03/20/2006

Schering-Plough and PTC Therapeutics Announce Collaboration for Development of PTC's Preclinical Hepatitis C Compounds

KENILWORTH, N.J., and SOUTH PLAINFIELD, N.J., March 20, 2006 – Schering-Plough Corporation (NYSE: SGP) and PTC Therapeutics, Inc. (PTC) today announced that they have entered into an exclusive collaboration and licensing agreement for the development of PTC’s preclinical compounds for the oral treatment of hepatitis C virus (HCV) infection and other viral diseases. PTC’s small molecules are designed to inhibit the HCV Internal Ribosome Entry Site (IRES) mediated production of viral proteins. The IRES is highly conserved among all HCV genotypes and is required for the expression of all viral proteins involved in replication of the hepatitis C virus.

PTC identified the compounds in its HCV program through the company’s proprietary Gene Expression Modulation by Small-molecules (GEMS) technology.

“The goal of this alliance is to develop new oral therapies to improve treatment for patients with hepatitis C, one of the most serious and common blood borne infections in the world,” said Catherine D. Strader, Ph.D., executive vice president, discovery research, Schering-Plough Research Institute. “Schering-Plough is continuing its leadership in hepatitis C through internal research programs and strategic collaborations with innovative companies such as PTC, with a focus on developing targeted viral inhibitors,” she said.

“We are delighted to enter into this collaboration with Schering-Plough, as our teams share a commitment to develop new HCV therapies that will benefit patients,” said Stuart Peltz, president & CEO of PTC Therapeutics. “Schering-Plough’s expertise in the research and development of antiviral therapies and its global hepatitis franchise affords PTC the opportunity to realize the full potential of our IRES inhibitors. This collaboration provides additional validation for the GEMS technology and nicely complements our strategy as we advance internally the development of our clinical programs.”

Under the terms of the agreement, PTC and Schering-Plough will conduct a joint research program, and Schering-Plough will be responsible for development and commercialization efforts worldwide. Schering-Plough will make an upfront payment to PTC of $12 million and provide funding for PTC’s research efforts. Additionally, PTC can earn milestone payments if specific development, regulatory and commercial goals are achieved. Total payments to PTC could exceed $200 million. Schering-Plough will receive exclusive worldwide commercialization rights for any approved products and pay PTC royalties on worldwide net sales.

PTC’s proprietary Gene Expression Modulation by Small-molecules (GEMS) technology exploits the regulatory mechanisms found in the untranslated regions of messenger RNA for the identification of small molecule drugs that can treat diseases by selectively increasing or decreasing the expression of key proteins.

Chronic hepatitis C is estimated to affect more than 10 million people in major world markets, including in Canada, Europe and the United States. It is a leading cause of chronic liver disease and one of the most common reasons for liver transplant.

PTC Therapeutics is a privately-held biopharmaceutical company focused on the discovery, development and commercialization of small-molecule drugs targeting post-transcriptional control mechanisms. Post-transcriptional control processes are the sequence of events in the cell that ultimately regulate the rate and timing of all protein production. PTC discovers and develops small-molecule drugs that alter these processes by selectively modulating how RNA is used to produce proteins. This approach enables PTC to advance its drug discovery programs rapidly from targets to preclinical and clinical drug candidates, building a pipeline across multiple therapeutic areas including genetic disorders, oncology and infectious diseases.

Schering-Plough is a global science-based health care company with leading prescription, consumer and animal health products. Through internal research and collaborations with partners, Schering-Plough discovers, develops, manufactures and markets advanced drug therapies to meet important medical needs. Schering-Plough’s vision is to earn the trust of the physicians, patients and customers served by its more than 32,000 people around the world. The company is based in Kenilworth, N.J., and its Web site is www.schering-plough.com.

SCHERING-PLOUGH DISCLOSURE NOTICE: The information in this press release includes certain “forward-looking statements” within the meaning of the Securities Litigation Reform Act of 1995, including statements relating to the company’s strategy and the potential development of and market for drugs that treat hepatitis C. Forward-looking statements relate to expectations or forecasts of future events. Schering-Plough does not assume the obligation to update any forward-looking statement. Many factors could cause actual results to differ materially from Schering-Plough’s forward-looking statements, including market forces, economic factors, product availability, patent and other intellectual property protection, current and future branded, generic or over-the-counter competition, the regulatory process, and any developments following regulatory approval, among other uncertainties. For further details about these and other factors that may impact the forward-looking statements, see Schering-Plough’s Securities and Exchange Commission filings, including Item 1A. Risk Factors in the Company’s 2005 10-K.