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Letairis
ambrisentan
Dosage Form: tablet, film coated
FULL PRESCRIBING INFORMATION
WARNING: CONTRAINDICATED IN 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 [see Contraindications (4.1)]. Pregnancy must therefore be excluded before the initiation of treatment with Letairis and prevented during treatment 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.

Because of the risk of 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 (5327). Only prescribers and pharmacies registered with LEAP may prescribe and distribute Letairis. In addition, Letairis may be dispensed only to patients who are enrolled in and meet all conditions of LEAP [see Warnings and Precautions (5.1)].

Indications and Usage for Letairis

Letairis is indicated for the treatment of pulmonary arterial hypertension (PAH) (WHO Group 1) to improve exercise ability and delay clinical worsening. Studies establishing effectiveness included predominantly patients with WHO Functional Class II–III symptoms and etiologies of idiopathic or heritable PAH (64%) or PAH associated with connective tissue diseases (32%).

Letairis Dosage and Administration

Adult Dosage

Initiate treatment at 5 mg once daily with or without food, and consider increasing the dose to 10 mg once daily if 5 mg is tolerated.

Tablets may be administered with or without food. Tablets should not be split, crushed, or chewed. Doses higher than 10 mg once daily have not been studied in patients with pulmonary arterial hypertension (PAH).

Women of Childbearing Potential

Treat women of childbearing potential only after a negative pregnancy test and treat only women who are using 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. Pregnancy tests should be obtained monthly in women of childbearing potential taking Letairis [see Contraindications (4.1) and Warnings and Precautions (5.1)].

Pre-existing Hepatic Impairment

Letairis is not recommended in patients with moderate or severe hepatic impairment [see Use in Specific Populations (8.7)]. There is no information on the use of Letairis in patients with mild hepatic impairment; however, exposure to ambrisentan may be increased in these patients.

Dosage Forms and Strengths

Letairis is available as 5 mg and 10 mg film-coated, unscored tablets.

Contraindications

Pregnancy Category X

Letairis may cause fetal harm when administered to a pregnant woman. Ambrisentan was teratogenic at oral doses of ?15 mg/kg/day in rats and ?7 mg/kg/day in rabbits; it was not studied at lower doses. In both species, there were abnormalities of the lower jaw and hard and soft palate, malformation of the heart and great vessels, and failure of formation of the thymus and thyroid. Teratogenicity is a class effect of endothelin receptor antagonists. There are no data on the use of Letairis in pregnant women.

Letairis is contraindicated in women who are or may become pregnant. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to a fetus. Pregnancy must be excluded before the initiation of treatment with Letairis and prevented during treatment and for one month after stopping treatment by the use of two acceptable methods of contraception. If the patient has had a tubal sterilization or chooses to use a Copper T 380A IUD or LNg 20 IUS for pregnancy prevention, no additional contraception is needed [see Dosage and Administration (2.2), and Warnings and Precautions (5.1)].

Warnings and Precautions

Prescribing and Distribution Program for Letairis

 Because of the risk of birth defects, Letairis is available only through a special restricted distribution program called the Letairis Education and Access Program (LEAP). Only prescribers and pharmacies registered with LEAP may prescribe and distribute Letairis. In addition, Letairis may be dispensed only to patients who are enrolled in and meet all conditions of LEAP.

To enroll in LEAP, prescribers must complete the LEAP Prescriber Enrollment and Agreement Form indicating agreement to (see LEAP Prescriber Enrollment and Agreement Form for full prescribing physician agreement):

  • Read the Prescribing Information (PI) and Medication Guide for Letairis.
  • Enroll all patients in LEAP and re-enroll patients after the first 12 months of treatment and annually thereafter.
  • Review the Letairis Medication Guide and patient education brochure(s) with every patient.
  •  Educate patients on the risks of Letairis, including the risk of teratogenicity [see Boxed Warning, Warnings and Precautions (5), and Adverse Reactions (6)].
  • Educate and counsel women of childbearing potential to use highly reliable contraception during Letairis treatment and for one month after stopping treatment. If the patient has had a tubal sterilization or chooses to use a Copper T 380A IUD or LNg 20 IUS for pregnancy prevention, no additional contraception is needed. Women who do not choose one of these methods should always use two acceptable forms of contraception–one hormone method and one barrier method, or two barrier methods where one method is the male condom.
    • Acceptable hormone methods include: progesterone injectables, progesterone implants, combination oral contraceptives, transdermal patch, and vaginal ring.
    • Acceptable barrier methods include: diaphragm (with spermicide), cervical cap (with spermicide), and the male condom.
    • Partner's vasectomy must be used along with a hormone method or a barrier method.
    •  Educate and counsel women of childbearing potential on the use of emergency contraception in the event of unprotected sex or known or suspected contraceptive failure [see Boxed Warning, Contraindications (4.1)].
  • For women of childbearing potential, order and review a pregnancy test prior to initiation of Letairis treatment and monthly during treatment.
  •  Order and review tests for serum liver enzymes as clinically indicated since some members of this pharmacologic class are hepatotoxic.
  • Counsel patients who fail to comply with the program requirements.
  • Notify LEAP of any adverse events or if any patient becomes pregnant during Letairis treatment.

Fluid Retention

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 Letairis compared to placebo [see Adverse Reactions (6)]. Most edema was mild to moderate in severity, and it occurred with greater frequency and severity in elderly patients.

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.

If clinically significant fluid retention develops, with or without associated weight gain, further evaluation should be undertaken to determine the cause, such as Letairis or underlying heart failure, and the possible need for specific treatment or discontinuation of Letairis therapy.

Decreased Sperm Counts

In a 6-month study of another endothelin receptor antagonist, bosentan, 25 male patients with WHO functional class III and IV PAH and normal baseline sperm count were evaluated for effects on testicular function. There was a decline in sperm count of at least 50% in 25% of the patients after 3 or 6 months of treatment with bosentan. One patient developed marked oligospermia at 3 months and the sperm count remained low with 2 follow-up measurements over the subsequent 6 weeks. Bosentan was discontinued and after 2 months the sperm count had returned to baseline levels. In 22 patients who completed 6 months of treatment, sperm count remained within the normal range and no changes in sperm morphology, sperm motility, or hormone levels were observed. Based on these findings and preclinical data [see Nonclinical Toxicology (13.1)] from endothelin receptor antagonists, it cannot be excluded that endothelin receptor antagonists such as Letairis have an adverse effect on spermatogenesis.

Hematological Changes

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. The mean decrease in hemoglobin from baseline to end of treatment for those patients receiving Letairis in the 12-week placebo-controlled studies was 0.8 g/dL.

Marked decreases in hemoglobin (>15% decrease from baseline resulting in a value below the lower limit of normal) were observed in 7% of all patients receiving Letairis (and 10% of patients receiving 10 mg) compared to 4% of patients receiving placebo. The cause of the decrease in hemoglobin is unknown, but it does not appear to result from hemorrhage or hemolysis.

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. If a clinically significant decrease in hemoglobin is observed and other causes have been excluded, consider discontinuing Letairis.

Pulmonary Veno-occlusive Disease

 If patients develop acute pulmonary edema during initiation of therapy with vasodilating agents such as Letairis, the possibility of pulmonary veno-occlusive disease should be considered, and if confirmed Letairis should be discontinued.

Adverse Reactions

Clinical Trials Experience

See Warnings and Precautions (5.4) for discussion of hematological changes.

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Safety data for Letairis were obtained from two 12-week, placebo-controlled studies in patients with PAH (ARIES-1 and ARIES-2) and four nonplacebo-controlled studies in 483 patients with PAH who were treated with doses of 1, 2.5, 5, or 10 mg once daily. The exposure to Letairis in these studies ranged from 1 day to 4 years (N=418 for at least 6 months and N=343 for at least 1 year).

In ARIES-1 and ARIES-2, a total of 261 patients received Letairis at doses of 2.5, 5, or 10 mg once daily and 132 patients received placebo. The adverse events that occurred in >3% of the patients receiving Letairis and were more frequent on Letairis than placebo are shown in Table 1.

Table 1 Adverse Events in >3% of PAH Patients Receiving Letairis and More Frequent than Placebo
Placebo
(N=132)
Letairis
(N=261)
Adverse event n (%) n (%) Placebo-adjusted (%)
Note: This table includes all adverse events >3% incidence in the combined Letairis treatment group and more frequent than in the placebo group, with a difference of ?1% between the Letairis and placebo groups.
Peripheral edema 14 (11) 45 (17) 6
Nasal congestion 2 (2) 15 (6) 4
Sinusitis 0 (0) 8 (3) 3
Flushing 1 (1) 10 (4) 3
Palpitations 3 (2) 12 (5) 3
Nasopharyngitis 1 (1) 9 (3) 2
Abdominal pain 1 (1) 8 (3) 2
Constipation 2 (2) 10 (4) 2
Dyspnea 4 (3) 11 (4) 1
Headache 18 (14) 38 (15) 1

Most adverse drug reactions were mild to moderate and only nasal congestion was dose-dependent.

Few notable differences in the incidence of adverse drug reactions were observed for patients by age or sex. Peripheral edema was similar in younger patients (<65 years) receiving Letairis (14%; 29/205) or placebo (13%; 13/104), and was greater in elderly patients (?65 years) receiving Letairis (29%; 16/56) compared to placebo (4%; 1/28). The results of such subgroup analyses must be interpreted cautiously.

The incidence of treatment discontinuations due to adverse events other than those related to pulmonary hypertension during the clinical trials in patients with pulmonary arterial hypertension was similar for Letairis (2%; 5/261 patients) and placebo (2%; 3/132 patients). The incidence of patients with serious adverse events other than those related to pulmonary hypertension during the clinical trials in patients with pulmonary arterial hypertension was similar for placebo (7%; 9/132 patients) and for Letairis (5%; 13/261 patients).

During 12-week controlled clinical trials, the incidence of aminotransferase elevations >3 ? upper limit of normal (ULN) were 0% on Letairis and 2.3% on placebo. In practice, cases of hepatic injury should be carefully evaluated for cause.

Use in Patients with Prior Endothelin Receptor Antagonist (ERA) Related Serum Liver Enzyme Abnormalities

In an uncontrolled, open-label study, 36 patients who had previously discontinued endothelin receptor antagonists (ERAs: bosentan, an investigational drug, or both) due to aminotransferase elevations >3 ? ULN were treated with Letairis. Prior elevations were predominantly moderate, with 64% of the ALT elevations <5 ? ULN, but 9 patients had elevations >8 ? ULN. Eight patients had been re-challenged with bosentan and/or the investigational ERA and all eight had a recurrence of aminotransferase abnormalities that required discontinuation of ERA therapy. All patients had to have normal aminotransferase levels on entry to this study. Twenty-five of the 36 patients were also receiving prostanoid and/or phosphodiesterase type 5 (PDE5) inhibitor therapy. Two patients discontinued early (including one of the patients with a prior 8 ? ULN elevation). Of the remaining 34 patients, one patient experienced a mild aminotransferase elevation at 12 weeks on Letairis 5 mg that resolved with decreasing the dosage to 2.5 mg, and that did not recur with later escalations to 10 mg. With a median follow-up of 13 months and with 50% of patients increasing the dose of Letairis to 10 mg, no patients were discontinued for aminotransferase elevations. While the uncontrolled study design does not provide information about what would have occurred with re-administration of previously used ERAs or show that Letairis led to fewer aminotransferase elevations than would have been seen with those drugs, the study indicates that Letairis may be tried in patients who have experienced asymptomatic aminotransferase elevations on other ERAs after aminotransferase levels have returned to normal.

Postmarketing Experience

The following adverse reactions were identified during postapproval use of Letairis: Fluid retention [see Warnings and Precautions (5.2)], heart failure (associated with fluid retention), hypersensitivity (e.g., angioedema, rash), anemia, nausea, and vomiting.

Elevations of liver aminotransferases (ALT, AST) have been reported with Letairis use; in most cases alternative causes of the liver injury could be identified (heart failure, hepatic congestion, hepatitis, alcohol use, hepatotoxic medications). Other endothelin receptor antagonists have been associated with elevations of aminotransferases, hepatotoxicity, and cases of liver failure [see Adverse Reactions (6.1)]. Discontinue Letairis if >5? ULN or if elevations are accompanied by bilirubin >2? ULN, or by signs or symptoms of liver dysfunction and other causes are excluded.

Because these reactions were reported voluntarily from a population of uncertain size, it is not possible to reliably estimate the frequency or establish a causal relationship to drug exposure.

Drug Interactions

Multiple dose co-administration of ambrisentan and cyclosporine resulted in an approximately 2-fold increase in ambrisentan exposure in healthy volunteers; therefore, limit the dose of ambrisentan to 5 mg once daily when co-administered with cyclosporine [see Clinical Pharmacology (12.3)].

USE IN SPECIFIC POPULATIONS

Pregnancy

Pregnancy Category X [see Contraindications (4.1)].

Nursing Mothers

It is not known whether ambrisentan is excreted in human milk. Breastfeeding while receiving Letairis is not recommended. A preclinical study in rats has shown decreased survival of newborn pups (mid and high doses) and effects on testicle size and fertility of pups (high dose) following maternal treatment with ambrisentan from late gestation through weaning. Doses tested were 17?, 51?, and 170? (low, mid, high dose, respectively) the maximum oral human dose of 10 mg on a mg/mm2 basis.

Pediatric Use

Safety and effectiveness of Letairis in pediatric patients have not been established.

Geriatric Use

In the two placebo-controlled clinical studies of Letairis, 21% of patients were ?65 years old and 5% were ?75 years old. The elderly (age ?65 years) showed less improvement in walk distances with Letairis than younger patients did, but the results of such subgroup analyses must be interpreted cautiously. Peripheral edema was more common in the elderly than in younger patients.

Renal Impairment

The impact of renal impairment on the pharmacokinetics of ambrisentan has been examined using a population pharmacokinetic approach in PAH patients with creatinine clearances ranging between 20 and 150 mL/min. There was no significant impact of mild or moderate renal impairment on exposure to ambrisentan [see Clinical Pharmacology (12.3)]. Dose adjustment of Letairis in patients with mild or moderate renal impairment is therefore not required. There is no information on the exposure to ambrisentan in patients with severe renal impairment.

The impact of hemodialysis on the disposition of ambrisentan has not been investigated.

Hepatic Impairment

The influence of pre-existing hepatic impairment on the pharmacokinetics of ambrisentan has not been evaluated. Because there is in vitro and in vivo evidence of significant metabolic and biliary contribution to the elimination of ambrisentan, hepatic impairment would be expected to have significant effects on the pharmacokinetics of ambrisentan [see Clinical Pharmacology (12.3)]. Letairis is not recommended in patients with moderate or severe hepatic impairment. There is no information on the use of Letairis in patients with mild pre-existing impaired liver function; however, exposure to ambrisentan may be increased in these patients [see Dosage and Administration (2.3)].

Overdosage

There is no experience with overdosage of Letairis. The highest single dose of Letairis administered to healthy volunteers was 100 mg and the highest daily dose administered to patients with PAH was 10 mg once daily. In healthy volunteers, single doses of 50 mg and 100 mg (5 to 10 times the maximum recommended dose) were associated with headache, flushing, dizziness, nausea, and nasal congestion. Massive overdosage could potentially result in hypotension that may require intervention.

Letairis Description

Letairis is the brand name for ambrisentan, an endothelin receptor antagonist that is selective for the endothelin type-A (ETA) receptor. The chemical name of ambrisentan is (+)-(2S)-2-[(4,6-dimethylpyrimidin-2-yl)oxy]-3-methoxy-3,3-diphenylpropanoic acid. It has a molecular formula of C22H22N2O4 and a molecular weight of 378.42. It contains a single chiral center determined to be the (S) configuration and has the following structural formula:

Figure 1 Ambrisentan Structural Formula

Ambrisentan is a white to off-white, crystalline solid. It is a carboxylic acid with a pKa of 4.0. Ambrisentan is practically insoluble in water and in aqueous solutions at low pH. Solubility increases in aqueous solutions at higher pH. In the solid state ambrisentan is very stable, is not hygroscopic, and is not light sensitive.

Letairis is available as 5 mg and 10 mg film-coated tablets for once-daily oral administration. The tablets include the following inactive ingredients: croscarmellose sodium, lactose monohydrate, magnesium stearate and microcrystalline cellulose. The tablets are film-coated with a coating material containing FD&C Red #40 aluminum lake, lecithin, polyethylene glycol, polyvinyl alcohol, talc, and titanium dioxide. Each square, pale pink Letairis tablet contains 5 mg of ambrisentan. Each oval, deep pink Letairis tablet contains 10 mg of ambrisentan. Letairis tablets are unscored.

Letairis - Clinical Pharmacology

Mechanism of Action

Endothelin-1 (ET-1) is a potent autocrine and paracrine peptide. Two receptor subtypes, ETA and ETB, mediate the effects of ET-1 in the vascular smooth muscle and endothelium. The primary actions of ETA are vasoconstriction and cell proliferation, while the predominant actions of ETB are vasodilation, antiproliferation, and ET-1 clearance.

In patients with PAH, plasma ET-1 concentrations are increased as much as 10-fold and correlate with increased mean right atrial pressure and disease severity. ET-1 and ET-1 mRNA concentrations are increased as much as 9-fold in the lung tissue of patients with PAH, primarily in the endothelium of pulmonary arteries. These findings suggest that ET-1 may play a critical role in the pathogenesis and progression of PAH.

Ambrisentan is a high affinity (Ki=0.011 nM) ETA receptor antagonist with a high selectivity for the ETA versus ETB receptor (>4000-fold). The clinical impact of high selectivity for ETA is not known.

Pharmacodynamics

Cardiac Electrophysiology

In a randomized, positive- and placebo-controlled, parallel-group study, healthy subjects received either Letairis 10 mg daily followed by a single dose of 40 mg, placebo followed by a single dose of moxifloxacin 400 mg, or placebo alone. Letairis 10 mg daily had no significant effect on the QTc interval. The 40 mg dose of Letairis increased mean QTc at tmax by 5 ms with an upper 95% confidence limit of 9 ms. For patients receiving Letairis 5–10 mg daily and not taking metabolic inhibitors, no significant QT prolongation is expected.

Pharmacokinetics

The pharmacokinetics of ambrisentan (S-ambrisentan) in healthy subjects are dose proportional. The absolute bioavailability of ambrisentan is not known. Ambrisentan is absorbed with peak concentrations occurring approximately 2 hours after oral administration in healthy subjects and PAH patients. Food does not affect its bioavailability. In vitro studies indicate that ambrisentan is a substrate of P-gp. Ambrisentan is highly bound to plasma proteins (99%). The elimination of ambrisentan is predominantly by non-renal pathways, but the relative contributions of metabolism and biliary elimination have not been well characterized. In plasma, the AUC of 4-hydroxymethyl ambrisentan accounts for approximately 4% relative to parent ambrisentan AUC. The in vivo inversion of S-ambrisentan to R-ambrisentan is negligible. The mean oral clearance of ambrisentan is 38 mL/min and 19 mL/min in healthy subjects and in PAH patients, respectively. Although ambrisentan has a 15-hour terminal half-life, the mean trough concentration of ambrisentan at steady-state is about 15% of the mean peak concentration and the accumulation factor is about 1.2 after long-term daily dosing, indicating that the effective half-life of ambrisentan is about 9 hours.

Drug Interactions

In vitro studies

Studies with human liver tissue indicate that ambrisentan is metabolized by CYP3A, CYP2C19, and uridine 5'-diphosphate glucuronosyltransferases (UGTs) 1A9S, 2B7S, and 1A3S. In vitro studies suggest that ambrisentan is a substrate of the Organic Anion Transporting Polypeptides OATP1B1 and OATP1B3, and a substrate but not an inhibitor of P-glycoprotein (P-gp). Drug interactions might be expected because of these factors; however, a clinically relevant interaction has been demonstrated only with cyclosporine [see Drug Interactions (7)]. Ambrisentan does not inhibit or induce drug metabolizing enzymes at clinically relevant concentrations.

In vivo studies

The effects of other drugs on ambrisentan pharmacokinetics and the effects of ambrisentan on the exposure to other drugs are shown in Figure 2 and Figure 3, respectively.

Figure 2 Effects of Other Drugs on Ambrisentan Pharmacokinetics

* Omeprazole: based on population pharmacokinetic analysis in PAH patients

** Rifampin: AUC and Cmax were measured at steady-state. On Day 3 of co-administration a transient 2-fold increase in AUC was noted that was no longer evident by Day 7. Day 7 results are presented.

Figure 3 Effects of Ambrisentan on Other Drugs

* Active metabolite of mycophenolate mofetil

** GMR (95% CI) for INR

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

Oral carcinogenicity studies of up to two years duration were conducted at starting doses of 10, 30, and 60 mg/kg/day in rats (8 to 48 times the maximum recommended human dose [MRHD] on a mg/m2 basis) and at 50, 150 and 250 mg/kg/day in mice (28 to 140 times the MRHD). In the rat study, the high and mid-dose male and female groups had their doses lowered to 40 and 20 mg/kg/day, respectively, in week 51 because of effects on survival. The high dose males and females were taken off drug completely in weeks 69 and 93, respectively. The only evidence of ambrisentan-related carcinogenicity was a positive trend in male rats, for the combined incidence of benign basal cell tumor and basal cell carcinoma of skin/subcutis in the mid-dose group (high-dose group excluded from analysis), and the occurrence of mammary fibroadenomas in males in the high-dose group. In the mouse study, high dose male and female groups had their doses lowered to 150 mg/kg/day in week 39 and were taken off drug completely in week 96 (males) or week 76 (females). In mice, ambrisentan was not associated with excess tumors in any dosed group.

Positive findings of clastogenicity were detected, at drug concentrations producing moderate to high toxicity, in the chromosome aberration assay in cultured human lymphocytes. There was no evidence for genetic toxicity of ambrisentan when tested in vitro in bacteria (Ames test) or in vivo in rats (micronucleus assay, unscheduled DNA synthesis assay).

The development of testicular tubular atrophy and impaired fertility has been linked to the chronic administration of endothelin receptor antagonists in rodents. Testicular tubular degeneration was observed in rats treated with ambrisentan for two years at doses ?10 mg/kg/day (8-fold MRHD). Increased incidences of testicular findings were also observed in mice treated for two years at doses ?50 mg/kg/day (28-fold MRHD). Effects on sperm count, sperm morphology, mating performance and fertility were observed in fertility studies in which male rats were treated with ambrisentan at oral doses of 300 mg/kg/day (236-fold MRHD). At doses of ?10 mg/kg/day, observations of testicular histopathology in the absence of fertility and sperm effects were also present.

Clinical Studies

Pulmonary Arterial Hypertension (PAH)

Two 12-week, randomized, double-blind, placebo-controlled, multicenter studies were conducted in 393 patients with PAH (WHO Group 1). The two studies were identical in design except for the doses of Letairis and the geographic region of the investigational sites. ARIES-1 compared once-daily doses of 5 mg and 10 mg Letairis to placebo, while ARIES-2 compared once-daily doses of 2.5 mg and 5 mg Letairis to placebo. In both studies, Letairis or placebo was added to current therapy, which could have included a combination of anticoagulants, diuretics, calcium channel blockers, or digoxin, but not epoprostenol, treprostinil, iloprost, bosentan, or sildenafil. The primary study endpoint was 6-minute walk distance. In addition, clinical worsening, WHO functional class, dyspnea, and SF-36® Health Survey were assessed.

Patients had idiopathic or heritable PAH (64%) or PAH associated with connective tissue diseases (32%), HIV infection (3%), or anorexigen use (1%). There were no patients with PAH associated with congenital heart disease.

Patients had WHO functional class I (2%), II (38%), III (55%), or IV (5%) symptoms at baseline. The mean age of patients was 50 years, 79% of patients were female, and 77% were Caucasian.

Submaximal Exercise Ability

Results of the 6-minute walk distance at 12 weeks for the ARIES-1 and ARIES-2 studies are shown in Table 2 and Figure 4.

Table 2 Changes from Baseline in 6-Minute Walk Distance (meters)
ARIES-1 ARIES-2
Placebo
(N=67)
5 mg
(N=67)
10 mg
(N=67)
Placebo
(N=65)
2.5 mg
(N=64)
5 mg
(N=63)
Mean ± standard deviation
*
p-values are Wilcoxon rank sum test comparisons of Letairis to placebo at Week 12 stratified by idiopathic or heritable PAH and non-idiopathic, non-heritable PAH patients
Baseline 342 ± 73 340 ± 77 342 ± 78 343 ± 86 347 ± 84 355 ± 84
Mean change from baseline -8 ± 79 23 ± 83 44 ± 63 -10 ± 94 22 ± 83 49 ± 75
Placebo-adjusted mean change from baseline 31 51 32 59
Placebo-adjusted median change from baseline 27 39 30 45
p-value* 0.008 <0.001 0.022 <0.001
Figure 4 Mean Change in 6-Minute Walk Distance
Mean change from baseline in 6-minute walk distance in the placebo and Letairis groups
Values are expressed as mean ± standard error of the mean.
ARIES-1
ARIES-2

In both studies, treatment with Letairis resulted in a significant improvement in 6-minute walk distance for each dose of Letairis and the improvements increased with dose. An increase in 6-minute walk distance was observed after 4 weeks of treatment with Letairis, with a dose-response observed after 12 weeks of treatment. Improvements in walk distance with Letairis were smaller for elderly patients (age ?65) than younger patients and for patients with secondary PAH than for patients with idiopathic or heritable PAH. The results of such subgroup analyses must be interpreted cautiously.

The effects of Letairis on walk distances at trough drug levels are not known. Because only once daily dosing was studied in the clinical trials, the efficacy and safety of more frequent dosing regimens for Letairis are not known. If exercise ability is not sustained throughout the day in a patient, consider other PAH treatments that have been studied with more frequent dosing regimens.

Clinical Worsening

Time to clinical worsening of PAH was defined as the first occurrence of death, lung transplantation, hospitalization for PAH, atrial septostomy, study withdrawal due to the addition of other PAH therapeutic agents or study withdrawal due to early escape. Early escape was defined as meeting two or more of the following criteria: a 20% decrease in the 6-minute walk distance; an increase in WHO functional class; worsening right ventricular failure; rapidly progressing cardiogenic, hepatic, or renal failure; or refractory systolic hypotension. The clinical worsening events during the 12-week treatment period of the Letairis clinical trials are shown in Table 3 and Figure 5.

Table 3 Time to Clinical Worsening
ARIES-1 ARIES-2
Placebo
(N=67)
Letairis
(N=134)
Placebo
(N=65)
Letairis
(N=127)
Intention-to-treat population
Note: Patients may have had more than one reason for clinical worsening.
Nominal p-values
Clinical worsening, no. (%) 7 (10%) 4 (3%) 13 (22%) 8 (6%)
Hazard ratio 0.28 0.30
p-value, Fisher exact test 0.044 0.006
p-value, Log-rank test 0.030 0.005

There was a significant delay in the time to clinical worsening for patients receiving Letairis compared to placebo. Results in subgroups such as the elderly were also favorable.

Figure 5 Time to Clinical Worsening
Time from randomization to clinical worsening with Kaplan-Meier estimates of the proportions of failures in ARIES-1 and ARIES-2.
p-values shown are the log-rank comparisons of Letairis to placebo stratified by idiopathic or heritable PAH and non-idiopathic, non-heritable PAH patients
ARIES-1
ARIES-2

Long-term Treatment of PAH

The long-term follow-up of the patients who were treated with Letairis in the two pivotal studies and their open-label extension (N=383) shows that 95% were still alive at one year and 94% were still receiving Letairis monotherapy. These uncontrolled observations do not allow comparison with a group not given Letairis and cannot be used to determine the long-term effect of Letairis.

How Supplied/Storage and Handling

Letairis may be prescribed only through the Letairis Education and Access Program (LEAP) by calling 1-866-664-LEAP (5327) or by logging on to www.Letairis.com. Adverse events can also be reported directly via this number.

Letairis film-coated, unscored tablets are supplied as follows:

Package Configuration Tablet Strength NDC No. Description of Tablet;
Debossed on Tablet;
Size
30 count blister 5 mg 61958-0801-2 Square convex; pale pink;
"5" on side 1 and
"GSI" on side 2;
6.6 mm Square
30 count blister 10 mg 61958-0802-2 Oval convex; deep pink;
"10" on side 1 and
"GSI" on side 2;
9.8 mm ? 4.9 mm Oval

Rx only

Store at 25 °C (77 °F); excursions permitted to 15–30 °C (59–86 °F) [see USP controlled room temperature]. Store Letairis in its original packaging.

Patient Counseling Information

As a part of patient counseling, doctors must review the Letairis Medication Guide with every patient [see FDA-Approved Medication Guide (17.5)].

Importance of Preventing Pregnancy

Patients should be advised that Letairis may cause fetal harm. Letairis treatment should only be initiated in women of childbearing potential following a negative pregnancy test.

Women of childbearing potential should be informed of the importance of monthly pregnancy tests and the need to use highly reliable contraception during Letairis treatment and for one month after stopping treatment. If the patient has had a tubal sterilization or chooses to use a Copper T 380A IUD or LNg 20 IUS for pregnancy prevention, no additional contraception is needed. Women who do not choose one of these methods should always use two acceptable forms of contraception–one hormone method and one barrier method, or two barrier methods where one method is the male condom. Acceptable hormone methods include: progesterone injectables, progesterone implants, combination oral contraceptives, transdermal patch, and vaginal ring. Acceptable barrier methods include: diaphragm (with spermicide), cervical cap (with spermicide), and the male condom. Partner's vasectomy must be used along with a hormone method or a barrier method.

Patients should be instructed to immediately contact their physician if they suspect they may be pregnant. Educate and counsel women of childbearing potential on use of emergency contraception for patients whom have had unprotected sex or known or suspected contraceptive failure [see Warnings and Precautions (5.1)].

Hepatic Effects

Some members of this pharmacological class are hepatotoxic. Patients should be educated on the symptoms of potential liver injury (such as anorexia, nausea, vomiting, fever, malaise, fatigue, right upper quadrant abdominal discomfort, jaundice, dark urine or itching) and instructed to report any of these symptoms to their physician.

Hematological Change

Patients should be advised of the importance of hemoglobin testing.

Administration

Patients should be advised not to split, crush, or chew tablets.

FDA-Approved Medication Guide

*Sections or subsections omitted from the full prescribing information are not listed.

Gilead Sciences, Inc., Foster City, CA 94404

Revised July 2011

Letairis is a registered trademark of Gilead Sciences, Inc. Gilead and the Gilead logo are trademarks of Gilead Sciences, Inc. Other brands noted herein are the property of their respective owners.

© 2011 Gilead Sciences, Inc.

GS22-081-008

Medication Guide
Letairis® (le-TAIR-is)
(ambrisentan)
Tablets

Read this Medication Guide before you start taking Letairis and each time you get a refill. There may be new information. This Medication Guide does not take the place of talking with your doctor about your medical condition or your treatment.

What is the most important information I should know about Letairis?

  • Serious birth defects.
    Letairis can cause serious birth defects if taken during pregnancy. Women must not be pregnant when they start taking Letairis or become pregnant during treatment. Women who are able to get pregnant must have a negative pregnancy test before beginning treatment with Letairis and each month during treatment. Your doctor will decide when to do the test, depending on your menstrual cycle.
    Women who are able to get pregnant must use two acceptable forms of birth control, during Letairis treatment and for one month after stopping Letairis. If you have had a tubal sterilization or have an IUD, these methods can be used alone and no other form of birth control is needed. Talk with your doctor or gynecologist (a doctor who specializes in female reproduction) to find out about how to prevent pregnancy. Do not have unprotected sex. Talk to your doctor or pharmacist right away if you have unprotected sex or if you think your birth control has failed. Tell your doctor right away if you miss a menstrual period or think you may be pregnant.





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