Press Release

Quebec City, April 29, 2005 --Today GlaxoSmithKline (GSK) presented new pharmacokinetic (PK) data on taking the HIV protease inhibitor LEXIVA(R) (fosamprenavir calcium, FPV) Tablets with the proton pump inhibitor (PPI), Nexium(R) (esomeprazole magnesium, ESO) 20mg Delayed-Release Capsules. When these agents were simultaneously co-administered there was no effect on amprenavir steady-state plasma levels. Current prescribing information in the U.S. for LEXIVA states that LEXIVA should be used with caution when co-administered with proton pump inhibitors as it may be less effective due to decreased amprenavir concentrations in patients taking these agents concomitantly. GSK performed an interaction study to determine if the simultaneous co-administration of esomeprazole alters the pharmacokinetics of LEXIVA. PPIs such as esomeprazole are potent inhibitors of the gastric acid pump and are often taken for the prevention and treatment of heartburn and other symptoms of gastroesophageal reflux disease (GERD). The study findings of APV10031, a randomized, open-label crossover study, were presented at the 6th International Workshop on Clinical Pharmacology of HIV Therapy in Quebec, Canada.

LEXIVA was co-discovered by GSK and Vertex Pharmaceuticals.

LEXIVA is indicated for the treatment of HIV infection in adults in combination with other antiretroviral medications. The following points should be considered when initiating therapy with LEXIVA plus ritonavir (RTV) (LEXIVA/r) in PI-experienced patients: the PI-experienced patient study was not large enough to reach a definitive conclusion that LEXIVA/r and lopinavir/ritonavir are clinically equivalent. Once-daily administration of LEXIVA plus RTV is not recommended for PI-experienced patients. LEXIVA is the first PI to offer flexible dosing options with no food or fluid restrictions.

"GERD is a common condition with up to 20 percent of the U.S. adult population reporting symptoms associated with chronic heartburn, and up to 40 percent of adults suffering from heartburn at least once a month. These data are important for healthcare professionals considering the use of this PPI for their patients taking antiretrovirals," commented Benjamin Young, M.D., and Ph.D., attending physician in infectious diseases at Rose Medical Center, Denver.

The APV10031 study was a crossover study in 48 healthy adult volunteers in the following three treatment periods:

• All subjects received 20mg of the PPI ESO once-a-day (QD) for seven days.
• Immediately thereafter, subjects received 20mg of ESO QD with either 1,400mg of LEXIVA twice-a-day (BID) or 700mg of LEXIVA plus 100mg of RTV BID for 14 days.
• Following a washout period of 21-28 days, subjects received 1400mg LEXIVA BID or 700mg of LEXIVA plus 100mg of RTV for 14 days.
• PK parameters from each combination of drugs were compared to each drug alone.

Based on the results, the authors concluded that simultaneous co-administration of 20mg ESO QD with either LEXIVA or LEXIVA/r had no effect on steady state plasma APV PK.

Specific results:
For all plasma APV parameters compared (AUC, Cmax, and Cmin), no significant differences were found when LEXIVA or LEXIVA/r were given simultaneously with ESO. ESO AUC and Cmax were unchanged when dosed in combination with LEXIVA/r, whereas ESO dosed in combination with LEXIVA increased ESO AUC by 55 percent and Cmax was unchanged, according to the study's authors.

Important Safety Information about LEXIVA
HIV medicines do not cure HIV infection/AIDS or prevent passing HIV to others.

LEXIVA is contraindicated in patients with previously demonstrated clinically significant hypersensitivity to any of the components of this product or to amprenavir. Hyperglycemia, new onset or exacerbations of diabetes mellitus and spontaneous bleeding in hemophiliacs have been reported with protease inhibitors.

LEXIVA is contraindicated with ergot derivatives, cisapride, pimozide, midazolam and triazolam. If LEXIVA is co-administered with ritonavir, flecainide and propafenone are also contraindicated. Treatment with LEXIVA/r has resulted in increases in the concentration of triglycerides. Triglyceride and cholesterol testing should be performed prior to initiating therapy with LEXIVA and at periodic intervals during therapy. The most common adverse events seen in clinical trials with LEXIVA were diarrhea, nausea, vomiting, headache and rash.

About Vertex
Vertex Pharmaceuticals Incorporated is a global biotechnology company committed to the discovery and development of breakthrough small molecule drugs for serious diseases. The Company's strategy is to commercialize its products both independently and in collaboration with major pharmaceutical companies. Vertex's product pipeline is principally focused on viral diseases, inflammation, autoimmune diseases and cancer. Vertex co-promotes the HIV protease inhibitor, LEXIVA with GlaxoSmithKline.

LEXIVA is a registered trademark of the GlaxoSmithKline group of companies.
Nexium(R) is a registered trademark of AstraZeneca group of companies.

Vertex Safe Harbor Statement
This press release may contain forward-looking statements. While management makes its best efforts to be accurate in making forward-looking statements, such statements are subject to risks and uncertainties that could cause Vertex's actual results to vary materially. These risks and uncertainties include those risks listed under Risk Factors in Vertex's Form 10-K filed with the Securities and Exchange Commission on March 16, 2005.

Vertex Contacts:
Lora Pike, Manager, Investor Relations, (617) 444-6755
Zachry Barber, Media Relations Specialist, (617) 444-6470

GlaxoSmithKline Contacts:
Mary Faye Dark, GSK, (919) 483-2839
Beth Schlesinger, Public Communications Inc., (312) 558-1770