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12 CLINICAL PHARMACOLOGY

12.1Mechanism of Action Salmeterol is a selective LABA. In vitro studies show salmeterol to be at least 50 times more selective for beta 2 -adrenoceptors than albuterol. Although beta 2 -adrenoceptors are the predominant adrenergic receptors in bronchial smooth muscle and beta 1 -adrenoceptors are the predominant receptors in the heart, there are also beta 2 -adrenoceptors in the human heart comprising 10% to 50% of the total beta-adrenoceptors.

The precise function of these receptors has not been established, but their presence raises the possibility that even selective beta 2 -agonists may have cardiac effects. The pharmacologic effects of beta 2 -adrenoceptor agonist drugs, including salmeterol, are at least in part attributable to stimulation of intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3′,5′-adenosine monophosphate (cyclic AMP). Increased cyclic AMP levels cause relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.

In vitro tests show that salmeterol is a potent and long-lasting inhibitor of the release of mast cell mediators, such as histamine, leukotrienes, and prostaglandin D 2 , from human lung. Salmeterol inhibits histamine-induced plasma protein extravasation and inhibits platelet-activating factor–induced eosinophil accumulation in the lungs of guinea pigs when administered by the inhaled route. In humans, single doses of salmeterol administered via inhalation aerosol attenuate allergen-induced bronchial hyper-responsiveness.

12.2Pharmacodynamics Inhaled salmeterol, like other beta-adrenergic agonist drugs, can produce dose-related cardiovascular effects and effects on blood glucose and/or serum potassium [see Warnings and Precautions ( 5.6 , 5.10 )] . The cardiovascular effects (heart rate, blood pressure) associated with salmeterol inhalation aerosol occur with similar frequency, and are of similar type and severity, as those noted following albuterol administration. The effects of rising inhaled doses of salmeterol and standard inhaled doses of albuterol were studied in volunteers and in subjects with asthma.

Salmeterol doses up to 84 mcg administered as inhalation aerosol resulted in heart rate increases of 3 to 16 beats/min, about the same as albuterol dosed at 180 mcg by inhalation aerosol (4 to 10 beats/min). Adult and adolescent subjects receiving 50-mcg doses of salmeterol inhalation powder (n = 60) underwent continuous electrocardiographic monitoring during two 12-hour periods after the first dose and after 1 month of therapy, and no clinically significant dysrhythmias were noted. Also, pediatric patients receiving 50-mcg doses of salmeterol inhalation powder (n = 67) underwent continuous electrocardiographic monitoring during two 12-hour periods after the first dose and after 3 months of therapy, and no clinically significant dysrhythmias were noted.

In 24-week clinical studies in patients with COPD, the incidence of clinically significant abnormalities on the predose ECGs at Weeks 12 and 24 in patients who received salmeterol 50 mcg was not different compared with placebo. No effect of treatment with salmeterol 50 mcg was observed on pulse rate and systolic and diastolic blood pressure in a subset of patients with COPD who underwent 12-hour serial vital sign measurements after the first dose (n = 91) and after 12 weeks of therapy (n = 74). Median changes from baseline in pulse rate and systolic and diastolic blood pressure were similar for patients receiving either salmeterol or placebo [see Adverse Reactions ( 6.1 )] .

Concomitant Use of SEREVENT DISKUS with Other Respiratory Medications Short-acting Beta 2 -agonists: In two 12-week repetitive-dose clinical trials in adult and adolescent subjects with asthma (N = 149), the mean daily need for additional beta 2 -agonist in subjects using SEREVENT DISKUS was approxim… [Excerpted — this section continues on DailyMed.]

12.1Mechanism of Action Salmeterol is a selective LABA. In vitro studies show salmeterol to be at least 50 times more selective for beta 2 -adrenoceptors than albuterol. Although beta 2 -adrenoceptors are the predominant adrenergic receptors in bronchial smooth muscle and beta 1 -adrenoceptors are the predominant receptors in the heart, there are also beta 2 -adrenoceptors in the human heart comprising 10% to 50% of the total beta-adrenoceptors.

The precise function of these receptors has not been established, but their presence raises the possibility that even selective beta 2 -agonists may have cardiac effects. The pharmacologic effects of beta 2 -adrenoceptor agonist drugs, including salmeterol, are at least in part attributable to stimulation of intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3′,5′-adenosine monophosphate (cyclic AMP). Increased cyclic AMP levels cause relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.

In vitro tests show that salmeterol is a potent and long-lasting inhibitor of the release of mast cell mediators, such as histamine, leukotrienes, and prostaglandin D 2 , from human lung. Salmeterol inhibits histamine-induced plasma protein extravasation and inhibits platelet-activating factor–induced eosinophil accumulation in the lungs of guinea pigs when administered by the inhaled route. In humans, single doses of salmeterol administered via inhalation aerosol attenuate allergen-induced bronchial hyper-responsiveness.

12.3Pharmacokinetics Salmeterol xinafoate, an ionic salt, dissociates in solution so that the salmeterol and 1-hydroxy-2-naphthoic acid (xinafoate) moieties are absorbed, distributed, metabolized, and eliminated independently. Salmeterol acts locally in the lung; therefore, plasma levels do not predict therapeutic effect. Absorption Because of the small therapeutic dose, systemic levels of salmeterol are low or undetectable after inhalation of recommended doses (50 mcg of salmeterol inhalation powder twice daily).

Following chronic administration of an inhaled dose of 50 mcg of salmeterol inhalation powder twice daily, salmeterol was detected in plasma within 5 to 45 minutes in 7 subjects with asthma; plasma concentrations were very low, with mean peak concentrations of 167 pg/mL at 20 minutes and no accumulation with repeated doses. Distribution The percentage of salmeterol bound to human plasma proteins averages 96% in vitro over the concentration range of 8 to 7,722 ng of salmeterol base per milliliter, much higher concentrations than those achieved following therapeutic doses of salmeterol.

Metabolism Salmeterol base is extensively metabolized by hydroxylation, with subsequent elimination predominantly in the feces. No significant amount of unchanged salmeterol base was detected in either urine or feces. An in vitro study using human liver microsomes showed that salmeterol is extensively metabolized to α-hydroxysalmeterol (aliphatic oxidation) by CYP3A4.

Ketoconazole, a strong inhibitor of CYP3A4, essentially completely inhibited the formation of α-hydroxysalmeterol in vitro. Elimination In 2 healthy adult subjects who received 1 mg of radiolabeled salmeterol (as salmeterol xinafoate) orally, approximately 25% and 60% of the radiolabeled salmeterol was eliminated in urine and feces, respectively, over a period of 7 days. The terminal elimination half-life was about 5.5 hours (1 volunteer only).

The xinafoate moiety has no apparent pharmacologic activity. The xinafoate moiety is highly protein bound (>99%) and has a long elimination half-life of 11 days. Drug Interaction Studies Inhibitors of Cytochrome P450 3A4: Ketoconazole: In a placebo-controlled crossover drug interaction trial in 20 healthy male and female subjects, coadministration of salmeterol (50 mcg twice daily) and the strong CYP3A4 inhibitor ketoconazole (400 mg once daily) for 7 days resulted in a significant increase in plasma salmeterol exposure as determined by a 16-fold increase in AUC (ratio with and without ketoconazole 15.76 [90% CI: 10.66, 23.31]) mainly due to increased bioavailability of the swallowed portion of the dose.

Peak plasma salmeterol concentrations were increased by 1.4-fold (90% CI: 1.23, 1.68). Three (3) out of 20 subjects (15%) were withdrawn from salmeterol and ketoconazole coadministration due to beta-agonist–mediated systemic effects (2 with QTc prolongation and 1 with palpitations and sinus tachycardia). Coadministration of salmeterol and ketoconazole did not result in a clinically significant effect on mean heart rate, mean blood potassium, or mean blood glucose.

Although there was no statistical effect on the mean QTc, coadministration of salmeterol and ketoconazole was associated with more frequent increases in QTc duration compared with salmeterol and placebo administration. Erythromycin: In a repeat-dose trial in 13 healthy subjects, concomitant administration of erythromycin (a moderate CYP3A4 inhibitor) and salmeterol inhalation aerosol resulted in a 40% increase in salmeterol C max at steady state (ratio with and without erythromycin 1.4 [90% CI: 0.96, 2.03], P = 0.12), a 3.6-beat/min increase in heart rate ([95% CI: 0.19, 7.03], P <0.04), a 5.8-msec increase in QTc interval ([95% CI: -6.14, 17.77], P = 0.34), and no change in plasma potassium.

12.2Pharmacodynamics Inhaled salmeterol, like other beta-adrenergic agonist drugs, can produce dose-related cardiovascular effects and effects on blood glucose and/or serum potassium [see Warnings and Precautions ( 5.6 , 5.10 )] . The cardiovascular effects (heart rate, blood pressure) associated with salmeterol inhalation aerosol occur with similar frequency, and are of similar type and severity, as those noted following albuterol administration. The effects of rising inhaled doses of salmeterol and standard inhaled doses of albuterol were studied in volunteers and in subjects with asthma.

Salmeterol doses up to 84 mcg administered as inhalation aerosol resulted in heart rate increases of 3 to 16 beats/min, about the same as albuterol dosed at 180 mcg by inhalation aerosol (4 to 10 beats/min). Adult and adolescent subjects receiving 50-mcg doses of salmeterol inhalation powder (n = 60) underwent continuous electrocardiographic monitoring during two 12-hour periods after the first dose and after 1 month of therapy, and no clinically significant dysrhythmias were noted. Also, pediatric patients receiving 50-mcg doses of salmeterol inhalation powder (n = 67) underwent continuous electrocardiographic monitoring during two 12-hour periods after the first dose and after 3 months of therapy, and no clinically significant dysrhythmias were noted.

In 24-week clinical studies in patients with COPD, the incidence of clinically significant abnormalities on the predose ECGs at Weeks 12 and 24 in patients who received salmeterol 50 mcg was not different compared with placebo. No effect of treatment with salmeterol 50 mcg was observed on pulse rate and systolic and diastolic blood pressure in a subset of patients with COPD who underwent 12-hour serial vital sign measurements after the first dose (n = 91) and after 12 weeks of therapy (n = 74). Median changes from baseline in pulse rate and systolic and diastolic blood pressure were similar for patients receiving either salmeterol or placebo [see Adverse Reactions ( 6.1 )] .

Concomitant Use of SEREVENT DISKUS with Other Respiratory Medications Short-acting Beta 2 -agonists: In two 12-week repetitive-dose clinical trials in adult and adolescent subjects with asthma (N = 149), the mean daily need for additional beta 2 -agonist in subjects using SEREVENT DISKUS was approximately 1½ inhalations/day. Twenty-six percent (26%) of the subjects in these trials used between 8 and 24 inhalations of short-acting beta-agonist per day on 1 or more occasions. Nine percent (9%) of the subjects in these trials averaged over 4 inhalations/day over the course of the 12-week trials.

No increase in frequency of cardiovascular events was observed among the 3 subjects who averaged 8 to 11 inhalations/day; however, the safety of concomitant use of more than 8 inhalations/day of short-acting beta 2 -agonist with SEREVENT DISKUS has not been established. In 29 subjects who experienced worsening of asthma while receiving SEREVENT DISKUS during these trials, albuterol therapy administered via either nebulizer or inhalation aerosol (1 dose in most cases) led to improvement in FEV 1 and no increase in occurrence of cardiovascular adverse events.

In 2 clinical trials in subjects with COPD, the mean daily need for additional beta 2 -agonist for subjects using SEREVENT DISKUS was approximately 4 inhalations/day. Twenty-four percent (24%) of subjects using SEREVENT DISKUS averaged 6 or more inhalations of albuterol per day over the course of the 24-week trials. No increase in frequency of cardiovascular adverse reactions was observed among subjects who averaged 6 or more inhalations per day.

Methylxanthines: The concurrent use of intravenously or orally administered methylxanthines (e.g., aminophylline, theophylline) by subjects receiving salmeterol has not been completely evaluated. In 1 clinical trial in subjects with asthma, 87 subjects receiving SEREVENT Inhalation Aerosol 42 mcg twice daily concurrently with a theophyl… [Excerpted — this section continues on DailyMed.]

14 CLINICAL STUDIES

14.1Asthma The initial trials supporting the approval of SEREVENT DISKUS for the treatment of asthma did not require the regular use of ICS. However, for the treatment of asthma, SEREVENT DISKUS is currently indicated only as concomitant therapy with an ICS [see Indications and Usage ( 1.1 )] . Adult and Adolescent Subjects Aged 12 Years and Older In 2 randomized double-blind trials, SEREVENT DISKUS was compared with albuterol inhalation aerosol and placebo in adolescent and adult subjects with mild-to-moderate asthma (protocol defined as 50% to 80% predicted FEV 1 , actual mean of 67.7% at baseline), including subjects who did and who did not receive concurrent ICS.

The efficacy of SEREVENT DISKUS was demonstrated over the 12-week period with no change in effectiveness over this time period (Figure 1). There were no gender- or age-related differences in safety or efficacy. No development of tachyphylaxis to the bronchodilator effect was noted in these trials.

FEV 1 measurements (mean change from baseline) from these two 12-week trials are shown in Figure 1 for both the first and last treatment days. Figure 1. Serial 12-Hour FEV 1 from Two 12-Week Clinical Trials in Subjects with Asthma First Treatment Day Last Treatment Day (Week 12) Table 4 shows the treatment effects seen during daily treatment with SEREVENT DISKUS for 12 weeks in adolescent and adult subjects with mild-to-moderate asthma.

Table 4. Daily Efficacy Measurements in Two 12-Week Clinical Trials (Combined Data) a Statistically superior to placebo and albuterol ( P <0.001). b Statistically superior to placebo ( P <0.001). Parameter Time SEREVENT DISKUS Albuterol Inhalation Aerosol Placebo No. of randomized subjects 149 148 152 Mean AM peak expiratory flow (L/min) Baseline 12 weeks 395 394 394 427 a 394 396 Mean % days with no asthma symptoms Baseline 12 weeks 13 12 14 33 21 20 Mean % nights with no awakenings Baseline 12 weeks 63 68 70 85 a 71 73 Rescue medications (mean no. of inhalations per day) Baseline 12 weeks 4.3 4.3 4.2 1.6 b 2.2

3.3Asthma exacerbations (%) 15 16 14 Maintenance of efficacy for periods up to 1 year has been documented. SEREVENT DISKUS and SEREVENT Inhalation Aerosol were compared with placebo in 2 additional randomized double-blind clinical trials in adolescent and adult subjects with mild-to-moderate asthma. SEREVENT DISKUS 50 mcg and SEREVENT Inhalation Aerosol 42 mcg, both administered twice daily, produced significant improvements in pulmonary function compared with placebo over the 12-week period.

While no statistically significant differences were observed between the active treatments for any of the efficacy assessments or safety evaluations performed, there were some efficacy measures on which the metered-dose inhaler appeared to provide better results. Similar findings were noted in 2 randomized, single-dose, crossover comparisons of SEREVENT DISKUS and SEREVENT Inhalation Aerosol for the prevention of EIB. Therefore, while SEREVENT DISKUS was comparable to SEREVENT Inhalation Aerosol in clinical trials in mild-to-moderate subjects with asthma, it should not be assumed that they will produce clinically equivalent outcomes in all subjects.

Subjects on Concomitant Inhaled Corticosteroids: In 4 clinical trials in adult and adolescent subjects with asthma (N = 1,922), the effect of adding SEREVENT Inhalation Aerosol to ICS therapy was evaluated over a 24-week treatment period. The trials compared the addition of salmeterol therapy to an increase (at least doubling) of the ICS dose. Two randomized, double-blind, controlled, parallel-group clinical trials (N = 997) enrolled subjects (aged 18 to 82 years) with persistent asthma who were previously maintained but not adequately controlled on ICS therapy.

During the 2-week run-in period, all subjects were switched to beclomethasone dipropionate (BDP) 168 mcg twice daily. Subjects still not adequately controlled were randomized to either the addition of SEREVENT Inhalat… [Excerpted — this section continues on DailyMed.]

13 NONCLINICAL TOXICOLOGY

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility In an 18-month carcinogenicity study in CD-mice, salmeterol at oral doses of 1,400 mcg/kg and above (approximately 20 times the MRHDID for adults and children based on comparison of the plasma AUCs) caused a dose-related increase in the incidence of smooth muscle hyperplasia, cystic glandular hyperplasia, leiomyomas of the uterus, and ovarian cysts. No tumors were seen at 200 mcg/kg (approximately 3 times the MRHDID for adults and children based on comparison of the AUCs).

In a 24-month oral and inhalation carcinogenicity study in Sprague Dawley rats, salmeterol caused a dose-related increase in the incidence of mesovarian leiomyomas and ovarian cysts at doses of 680 mcg/kg and above (approximately 66 and 35 times the MRHDID for adults and children, respectively, on a mcg/m 2 basis). No tumors were seen at 210 mcg/kg (approximately 20 and 10 times the MRHDID for adults and children, respectively, on a mcg/m 2 basis). These findings in rodents are similar to those reported previously for other beta-adrenergic agonist drugs.

The relevance of these findings to human use is unknown. Salmeterol produced no detectable or reproducible increases in microbial and mammalian gene mutation in vitro. No clastogenic activity occurred in vitro in human lymphocytes or in vivo in a rat micronucleus test.

Fertility and reproductive performance were unaffected in male and female rats at oral doses up to 2,000 mcg/kg (approximately 195 times the MRHDID for adults on a mcg/m 2 basis).

13.2Animal Toxicology and/or Pharmacology Preclinical Studies in laboratory animals (minipigs, rodents, and dogs) have demonstrated the occurrence of cardiac arrhythmias and sudden death (with histologic evidence of myocardial necrosis) when beta-agonists and methylxanthines are administered concurrently. The clinical relevance of these findings is unknown.