英文药名: Letairis(Ambrisentan Tablets) 中文药名: 安贝生坦片 生产厂家: Glaxo Smith Kline 药品介绍 Ambrisentan是由美国Myogen公司开发的一种内皮素受体拮抗剂（ERA）。2006年11月17目美国Gilead Science公司收购Myogen作为子公司，并获得ambrisentan的所有权。该药物于2007年6月15目获得美国FDA批准，商品名为Letairis，口服用于治疗肺动脉高血压，其片剂具有5mg和10mg两种规格。 HIGHLIGHTS OF PRESCRIBING INFORMATION These highlights do not include all the information needed to use LETAIRIS ® safely and effectively. See full prescribing information for LETAIRIS. Letairis (ambrisentan) tablets, for oral use Initial U.S. Approval: 2007 WARNING: EMBRYO-FETAL TOXICITY See full prescribing information for complete boxed warning. Do not administer Letairis to a pregnant female because it may cause fetal harm (4.1, 5.1, 8.1). Females of reproductive potential: Exclude pregnancy before the start of treatment, monthly during treatment, and 1 month after stopping treatment. Prevent pregnancy during treatment and for one month after stopping treatment by using acceptable methods of contraception (2.2, 8.6). For all female patients, Letairis is available only through a restricted program called the Letairis Risk Evaluation and Mitigation Strategy (REMS) (5.2). RECENT MAJOR CHANGES Indications and Usage 10/2015 Dosage and Administration 10/2015 Warnings and Precautions 10/2015 INDICATIONS AND USAGE Letairis is an endothelin receptor antagonist indicated for the treatment of pulmonary arterial hypertension (PAH) (WHO Group 1): To improve exercise ability and delay clinical worsening. In combination with tadalafil to reduce the risks of disease progression and hospitalization for worsening PAH, and to improve exercise ability. Studies establishing effectiveness included trials predominantly in patients with WHO Functional Class II–III symptoms and etiologies of idiopathic or heritable PAH (60%) or PAH associated with connective tissue diseases (34%) (1). DOSAGE AND ADMINISTRATION Initiate treatment at 5 mg once daily (2.1). May be started with tadalafil (2.1). Titrate at 4-week intervals as needed and tolerated (2.1). Do not split, crush, or chew tablets (2.1). DOSAGE FORMS AND STRENGTHS Tablet: 5 mg and 10 mg (3) CONTRAINDICATIONS Pregnancy (4.1) Idiopathic Pulmonary Fibrosis (4.2) WARNINGS AND PRECAUTIONS Fluid retention may require intervention (5.3). If patients develop acute pulmonary edema during initiation of therapy with Letairis, consider underlying pulmonary veno-occlusive disease and discontinue treatment if necessary (5.4). Decreases in sperm count have been observed in patients taking endothelin receptor antagonists (5.5). Decreases in hemoglobin have been observed within the first few weeks; measure hemoglobin at initiation, at 1 month, and periodically thereafter (5.6). ADVERSE REACTIONS Most common adverse reactions (>3% compared to placebo) are peripheral edema, nasal congestion, sinusitis, and flushing (6.1). When used in combination with tadalafil, most common adverse reactions (>5% compared with either monotherapy) are peripheral edema, headache, nasal congestion, cough, anemia, dyspepsia, and bronchitis (6.1). To report SUSPECTED ADVERSE REACTIONS, contact Gilead Sciences, Inc. at (1-800-445-3235, Option 3) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. DRUG INTERACTIONS Cyclosporine increases ambrisentan exposure; limit ambrisentan dose to 5 mg once daily (7). USE IN SPECIFIC POPULATIONS Breastfeeding: Choose Letairis or breastfeeding (8.3). Not recommended in patients with moderate or severe hepatic impairment (8.8). See 17 for PATIENT COUNSELING INFORMATION and Medication Guide. Revised: 10/2015 FULL PRESCRIBING INFORMATION: CONTENTS* 1 INDICATIONS AND USAGE Letairis is indicated for the treatment of pulmonary arterial hypertension (PAH) (WHO Group 1): To improve exercise ability and delay clinical worsening. In combination with tadalafil to reduce the risks of disease progression and hospitalization for worsening PAH, and to improve exercise ability [see Clinical Studies (14.2)]. Studies establishing effectiveness included predominantly patients with WHO Functional Class II–III symptoms and etiologies of idiopathic or heritable PAH (60%) or PAH associated with connective tissue diseases (34%). 2 DOSAGE AND ADMINISTRATION 2.1 Adult Dosage Initiate treatment at 5 mg once daily, with or without tadalafil 20 mg once daily. At 4-week intervals, either the dose of Letairis or tadalafil can be increased, as needed and tolerated, to Letairis 10 mg or tadalafil 40 mg. Do not split, crush, or chew tablets. 2.2 Pregnancy Testing in Females of Reproductive Potential Initiate treatment with Letairis in females of reproductive potential only after a negative pregnancy test. Obtain monthly pregnancy tests during treatment [see Use in Specific Populations (8.6)].  3 DOSAGE FORMS AND STRENGTHS 5 mg and 10 mg film-coated tablets for oral administration Each 5 mg tablet is square convex, pale pink, with "5" on one side and "GSI" on the other side. Each 10 mg tablet is oval convex, deep pink, with "10" on one side and "GSI" on the other side. 4 CONTRAINDICATIONS 4.1 Pregnancy Letairis may cause fetal harm when administered to a pregnant female. Letairis is contraindicated in females who are pregnant. Letairis was consistently shown to have teratogenic effects when administered to animals. 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 [see Warnings and Precautions (5.1, 5.2) and Use in Specific Populations (8.1)]. 4.2 Idiopathic Pulmonary Fibrosis Letairis is contraindicated in patients with Idiopathic Pulmonary Fibrosis (IPF), including IPF patients with pulmonary hypertension (WHO Group 3) [see Clinical Studies (14.4)]. 5 WARNINGS AND PRECAUTIONS 5.1 Embryo-fetal Toxicity Letairis may cause fetal harm when administered during pregnancy and is contraindicated for use in females who are pregnant. In females of reproductive potential, exclude pregnancy prior to initiation of therapy, ensure use of acceptable contraceptive methods, and obtain monthly pregnancy tests [see Dosage and Administration (2.2), and Use in Specific Populations (8.1, 8.6)]. Letairis is only available for females through a restricted program under a REMS [see Warnings and Precautions (5.2)]. 5.2 Letairis REMS Program For all females, Letairis is available only through a restricted program called the Letairis REMS, because of the risk of embryo-fetal toxicity [see Contraindications (4.1), Warnings and Precautions (5.1), and Use in Specific Populations (8.1, 8.6)]. Notable requirements of the Letairis REMS program include the following: Prescribers must be certified with the program by enrolling and completing training. All females, regardless of reproductive potential, must enroll in the Letairis REMS program prior to initiating Letairis. Male patients are not enrolled in the REMS. Females of reproductive potential must comply with the pregnancy testing and contraception requirements [see Use in Specific Populations (8.6)]. Pharmacies that dispense Letairis must be certified with the program and must dispense to female patients who are authorized to receive Letairis. Further information is available at www.letairisrems.com or 1-866-664-5327. 5.3 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 (6.1)]. Most edema was mild to moderate in severity. In addition, there have been postmarketing 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. Peripheral edema/fluid retention is more common with Letairis plus tadalafil than with Letairis or tadalafil alone. 5.4 Pulmonary Edema with Pulmonary Veno-occlusive Disease (PVOD) If patients develop acute pulmonary edema during initiation of therapy with vasodilating agents such as Letairis, the possibility of PVOD should be considered, and if confirmed Letairis should be discontinued. 5.5 Decreased Sperm Counts Decreased sperm counts have been observed in human and animal studies with another endothelin receptor antagonist and in animal fertility studies with ambrisentan. Letairis may have an adverse effect on spermatogenesis. Counsel patients about potential effects on fertility [see Use in Specific Populations (8.6) and Nonclinical Toxicology (13.1)]. 5.6 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. In the long-term open-label extension of the two pivotal clinical studies, mean decreases from baseline (ranging from 0.9 to 1.2 g/dL) in hemoglobin concentrations persisted for up to 4 years of treatment. There have been postmarketing reports of decreases in hemoglobin concentration and hematocrit that have resulted in anemia requiring transfusion. 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. 6 ADVERSE REACTIONS Clinically significant adverse reactions that appear in other sections of the labeling include: Embryo-fetal Toxicity [see Warnings and Precautions (5.1), Use in Specific Populations (8.1)] Fluid Retention [see Warnings and Precautions (5.3)] Pulmonary Edema with PVOD [see Warnings and Precautions (5.4)] Decreased Sperm Count [see Warnings and Precautions (5.5)] Hematologic Changes [see Warnings and Precautions (5.6)] 6.1 Clinical Trials Experience 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 are presented from two 12-week, placebo-controlled studies (ARIES-1 and ARIES-2) in patients with pulmonary arterial hypertension (PAH), and one randomized, double-blind, active-controlled trial in 605 patients with PAH (AMBITION) comparing Letairis plus tadalafil to Letairis or tadalafil alone. The exposure to Letairis in these studies ranged from 1 day to 4 years (N=357 for at least 6 months and N=279 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 reactions that occurred in >3% more patients receiving Letairis than receiving placebo are shown in Table 1. Table 1 Adverse Reactions with Placebo-Adjusted Rates >3% in ARIES-1 and ARIES-2  Placebo (N=132) Letairis (N=261) Adverse Reaction n (%) n (%) Placebo-adjusted (%) 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 Most adverse drug reactions were mild to moderate and only nasal congestion was dose-dependent. Few notable differences in the incidence of adverse 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 PAH during the clinical trials in patients with PAH 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 PAH during the clinical trials in patients with PAH 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. Combination Use with Tadalafil The mean exposure to Letairis + tadalafil in the AMBITION study was 78.7 weeks. The adverse reactions that occurred in >5% more patients receiving Letairis + tadalafil than receiving Letairis or tadalafil monotherapy in AMBITION are shown in Table 2. Table 2 Adverse Reactions Reported More Commonly (>5%) on Letairis + Tadalafil than on Letairis or Tadalafil Monotherapy (ITT) in AMBITION Adverse Reactions Letairis + Tadalafil Combination Therapy (N=302) n (%) Letairis Monotherapy (N=152) n (%) Tadalafil Monotherapy (N=151) n (%) Peripheral edema 135 (45%) 58 (38%) 43 (28%) Headache 125 (41%) 51 (34%) 53 (35%) Nasal congestion 58 (19%) 25 (16%) 17 (11%) Cough 53 (18%) 20 (13%) 24 (16%) Anemia 44 (15%) 11 (7%) 17 (11%) Dyspepsia 32 (11%) 5 (3%) 18 (12%) Bronchitis 31 (10%) 6 (4%) 13 (9%) Peripheral edema was more frequent on combination therapy; however, there was no notable difference observed in the incidence of peripheral edema in elderly patients (≥65 years) versus younger patients (<65 years) on combination therapy (44% vs. 45%) or Letairis monotherapy (37% vs. 39%) in AMBITION. Treatment discontinuations due to adverse events while on randomized treatment were similar across treatment groups: 16% for Letairis + tadalafil, 14% for Letairis alone, and 13% for tadalafil alone. 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. 6.2 Postmarketing Experience The following adverse reactions were identified during post-approval use of Letairis. Because these reactions were reported voluntarily from a population of uncertain size, it is not possible to estimate reliably the frequency or to establish a causal relationship to drug exposure: anemia requiring transfusion [see Warnings and Precautions (5.6)] heart failure (associated with fluid retention), symptomatic hypotension, and hypersensitivity (e.g., angioedema, rash). 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)]. 7 DRUG INTERACTIONS Multiple dose coadministration 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 coadministered with cyclosporine [see Clinical Pharmacology (12.3)]. 8 USE IN SPECIFIC POPULATIONS 8.1 Pregnancy Pregnancy Category X Risk Summary Letairis may cause fetal harm when administered to a pregnant woman and is contraindicated during pregnancy. Letairis was teratogenic in rats and rabbits at doses which resulted in exposures of 3.5 and 1.7 times, respectively, the human dose of 10 mg per day. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, advise the patient of the potential hazard to a fetus [see Contraindications (4.1), Warnings and Precautions (5.1)]. Animal Data Letairis was teratogenic at oral dosages of ≥15 mg/kg/day (AUC 51.7 h∙µg/mL) in rats and ≥7 mg/kg/day (24.7 h∙µg/mL) in rabbits; it was not studied at lower dosages. These dosages are of 3.5 and 1.7 times, respectively, the human dose of 10 mg per day (14.8 h∙µg/mL) based on AUC. 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. A preclinical study in rats has shown decreased survival of newborn pups (mid and high dosages) and effects on testicle size and fertility of pups (high dosage) following maternal treatment with ambrisentan from late gestation through weaning. The mid and high dosages were 51 ×, and 170 × (on a mg/m2 body surface area basis) the maximum oral human dose of 10 mg and an average adult body weight of 70 kg. These effects were absent at a maternal dosage 17 × the human dose based on mg/m2. 8.3 Nursing Mothers It is not known whether ambrisentan is present in human milk. Because many drugs are present in human milk and because of the potential for serious adverse reactions in nursing infants from Letairis, a decision should be made whether to discontinue nursing or discontinue Letairis, taking into account the importance of the drug to the mother. 8.4 Pediatric Use Safety and effectiveness of Letairis in pediatric patients have not been established. 8.5 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. 8.6 Females and Males of Reproductive Potential Pregnancy Testing Female patients of reproductive potential must have a negative pregnancy test prior to initiation of treatment, monthly pregnancy test during treatment, and 1 month after stopping treatment with Letairis. Advise patients to contact their healthcare provider if they become pregnant or suspect they may be pregnant. Perform a pregnancy test if pregnancy is suspected for any reason. For positive pregnancy tests, counsel patient on the potential risk to the fetus and patient options [see Boxed Warning and Dosage and Administration (2.2)]. Contraception Female patients of reproductive potential must use acceptable methods of contraception during treatment with Letairis and for 1 month after stopping treatment with Letairis. Patients may choose one highly effective form of contraception (intrauterine device (IUD), contraceptive implant, or tubal sterilization) or a combination of methods (hormone method with a barrier method or two barrier methods). If a partner's vasectomy is the chosen method of contraception, a hormone or barrier method must be used along with this method. Counsel patients on pregnancy planning and prevention, including emergency contraception, or designate counseling by another healthcare provider trained in contraceptive counseling [see Boxed Warning]. Infertility Males 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. Counsel patients about the potential effects on fertility [see Warnings and Precautions (5.5)]. 8.7 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. 8.8 Hepatic Impairment Pre-existing 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 might 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. Elevation of Liver Transaminases Other endothelin receptor antagonists (ERAs) have been associated with aminotransferase (AST, ALT) elevations, hepatotoxicity, and cases of liver failure [see Adverse Reactions (6.1, 6.2)]. In patients who develop hepatic impairment after Letairis initiation, the cause of liver injury should be fully investigated. Discontinue Letairis if elevations of liver aminotransferases are >5 × ULN or if elevations are accompanied by bilirubin >2 × ULN, or by signs or symptoms of liver dysfunction and other causes are excluded. 10 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. 11 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. 12 CLINICAL PHARMACOLOGY 12.1 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. 12.2 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. N-terminal pro-B-type natriuretic peptide (NT-proBNP) In AMBITION [see Clinical Studies (14.2)], the decrease in NT-proBNP in patients on Letairis plus tadalafil was observed early (Week 4) and was sustained, with a reduction of 63% on Letairis plus tadalafil, 50% on Letairis alone, and 41% on tadalafil alone at Week 24. 12.3 Pharmacokinetics The pharmacokinetics of ambrisentan (S-ambrisentan) in healthy subjects is 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 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)]. In vitro studies found ambrisentan to have little to no inhibition of human hepatic transporters. Ambrisentan demonstrated weak dose-dependent inhibition of OATP1B1, OATP1B3, and NTCP (IC50 of 47 µM, 45 µM, and approximately 100 µM, respectively) and no transporter-specific inhibition of BSEP, BRCP, P-gp, or MRP2. 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 coadministration 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 13 NONCLINICAL TOXICOLOGY 13.1 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. 14 CLINICAL STUDIES 14.1 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 3 and Figure 4. Table 3 Changes from Baseline in 6-Minute Walk Distance (meters) (ARIES-1 and ARIES-2) 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)   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 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  Figure 4 Mean Change in 6-Minute Walk Distance (ARIES-1 and ARIES-2) 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. 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. 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 4 and Figure 5. Table 4 Time to Clinical Worsening (ARIES-1 and ARIES-2)  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, Log-rank test – 0.030 – 0.005 Intention-to-treat population. Note: Patients may have had more than one reason for clinical worsening. Nominal p-values 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 (ARIES-1 and ARIES-2) Time from randomization to clinical worsening with Kaplan-Meier estimates of the proportions of patients without events 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. 14.2 Combination Treatment of PAH In a randomized, double-blind, active-controlled trial (AMBITION), 605 patients with WHO Functional Class II or III PAH were randomized 2:1:1 to once daily Letairis plus tadalafil or to Letairis or tadalafil alone. Treatment was initiated with Letairis 5 mg and tadalafil 20 mg. If tolerated, tadalafil was increased to 40 mg at 4 weeks and Letairis was increased to 10 mg at 8 weeks. The primary endpoint was time to first occurrence of (a) death, (b) hospitalization for worsening PAH, (c) >15% decrease from baseline in 6MWD combined with WHO Functional Class III or IV symptoms sustained over 14 days (short term clinical worsening), or (d) reduction in 6MWD sustained over 14 days combined with WHO Functional Class III or IV symptoms sustained over 6 months (inadequate long term clinical response). Patients had idiopathic PAH (55%), heritable PAH (3%), or PAH associated with connective tissue diseases, congenital heart disease, stable HIV infection, or drugs or toxins (APAH, 43%). Median time from diagnosis to first study drug administration was 25 days. Approximately 32% and 68% of patients were in WHO Functional Class II and III, respectively. The mean patient age was 55.7 years (34% were ≥65 years old). Most patients were white (90%) and female (76%); 45% were North American. Principal results are shown in Figures 6 and 7. Figure 6 Time to Primary Endpoint Event (AMBITION) Figure 7 Primary Endpoint Events and First Occurrences of Each Component at Any Time (AMBITION) The treatment effect of Letairis plus tadalafil compared with individual monotherapy on time to first primary endpoint event was consistent across subgroups. (Figure 8). Figure 8 Primary Endpoint by Subgroups (AMBITION) Note: The figure above presents effects in various subgroups all of which are baseline characteristics and all of which were pre-specified, if not the groupings. The 95% confidence limits that are shown do not take into account how many comparisons were made, nor do they reflect the effect of a particular factor after adjustment for all other factors. Apparent homogeneity or heterogeneity among groups should not be over interpreted. Exercise Ability Results of the 6MWD at 24 weeks for the AMBITION study are shown in Table 5 and Figure 9. Table 5 6-Minute Walk Distance at Week 24 (meters)* (AMBITION)  Letairis + Tadalafil (N=302) Letairis Monotherapy (N=152) Tadalafil Monotherapy (N=151)   Baseline (median) 356 366 352 Change from baseline (median) 43 23 22 Median difference from Letairis + Tadalafil (95% CI) 24 (11, 37) 20 (8, 32) P-Value 0.0004 0.0016 Missing values at Week 24 were imputed using Worst Rank scores for patients with an adjudicated clinical failure event of death or hospitalization, and Last Observed Carried Forward otherwise. Figure 9 Median Change in 6-Minute Walk Distance (meters) in AMBITION 14.3 Long-term Treatment of PAH In long-term follow-up of patients who were treated with Letairis (2.5 mg, 5 mg, or 10 mg once daily) in the two pivotal studies and their open-label extension (N=383), Kaplan-Meier estimates of survival at 1, 2, and 3 years were 93%, 85%, and 79%, respectively. Of the patients who remained on Letairis for up to 3 years, the majority received no other treatment for PAH. 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 on mortality. 14.4 Adverse Effects in Idiopathic Pulmonary Fibrosis (IPF) A randomized controlled study in patients with IPF, with or without pulmonary hypertension (WHO Group 3), compared Letairis (N=329) to placebo (N=163). The study was terminated after 34 weeks for lack of efficacy, and was found to demonstrate a greater risk of disease progression or death on Letairis. More patients taking Letairis died (8% vs. 4%), had a respiratory hospitalization (13% vs. 6%), and had a decrease in FVC/DLCO (17% vs. 12%) [see Contraindications (4.2)].  16 HOW SUPPLIED/STORAGE AND HANDLING Letairis film-coated tablets are supplied as follows: Tablet Strength Package Configuration NDC No. Description of Tablet; Debossed on Tablet; Size 5 mg 30 count blister 61958-0801-2 Square convex; pale pink; "5" on side 1 and "GSI" on side 2; 6.6 mm Square 30 count bottle 61958-0801-1 10 count blister 61958-0801-3 10 count bottle 61958-0801-5 10 mg 30 count blister 61958-0802-2 Oval convex; deep pink; "10" on side 1 and "GSI" on side 2; 9.8 mm × 4.9 mm Oval 30 count bottle 61958-0802-1 10 count blister 61958-0802-3 10 count bottle 61958-0802-5 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. 17 PATIENT COUNSELING INFORMATION Advise patients to read the FDA-approved patient labeling (Medication Guide) Embryo-fetal Toxicity Instruct patients on the risk of fetal harm when Letairis is used in pregnancy [see Warnings and Precautions (5.1) and Use in Specific Populations (8)]. Female patients must enroll in the Letairis REMS program. Instruct females of reproductive potential to immediately contact their physician if they suspect they may be pregnant. Letairis REMS Program For female patients, Letairis is only available through a restricted program called the Letairis REMS [see Contraindications (4.1), Warnings and Precautions (5.2)]. Male patients are not enrolled in the Letairis REMS. Inform female patients (and their guardians, if applicable) of the following notable requirements: All female patients must sign an enrollment form. Advise female patients of reproductive potential that they must comply with the pregnancy testing and contraception requirements [see Use in Specific Populations (8.6)]. Educate and counsel females of reproductive potential on the use of emergency contraception in the event of unprotected sex or known or suspected contraceptive failure. Advise pre-pubertal females to report any changes in their reproductive status immediately to their prescriber. Review the Letairis Medication Guide and REMS educational material with female patients. A limited number of pharmacies are certified to dispense Letairis. Therefore, provide patients with the telephone number and website for information on how to obtain the product. http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=725D4E73-6C83-477A-ADC6-0AE4A133A844 美国FDA批准Letairis联合他达拉非为治疗肺动脉高压新疗法 2015年10月29日，美国食品药品监督管理局（FDA）批准了Letairis® (安贝生坦)联合他达拉非用于治疗肺动脉高压（PAH）（WHO 1类），以减少恶化期肺动脉高压患者疾病进展及住院的风险，并提高运动能力。Letairis是一种内皮素受体拮抗剂，最初在2007年被美国批准用于肺动脉高压的单药治疗，以提升患者的运动能力并减缓临床恶化。他达拉非是PDE5抑制剂，于2009年起被美国批准用于肺动脉高压患者以提升运动能力。 “有充足的证据支持安贝生坦以及他达拉非治疗肺动脉高压的疗效，但关于将这两种药物早期联合应用于刚刚开始接受治疗的肺动脉高压患者是否可以降低未来疾病进展的问题一直存在，”加州大学洛杉矶分校大卫·格芬医学院的医学博士、教授，及Harbor-UCLA医学中心洛杉矶生物医学研究所肺动脉高压研究中心主管Ronald J. Oudiz说，“基于支持这项批准的数据，我们现在知道，比起分别应用这两种有效的单药治疗，早期开始接受Letairis及他达拉非联合应用的患者疾病进展及住院的可能性更小，并且运动能力也有更大提升。因此，对于患有肺动脉高压这一使人衰弱并威胁生命的疾病的患者来说，这项组合代表了一种新的治疗方案。” 支持这一项新标签的数据来自AMBITION研究（一项随机，双盲，多中心的研究，针对安贝生坦及他达拉非作为肺动脉高压患者的一线联合治疗方案）。在此研究中，605名WHO功能分级II或III的肺动脉高压患者随机（2:1:1）接受了不同方案，分别为每日一次Letairis联合他达拉非（n=302）、只有Letairis（n=152）或只有他达拉非（n=151）。Letairis的治疗起始量为5mg，他达拉非为20mg。如果发生耐受，则在第四周提升他达拉非至40mg，Letairis在第八周升至10mg。研究的主要终点是第一次发生以下事件的时间：死亡，因病情恶化而住院，WHO功能分级III或IV级持续14天以上（短期临床恶化）伴6分钟步行距离（6MWD）下降距基线超过15%，或WHO功能分级III或IV级持续6个月（不充分长期临床应答）伴6MWD下降超过14天以上。 在研究中，相较Letairis单药治疗组（风险比=0.51；95%置信区间：0.35,，0.73；p=0.0002）及他达拉非单药治疗组（风险比= 0.55，；95%置信区间0.37，0.81；p=0.002），Letairis联合他达拉非的联合治疗将发生以上主要终点的风险比分别降低了49%及45%。20%的联合治疗组患者经历了主要终点，而Letairis及他达拉非单药治疗组分别为35%及30%。 相较Letairis组（风险比=0.33；95%置信区间0.19，0.55）及他达拉非组（风险比= 0.44；95%置信区间0.25，0.79），联合治疗将恶化的肺动脉高压患者的住院率分别降低了67%及56%。总体上，8%的联合治疗组患者因疾病恶化住院，而其他两组分别为22%及15%。 在第24周的6MWD测试中，相较于Letairis组（95%置信区间11，37；p=0.0004）及他达拉非组（95%置信区间8，32；p=0.0016），接受联合治疗的患者6MWD也经历了统计学显著的提高，其差值中位数分别为24米及20米。  当联合应用Letairis及他达拉非时，常见的不良反应（比任意一项单药治疗>5%）有外周性水肿（联合组：45%；Letairis组：38%；他达拉非组：28%），头痛（联合组：41%；Letairis组：34%；他达拉非组：35%），鼻塞（联合组：19%；Letairis组：16%；他达拉非组：11%），咳嗽（联合组：18%；Letairis组：13%；他达拉非组：16%），贫血（联合组：15%；Letairis组：7%；他达拉非组：11%），消化不良（联合组：11%；Letairis组：3%；他达拉非组：12%）及支气管炎（联合组：10%；Letairis组：4%；他达拉非组：9%）。Letairis有说明书黑框警告以及关于胚胎-胎儿毒性的联合风险评估及缓和策略（REMS）项目；参看下列美国关于Letairis的重要安全信息。 AMBITION研究的数据被发表在新英格兰杂志中，而2015年8月发表于欧洲心脏杂志的“2015欧洲心脏病学会/欧洲呼吸学会关于肺动脉高压的诊断及治疗指南”中，Letairis联合他达拉非的方案成为了唯一被推荐用于肺动脉高压的起始联合治疗方案。 AMBITION研究由吉利德和葛兰素史克公司联合赞助。礼来制药也资助并供应了研究所用的他达拉非。吉利德在美国推广安贝生坦的商品名为Letairis，而葛兰素史克则在美国境外通过Volibris®来推广安贝生坦。 关于肺动脉高压（WHO 1类） 肺动脉高压是一种衰竭性疾病，其特征为肺部血管缩窄导致的肺动脉压力升高。肺动脉压力升高使心脏将血液泵至肺部氧合变得困难。肺动脉高压患者症状为气促，其心脏持续对抗高压最终导致患者因心力衰竭而死亡。肺动脉高压可能无任何潜在病因，也可能继发于其他疾病，例如结缔组织病、先天性心脏病、肝硬化及HIV感染。 关于Letairis Letairis的适应症为肺动脉高压（PAH）（WHO 1类），用以提升运动能力并减缓临床恶化。同时联合他达拉非来减少恶化性肺动脉高压的疾病进展及住院的风险，并提高运动能力。支持其有效性的研究主要包括以下患者：有WHO功能分级II-III级症状，特发性或遗传性肺动脉高压（60%），或肺动脉高压伴发结缔组织病（34%）。