and market ANTARA or FACTIVE due to: the limitations on our resources and experience in the commercialization of products; lack of acceptance by physicians, patients and third party payors; unanticipated safety, product liability, efficacy, or other regulatory issues; delays in recruiting and training sales personnel; problems relating to manufacturing or supply; inadequate distribution of the products by wholesalers, pharmacies, hospitals and other customers; and competition from other products; (ii) our ability to integrate ANTARA into our business; (iii) whether we will be able to expand the indications for which FACTIVE is approved; (iv) the delay or inability to find sublicensing partners for FACTIVE or to negotiate favorable licensing terms; (v) the delay in or inability to obtain additional regulatory approvals of our products and product candidates due to negative, inconclusive or insufficient results in ongoing or future clinical trials, the FDA requiring additional information or data, delays in the progress of ongoing clinical trials, safety concerns arising with respect to our products or product candidates and disputes with the third parties from whom we license our products or product candidate; and (vi) delays by the FDA. Additional factors that could cause actual results to differ materially from those projected or suggested in any forward-looking statements are described under the heading "Risk Factors" in the Company's Quarterly Report on Form 10-Q for the quarter ending September 30, 2006 and in other filings that we may make with the Securities and Exchange Commission from time to time.