November 02, 2009
Gilead Sciences Announces Plans for Phase IV Clinical Trial Evaluating First-Line Combination Therapy Versus Monotherapy in Pulmonary Arterial Hypertension
“The question of first-line combination therapy versus monotherapy is
one of the most important outstanding clinical questions in PAH,” said
AMBITION will be a double-blind, multicenter study, in which more than 300 treatment-naive PAH patients will be randomized to receive either the combination of ambrisentan and tadalafil or monotherapy (ambrisentan or tadalafil). Gilead and GSK are working with regulatory agencies and the PAH research community to finalize details of the study and plan to begin enrollment in 2010.
Full prescribing information for Letairis is available at www.gilead.com and at http://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.
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 and for one month after stopping treatment by the use of two acceptable methods of contraception unless the patient has had a tubal sterilization or chooses to use a Copper T 380A IUD or LNg 20 IUS, in which case no additional contraception is needed. 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. Physicians should measure hemoglobin prior to initiation of Letairis, at one month, and periodically thereafter. Initiation of Letairis therapy is not recommended for patients with clinically significant anemia.
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.
Decreases in sperm count have been observed in patients taking endothelin receptor antagonists.
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, sildenafil, tadalafil, omeprazole (CYP2C19 inhibitor), ketoconazole (strong CYP3A-inhibitor), digoxin, ethinylestradiol or norethindrone have been observed.
Other potential interactions are not well characterized, but, based on in vitro data, interactions with P-glycoprotein (P-gp), the Organic Anion Transport Protein (OATP), and uridine 5′-diphosphate glucuronosyltransferases (UGTs) would be expected.
Letairis is not recommended in patients with moderate to severe hepatic impairment.
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.
About Pulmonary Arterial Hypertension
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.
This press release includes forward-looking statements, within the
meaning of the Private Securities Litigation Reform Act of 1995, that
are subject to risks, uncertainties and other factors, including the
risks that Gilead and GSK may face challenges in the clinical trial
protocol design and may be unable to enroll patients in the trial in
2010 as currently anticipated. In addition, the results from the
clinical trial may be unfavorable, including showing no advantages from
combination therapy resulting from use of ambrisentan with tadalafil.
These risks, uncertainties and other factors could cause actual results
to differ materially from those referred to in the forward-looking
statements. The reader is cautioned not to rely on these forward-looking
statements. These and other risks are described in detail in Gilead’s
Quarterly Report on Form 10-Q for the second quarter of 2009, as filed
Letairis is a registered trademark of
For more information on
Gilead Sciences, Inc.
Susan Hubbard, Investors, 650-522-5715
Nathan Kaiser, Media, 650-522-1853