Gilead Announces New Letairis®(Ambrisentan) Data for the Treatment ofPatients With Pulmonary Arterial Hypertension(WHO Group 1) With WHO Functional Class II orIII Symptoms

Gilead Sciences, Inc. (Nasdaq:GILD) today announced results of a

post-hoc analysis of data collected during the ARIES-1, ARIES-2 and

ARIES-E studies for Letairis® in pulmonary arterial hypertension (PAH) (WHO Group 1) patients with

primarily WHO functional class II or III symptoms. This analysis

compared one-year clinical outcomes for PAH (WHO Group 1) patients who

initially received placebo during the 12-week, placebo-controlled

ARIES-1 and ARIES-2 studies before receiving ambrisentan during a

long-term, open-label extension study (ARIES-E) to patients receiving

continuous ambrisentan treatment throughout the ARIES studies. Data from

this analysis were presented by Vallerie McLaughlin, MD, Associate

Professor of Medicine, Director, Pulmonary Hypertension Program at the

University of Michigan Health System, at ATS 2008 - Toronto, the International Conference of the American Thoracic Society

taking place May 16-21. Letairis (ambrisentan 5 mg and 10 mg tablets) is

indicated as a once-daily treatment for PAH (WHO Group 1) in patients

with WHO functional class II or III symptoms to improve exercise

capacity and delay clinical worsening. ARIES-1 and ARIES-2 were concurrent, double-blind, placebo-controlled

studies evaluating ambrisentan in PAH patients. The studies primarily

enrolled PAH patients with WHO functional class II or III symptoms.

These studies were identical in design except for the investigative

sites and doses of ambrisentan evaluated (ARIES-1: 5 or 10 mg; ARIES-2:

2.5 or 5 mg). In each study, patients were randomized to receive placebo

or ambrisentan orally once daily for 12 weeks. The primary endpoint for

each study was change in six-minute walk distance (6MWD) from baseline

to week 12. Following 12 weeks of treatment, patients continued

treatment with ambrisentan (ABS/ABS group, n=261) or crossed over from

treatment with placebo to ambrisentan (PLB/ABS group, n=132) in ARIES-E. In this analysis, one-year (48 weeks) clinical outcomes were examined

for patients in the ABS/ABS and the PLB/ABS groups. Baseline for all patients was defined as the time of randomization in

ARIES-1 or ARIES-2. Clinical efficacy measures assessed in this analysis

included 6MWD and time to clinical worsening. Clinical worsening was

defined as the time from randomization to the first occurrence of death

lung transplantation, hospitalization for PAH, arterial septostomy

study withdrawal due to the addition of other PAH therapeutics, or study

withdrawal due to two or more early escape criteria. A Kaplan-Meier

analysis was used to evaluate time to clinical worsening and includes

all patients from the time of randomization. Study Results Baseline characteristics were comparable between the ABS/ABS and PLB/ABS

groups. As previously reported, the change from baseline 6MWD at week 12

in the ambrisentan group was +42 meters (95 percent CI: 34 to 51)

compared to +3 meters in the placebo group (95 percent CI: -10 to 16).

At week 12 of treatment, 96 percent of patients in the ambrisentan group

(95 percent CI: 93 percent to 98 percent) were event-free, compared to

86 percent of patients in the placebo group (95 percent CI: 80 percent

to 92 percent). At week 48, 6MWD in the ABS/ABS group was +47 meters (95 percent CI: 35

to 59) compared to 33 meters in the PLB/ABS group (95 percent CI: 16 to

50). Following the addition of ambrisentan to the placebo group after

week 12, the rate of clinical worsening decreased for the PLB/ABS group.

At one year of treatment, the probability of no clinical worsening was

84 percent in the ABS/ABS group (95 percent CI: 80 percent to 89

percent) compared to 76 percent in the PLB/ABS group (95 percent CI: 68

percent to 83 percent). "Despite the availability of multiple

therapies, PAH is often not diagnosed in a timely manner, largely

because classic PAH symptoms such as shortness of breath and chest pain

can be attributed to more common medical conditions," said Dr. McLaughlin. "This data analysis

suggests that delay of initiation of an effective therapy like

ambrisentan may result in a decreased long-term improvement in exercise

capacity and an increased risk of disease progression for patients with

PAH, highlighting the importance of early diagnosis and treatment." During the first 12 weeks of treatment, three (2.3 percent) placebo

patients had liver aminotransferases (ALT or AST) elevations greater

than three times the upper limit of normal (ULN) compared to zero

patients in the ambrisentan group. After one year of treatment, a total

of four (3.0 percent) PLB/ABS patients and four (1.5 percent) ABS/ABS

patients had aminotransferase abnormalities greater than three times

ULN. Peripheral edema and headache occurred in greater than or equal to

10 percent of patients in both the ambrisentan and placebo groups during

the first 12 weeks. By week 48, the adverse events occurring in greater

than or equal to 10 percent of patients in both the ABS/ABS and PLB/ABS

groups were peripheral edema, headache, dizziness, dyspnea exacerbated

upper respiratory tract infection and arthralgia. In addition, cough

nasal congestion and palpitations occurred in greater than or equal to

10 percent of patients in the ABS/ABS group. Nausea was observed in

greater than or equal to 10 percent of patients in the PLB/ABS group.

Right ventricular failure was observed in greater than or equal to 10

percent of patients at week 12 in the placebo group and at week 48 in

the PLB/ABS group. Data from this analysis comparing the PLB/ABS and ABS/ABS groups during

open-label follow-up treatment at 48 weeks have not been reviewed by the

U.S. Food and Drug Administration. Full prescribing information for Letairis is available at www.gilead.com and at www.letairis.com/downloads/LETAIRIS_prescribing_information.pdf. WARNING: POTENTIAL LIVER INJURY Letairis can cause elevation of liver aminotransferases (ALT and AST) to

at least three times the upper limit of normal (ULN). Letairis treatment

was associated with aminotransferase elevations greater than three times

ULN in 0.8 percent of patients in 12-week trials and 2.8 percent of

patients including long-term open-label trials out to one year. One case

of aminotransferase elevations greater than three times ULN has been

accompanied by bilirubin elevations greater than two times ULN. Because

these changes are a marker for potentially serious liver injury, serum

aminotransferase levels (and bilirubin if aminotransferase levels are

elevated) must be measured prior to initiation of treatment and then

monthly. Elevations in aminotransferases require close attention. Letairis should

generally be avoided in patients with elevated aminotransferases greater

than three times ULN at baseline because monitoring liver injury may be

more difficult. If liver aminotransferase elevations are accompanied by

clinical symptoms of liver injury (such as nausea, vomiting, fever

abdominal pain, jaundice, or unusual lethargy or fatigue) or increases

in bilirubin greater than two times ULN, treatment should be stopped.

There is no experience with the re-introduction of Letairis in these

circumstances. CONTRAINDICATION: PREGNANCY Letairis is very likely to produce serious birth defects if used by

pregnant women, as this effect has been seen consistently when it is

administered to animals. Pregnancy must therefore be excluded before the

initiation of treatment with Letairis and prevented thereafter by the

use of at least two reliable methods of contraception unless the patient

is unable to become pregnant. Obtain monthly pregnancy tests. About the Letairis Education and

Access Program (LEAP) Because of the risks of liver injury and birth defects, Letairis is

available only through a special restricted distribution program called

the Letairis Education and Access Program (LEAP) by calling

1-866-664-LEAP (1-866-664-5327). Only prescribers and pharmacies

registered with LEAP are able to prescribe and distribute Letairis. In

addition, Letairis may be dispensed only to patients who are enrolled in

and meet all conditions of LEAP. Important Safety Information Decreases in hemoglobin concentration and hematocrit have followed

administration of other endothelin receptor antagonists and were

observed in clinical studies with Letairis. These decreases were

observed within the first few weeks of treatment with Letairis, and

stabilized thereafter. Peripheral edema is a known class effect of endothelin receptor

antagonists and is also a clinical consequence of PAH and worsening PAH.

In the placebo-controlled studies, there was an increased incidence of

peripheral edema in patients treated with doses of 5 or 10 mg of

Letairis compared to placebo. Most edema was mild to moderate in

severity. Peripheral edema was similar in younger patients (age less

than 65 years) receiving Letairis (14 percent; 29/205) or placebo (13

percent; 13/104), and was greater in elderly patients (age greater than

or equal to 65 years) receiving Letairis (29 percent; 16/56) compared to

placebo (4 percent, 1/28). The results of such subgroup analyses must be

interpreted cautiously. In addition, there have been post-marketing reports of fluid retention

in patients with pulmonary hypertension, occurring within weeks after

starting Letairis. Patients required intervention with a diuretic, fluid

management, or, in some cases, hospitalization for decompensating heart

failure. Because the post-marketing experience was reported voluntarily

from a population of uncertain size, it is not possible to reliably

estimate the relative frequency or establish a causal relationship to

Letairis drug exposure. Caution should be used when Letairis is co-administered with

cyclosporine A, as it may cause increased exposure to Letairis. Caution should be used when Letairis is co-administered with strong

CYP3A-inhibitors (e.g., ketoconazole) or CYP2C19-inhibitors (e.g.

omeprazole). The most common adverse events that occurred at a higher frequency among

Letairis-treated patients compared to placebo included (placebo-adjusted

frequency): peripheral edema (6 percent), nasal congestion (4 percent)

sinusitis (3 percent), flushing (3 percent), palpitations (3 percent)

nasal pharyngitis (2 percent), abdominal pain (2 percent), constipation

(2 percent), dyspnea (1 percent) and headache (1 percent). No clinically relevant interactions of Letairis with warfarin or

sildenafil have been observed. Letairis is not recommended in patients with moderate to severe hepatic

impairment. About Letairis Letairis (ambrisentan) is an endothelin receptor antagonist that has a

high affinity for the endothelin type-A (ETA) receptor. Activation of

the ETA receptor by endothelin-1 (ET-1), a small peptide hormone, leads

to vasoconstriction (narrowing of blood vessels) and cell proliferation.

The clinical impact of high selectivity for ETA is not known. Endothelin

concentrations are higher in the lung tissue of PAH patients, thus

suggesting that ET-1 may play a critical role in the pathogenesis or

progression of PAH. GlaxoSmithKline (GSK) holds rights to commercialize ambrisentan for PAH

in territories outside of the United States. On April 25, 2008, GSK

announced that the European Commission issued a marketing authorisation

for ambrisentan, under the tradename Volibris®

for the treatment of PAH in patients classified as WHO functional class

II and III, to improve exercise capacity. GSK has stated that its first

European launches of Volibris are planned in the summer of 2008. About Pulmonary Arterial Hypertension

(WHO Group 1) PAH is a debilitating disease characterized by constriction of the blood

vessels in the lungs leading to high pulmonary arterial pressures. These

high pressures make it difficult for the heart to pump blood through the

lungs to be oxygenated. Patients with PAH suffer from shortness of

breath as the heart struggles to pump against these high pressures

causing such patients to ultimately die of heart failure. PAH can occur

with no known underlying cause, or it can occur secondary to diseases

such as connective tissue disease, congenital heart defects, cirrhosis

of the liver and HIV infection. PAH afflicts approximately 200,000

patients worldwide. About Gilead Sciences Gilead Sciences is a biopharmaceutical company that discovers, develops

and commercializes innovative therapeutics in areas of unmet medical

need. The company´s mission is to advance the

care of patients suffering from life-threatening diseases worldwide.

Headquartered in Foster City, California, Gilead has operations in North

America, Europe and Australia. Letairis is a registered trademark of Gilead Sciences, Inc. Volibris is a registered trademark of Gilead Sciences, Inc. For more information on Gilead Sciences, please visit the company´s

website at www.gilead.com or call

Gilead Public Affairs at 1-800-GILEAD-5 or 1-650-574-3000.