Montelukast Sodium

1 INDICATIONS AND USAGE Montelukast sodium chewable tablets are a leukotriene receptor antagonist indicated for: • Prophylaxis and chronic treatment of asthma in patients 2 years of age and older ( 1.1 ). • Acute prevention of exercise-induced bronchoconstriction (EIB) in patients 6 years of age and older ( 1.2 ). • Relief of symptoms of allergic rhinitis (AR): seasonal allergic rhinitis (SAR) in patients 2 years of age and older, and perennial allergic rhinitis (PAR) in patients 2 years of age and older. Reserve use for patients who have an inadequate response or intolerance to alternative therapies ( 1.3 ). 1.1 Asthma Montelukast sodium chewable tablets are indicated for the prophylaxis and chronic treatment of asthma in adults and pediatric patients 2 years of age and older. 1.2 Exercise-Induced Bronchoconstriction (EIB) Montelukast sodium chewable tablets are indicated for prevention of exercise-induced bronchoconstriction (EIB) in patients 6 years of age and older. 1.3 Allergic Rhinitis sodium chewable tablets are indicated for the relief of symptoms of seasonal allergic rhinitis in patients 2 years of age and older and perennial allergic rhinitis in patients 2 of age and older. Because the benefits of montelukast sodium chewable tablets may not outweigh the risk of neuropsychiatric symptoms in patients with allergic rhinitis , use for patients who have an inadequate response or intolerance to alternative therapies. Montelukast sodium chewable tablets are indicated for the relief of symptoms of seasonal allergic rhinitis in patients 2 years of age and older and perennial allergic rhinitis in patients 2 years of age and older. Because the benefits of montelukast sodium chewable tablets may not outweigh the risk of neuropsychiatric symptoms in patients with allergic rhinitis [see warnings and precautions ( 5.1 )] , reserve use for patients who have an inadequate response or intolerance to alternative therapies.

2 DOSAGE AND ADMINISTRATION Administration (by indications): • Asthma ( 2.1 ): Once daily in the evening for patients 2 years and older. • Acute prevention of EIB ( 2.2 ): One tablet at least 2 hours before exercise for patients 6 years of age and older. • Seasonal allergic rhinitis ( 2.3 ): Once daily for patients 2 years and older. • Perennial allergic rhinitis ( 2.3 ): Once daily for patients 2 years and older. Dosage (by age) ( 2 ): • 15 years and older: one 10-mg tablet. • 6 to 14 years: one 5-mg chewable tablet. • 2 to 5 years: one 4-mg chewable tablet. Patients with both asthma and allergic rhinitis should take only one dose daily in the evening ( 2.4 ). 2.1 Asthma Montelukast sodium should be taken once daily in the evening. The following doses are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. Safety and effectiveness in pediatric patients less than 12 months of age with asthma have not been established. who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time. There have been no clinical trials in patients with asthma to evaluate the relative efficacy of morning versus evening dosing. The pharmacokinetics of montelukast are similar whether dosed in the morning or evening. Efficacy has been demonstrated for asthma when montelukast was administered in the evening without regard to time of food ingestion. Montelukast sodium should be taken once daily in the evening. The following doses are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. Safety and effectiveness in pediatric patients less than 12 months of age with asthma have not been established. Patients who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time. There have been no clinical trials in patients with asthma to evaluate the relative efficacy of morning versus evening dosing. The pharmacokinetics of montelukast are similar whether dosed in the morning or evening. Efficacy has been demonstrated for asthma when montelukast was administered in the evening without regard to time of food ingestion. 2.2 Exercise-lnduced Bronchoconstriction (EIB) For prevention of EIB, a single dose of montelukast sodium should be taken at least 2 hours before exercise. The following doses are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. An additional dose of montelukast sodium should not be taken within 24 hours of a previous dose. Patients already taking montelukast sodium daily for another indication (including chronic asthma) should not take an additional dose to prevent EIB. All patients should have available for rescue a short-acting β-agonist. Safety and efficacy in patients younger than 6 years of age have not been established. Daily administration of montelukast sodium for the chronic treatment of asthma has not been established to prevent acute episodes of EIB. 2.3 Allergic Rhinitis For allergic rhinitis, montelukast sodium should be taken once daily. Efficacy was demonstrated for seasonal allergic rhinitis when montelukast was administered in the morning or the evening without regard to time of food ingestion. The time of administration may be individualized to suit patient needs. The following doses for the treatment of symptoms of seasonal allergic rhinitis are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. Safety and effectiveness in pediatric patients younger than 2 years of age with seasonal allergic rhinitis have not been established. The following doses for the treatment of symptoms of perennial allergic rhinitis are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. For allergic rhinitis, montelukast sodium should be taken once daily. Efficacy was demonstrated for seasonal allergic rhinitis when montelukast was administered in the morning or the evening without regard to time of food ingestion. The time of administration may be individualized to suit patient needs. The following doses for the treatment of symptoms of seasonal allergic rhinitis are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. Safety and effectiveness in pediatric patients younger than 2 years of age with seasonal allergic rhinitis have not been established. The following doses for the treatment of symptoms of perennial allergic rhinitis are recommended: For adults and adolescents 15 years of age and older: one 10-mg tablet. For pediatric patients 6 to 14 years of age: one 5-mg chewable tablet. For pediatric patients 2 to 5 years of age: one 4-mg chewable tablet. Safety and effectiveness in pediatric patients younger than 6 months of age with perennial allergic rhinitis have not been established. who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time. Safety and effectiveness in pediatric patients younger than 6 months of age with perennial allergic rhinitis have not been established. Patients who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time. 2.4 Asthma and Allergic Rhinitis Patients with both asthma and allergic rhinitis should take only one montelukast sodium dose daily in the evening. Patients with both asthma and allergic rhinitis should take only one montelukast sodium dose daily in the evening. who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time. Patients who miss a dose should take the next dose at their regular time and should not take 2 doses at the same time.

6 ADVERSE REACTIONS Most common adverse reactions (incidence ≥5% and greater than placebo listed in descending order of frequency): upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Hetero Labs Limited at 1-866-495-1995 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . See 17 for PATIENT COUNSELING INFORMATION and Medication Guide. Revised: 05/2020 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 clinical practice. In the following description of clinical trials experience, adverse reactions are listed regardless of causality assessment. The most common adverse reactions (incidence ≥5% and greater than placebo; listed in descending order of frequency) in controlled clinical trials were: upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis. Adults and Adolescents 15 Years of Age and Older with Asthma Montelukast sodium has been evaluated for safety in approximately 2950 adult and adolescent patients 15 years of age and older in clinical trials. In placebo-controlled clinical trials, the following adverse experiences reported with montelukast sodium occurred in greater than or equal to 1% of patients and at an incidence greater than that in patients treated with placebo: Table 1: Adverse Experiences Occurring in ≥1% of Patients with an Incidence Greater than that in Patients Treated with Placebo Montelukast Sodium 10 mg/day Placebo (%) (%) (n=1955) (n=1180) Body As A Whole Pain, abdominal 2.9 2.5 Asthenia/fatigue 1.8 1.2 Fever 1.5 0.9 Trauma 1.0 0.8 Digestive System Disorders Dyspepsia 2.1 1.1 Pain, dental 1.7 1.0 Gastroenteritis, infectious 1.5 0.5 Nervous System/Psychiatric Headache 18.4 18.1 Dizziness 1.9 1.4 Respiratory System Disorders Influenza 4.2 3.9 Cough 2.7 2.4 Congestion, nasal 1.6 1.3 Skin/Skin Appendages Disorder Rash 1.6 1.2 Laboratory Adverse Experiences * ALT increased 2.1 2.0 AST increased 1.6 1.2 Pyuria 1.0 0.9 *Number of patients tested (montelukast sodium and placebo, respectively): ALT and AST, 1935, 1170; pyuria, 1924, 1159. The frequency of less common adverse events was comparable between montelukast sodium and placebo. The safety profile of montelukast sodium, when administered as a single dose for prevention of EIB in adult and adolescent patients 15 years of age and older, was consistent with the safety profile previously described for montelukast sodium. Cumulatively, 569 patients were treated with montelukast sodium for at least 6 months, 480 for one year, and 49 for two years in clinical trials. With prolonged treatment, the adverse experience profile did not significantly change. Pediatric Patients 6 to 14 Years of Age with Asthma Montelukast sodium has been evaluated for safety in 476 pediatric patients 6 to 14 years of age. Cumulatively, 289 pediatric patients were treated with montelukast sodium for at least 6 months, and 241 for one year or longer in clinical trials. The safety profile of montelukast sodium in the 8-week, double-blind, pediatric efficacy trial was generally similar to the adult safety profile. In pediatric patients 6 to 14 years of age receiving montelukast sodium, the following events occurred with a frequency ≥2% and more frequently than in pediatric patients who received placebo: pharyngitis, influenza, fever, sinusitis, nausea, diarrhea, dyspepsia, otitis, viral infection, and laryngitis. The frequency of less common adverse events was comparable between montelukast sodium and placebo. With prolonged treatment, the adverse experience profile did not significantly change. The safety profile of montelukast sodium, when administered as a single dose for prevention of EIB in pediatric patients 6 years of age and older, was consistent with the safety profile previously described for montelukast sodium. In studies evaluating growth rate, the safety profile in these pediatric patients was consistent with the safety profile previously described for montelukast sodium. In a 56-week, double-blind study evaluating growth rate in pediatric patients 6 to 8 years of age receiving montelukast sodium, the following events not previously observed with the use of montelukast sodium in this age group occurred with a frequency ≥2% and more frequently than in pediatric patients who received placebo: headache, rhinitis (infective), varicella, gastroenteritis, atopic dermatitis, acute bronchitis, tooth infection, skin infection, and myopia. Pediatric Patients 2 to 5 Years of Age with Asthma Montelukast sodium has been evaluated for safety in 573 pediatric patients 2 to 5 years of age in single- and multiple-dose studies. Cumulatively, 426 pediatric patients 2 to 5 years of age were treated with montelukast sodium for at least 3 months, 230 for 6 months or longer, and 63 patients for one year or longer in clinical trials. In pediatric patients 2 to 5 years of age receiving montelukast sodium, the following events occurred with a frequency ≥2% and more frequently than in pediatric patients who received placebo: fever, cough, abdominal pain, diarrhea, headache, rhinorrhea, sinusitis, otitis, influenza, rash, ear pain, gastroenteritis, eczema, urticaria, varicella, pneumonia, dermatitis, and conjunctivitis. Adults and Adolescents 15 Years of Age and Older with Seasonal Allergic Rhinitis Montelukast sodium has been evaluated for safety in 2199 adult and adolescent patients 15 years of age and older in clinical trials. Montelukast sodium administered once daily in the morning or in the evening had a safety profile similar to that of placebo. In placebo-controlled clinical trials, the following event was reported with montelukast sodium with a frequency ≥1% and at an incidence greater than placebo: upper respiratory infection, 1.9% of patients receiving montelukast sodium vs. 1.5% of patients receiving placebo. In a 4-week, placebo-controlled clinical study, the safety profile was consistent with that observed in 2-week studies. The incidence of somnolence was similar to that of placebo in all studies. Pediatric Patients 2 to 14 Years of Age with Seasonal Allergic Rhinitis Montelukast sodium has been evaluated in 280 pediatric patients 2 to 14 years of age in a 2-week, multicenter, double-blind, placebo-controlled, parallel-group safety study. Montelukast sodium administered once daily in the evening had a safety profile similar to that of placebo. In this study, the following events occurred with a frequency ≥2% and at an incidence greater than placebo: headache, otitis media, pharyngitis, and upper respiratory infection. Adults and Adolescents 15 Years of Age and Older with Perennial Allergic Rhinitis Montelukast sodium has been evaluated for safety in 3357 adult and adolescent patients 15 years of age and older with perennial allergic rhinitis of whom 1632 received montelukast sodium in two, 6-week, clinical studies. Montelukast sodium administered once daily had a safety profile consistent with that observed in patients with seasonal allergic rhinitis and similar to that of placebo. In these two studies, the following events were reported with montelukast sodium with a frequency ≥1% and at an incidence greater than placebo: sinusitis, upper respiratory infection, sinus headache, cough, epistaxis, and increased ALT. The incidence of somnolence was similar to that of placebo. Pediatric Patients 6 Months to 14 Years of Age with Perennial Allergic Rhinitis The safety in patients 2 to 14 years of age with perennial allergic rhinitis is supported by the safety in patients 2 to 14 years of age with seasonal allergic rhinitis. 6.2 Postmarketing Experience The following adverse reactions have been identified during post-approval use of montelukast sodium. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Blood and lymphatic system disorders: increased bleeding tendency, thrombocytopenia. Immune system disorders: hypersensitivity reactions including anaphylaxis, hepatic eosinophilic infiltration. Psychiatric disorders: including, but not limited to, agitation, aggressive behavior or hostility, anxiousness, depression, disorientation, disturbance in attention, dream abnormalities, dysphemia (stuttering), hallucinations, insomnia, irritability, memory impairment, obsessive-compulsive symptoms, restlessness, somnambulism, suicidal thinking and behavior (including suicide), tic, and tremor [see Boxed Warnings, Warnings and Precautions ( 5.1 )] . Nervous system disorders: drowsiness, paraesthesia/hypoesthesia, seizures. Cardiac disorders: palpitations. Respiratory, thoracic and mediastinal disorders: epistaxis, pulmonary eosinophilia. Gastrointestinal disorders: diarrhea, dyspepsia, nausea, pancreatitis, vomiting. Hepatobiliary disorders: Cases of cholestatic hepatitis, hepatocellular liver-injury, and mixed-pattern liver injury have been reported in patients treated with montelukast sodium. Most of these occurred in combination with other confounding factors, such as use of other medications, or when montelukast sodium was administered to patients who had underlying potential for liver disease such as alcohol use or other forms of hepatitis. Skin and subcutaneous tissue disorders: angioedema, bruising, erythema multiforme, erythema nodosum, pruritus, Stevens-Johnson syndrome/toxic epidermal necrolysis, urticaria. Musculoskeletal and connective tissue disorders: arthralgia, myalgia including muscle cramps. Renal and urinary disorders: enuresis in children. General disorders and administration site conditions: edema. Patients with asthma on therapy with montelukast sodium may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition which is often treated with systemic corticosteroid therapy. These events have been sometimes associated with the reduction of oral corticosteroid therapy. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy presenting in their patients [see Warnings and Precautions ( 5.5 )] .

12.3 Pharmacokinetics Absorption Montelukast is rapidly absorbed following oral administration. After administration of the 10-mg film-coated tablet to fasted adults, the mean peak montelukast plasma concentration (C max ) is achieved in 3 to 4 hours (T max ). The mean oral bioavailability is 64%. The oral bioavailability and C max are not influenced by a standard meal in the morning. For the 5-mg chewable tablet, the mean C max is achieved in 2 to 2.5 hours after administration to adults in the fasted state. The mean oral bioavailability is 73% in the fasted state versus 63% when administered with a standard meal in the morning. For the 4-mg chewable tablet, the mean C max is achieved 2 hours after administration in pediatric patients 2 to 5 years of age in the fasted state. The 4-mg oral granule formulation is bioequivalent to the 4-mg chewable tablet when administered to adults in the fasted state. The safety and efficacy of montelukast sodium in patients with asthma were demonstrated in clinical trials in which the 10-mg film-coated tablet and 5-mg chewable tablet formulations were administered in the evening without regard to the time of food ingestion. The safety of montelukast sodium in patients with asthma was also demonstrated in clinical trials in which the 4-mg chewable tablet formulation was administered in the evening without regard to the time of food ingestion. The safety and efficacy of montelukast sodium in patients with seasonal allergic rhinitis were demonstrated in clinical trials in which the 10-mg film-coated tablet was administered in the morning or evening without regard to the time of food ingestion. The comparative pharmacokinetics of montelukast when administered as two 5-mg chewable tablets versus one 10-mg film-coated tablet have not been evaluated. Distribution Montelukast is more than 99% bound to plasma proteins. The steady state volume of distribution of montelukast averages 8 to 11 liters. Orally administered montelukast distributes into the brain in rats. Metabolism Montelukast is extensively metabolized. In studies with therapeutic doses, plasma concentrations of metabolites of montelukast are undetectable at steady state in adults and pediatric patients. In vitro studies using human liver microsomes indicate that CYP3A4, 2C8, and 2C9 are involved in the metabolism of montelukast. At clinically relevant concentrations, 2C8 appears to play a major role in the metabolism of montelukast. Elimination The plasma clearance of montelukast averages 45 mL/min in healthy adults. Following an oral dose of radiolabeled montelukast, 86% of the radioactivity was recovered in 5-day fecal collections and <0.2% was recovered in urine. Coupled with estimates of montelukast oral bioavailability, this indicates that montelukast and its metabolites are excreted almost exclusively via the bile. In several studies, the mean plasma half-life of montelukast ranged from 2.7 to 5.5 hours in healthy young adults. The pharmacokinetics of montelukast are nearly linear for oral doses up to 50 mg. During once-daily dosing with 10-mg montelukast, there is little accumulation of the parent drug in plasma (14%). Special Populations Hepatic Insufficiency : Patients with mild-to-moderate hepatic insufficiency and clinical evidence of cirrhosis had evidence of decreased metabolism of montelukast resulting in 41 % (90% CI=7%, 85%) higher mean montelukast AUC following a single 10-mg dose. The elimination of montelukast was slightly prolonged compared with that in healthy subjects (mean half-life, 7.4 hours). No dosage adjustment is required in patients with mild-to-moderate hepatic insufficiency. The pharmacokinetics of montelukast sodium in patients with more severe hepatic impairment or with hepatitis have not been evaluated. Renal Insufficiency : Since montelukast and its metabolites are not excreted in the urine, the pharmacokinetics of montelukast were not evaluated in patients with renal insufficiency. No dosage adjustment is recommended in these patients. Gender : The pharmacokinetics of montelukast are similar in males and females. Race : Pharmacokinetic differences due to race have not been studied. Adolescents and Pediatric Patients : Pharmacokinetic studies evaluated the systemic exposure of the 4-mg chewable tablets in pediatric patients 2 to 5 years of age, the 5-mg chewable tablets in pediatric patients 6 to 14 years of age, and the 10-mg film-coated tablets in young adults and adolescents >15 years of age. The plasma concentration profile of montelukast following administration of the 10-mg film-coated tablet is similar in adolescents ≥15 years of age and young adults. The 10-mg film-coated tablet is recommended for use in patients ≥15 years of age. The mean systemic exposure of the 4-mg chewable tablet in pediatric patients 2 to 5 years of age and the 5-mg chewable tablets in pediatric patients 6 to 14 years of age is similar to the mean systemic exposure of the 10-mg film-coated tablet in adults. The 5-mg chewable tablet should be used in pediatric patients 6 to 14 years of age and the 4-mg chewable tablet should be used in pediatric patients 2 to 5 years of age. In children 6 to 11 months of age, the systemic exposure to montelukast and the variability of plasma montelukast concentrations were higher than those observed in adults. Based on population analyses, the mean AUC (4296 ng•hr/mL [range 1200 to 7153]) was 60% higher and the mean C max (667 ng/mL [range 201 to 1058]) was 89% higher than those observed in adults (mean AUC 2689 ng•hr/mL [range 1521 to 4595]) and mean C max (353 ng/mL [range 180 to 548]). The systemic exposure in children 12 to 23 months of age was less variable, but was still higher than that observed in adults. The mean AUC (3574 ng•hr/mL [range 2229 to 5408]) was 33% higher and the mean C max (562 ng/mL [range 296 to 814]) was 60% higher than those observed in adults. Safety and tolerability of montelukast in a single-dose pharmacokinetic study in 26 children 6 to 23 months of age were similar to that of patients two years and above [see Adverse Reactions ( 6.1 )] . The 4-mg oral granule formulation should be used for pediatric patients 12 to 23 months of age for the treatment of asthma, or for pediatric patients 6 to 23 months of age for the treatment of perennial allergic rhinitis. Since the 4-mg oral granule formulation is bioequivalent to the 4-mg chewable tablet, it can also be used as an alternative formulation to the 4-mg chewable tablet in pediatric patients 2 to 5 years of age. Drug-Drug Interactions Theophylline, Prednisone, and Prednisolone: Montelukast sodium has been administered with other therapies routinely used in the prophylaxis and chronic treatment of asthma with no apparent increase in adverse reactions. In drug-interaction studies, the recommended clinical dose of montelukast did not have clinically important effects on the pharmacokinetics of the following drugs: theophylline, prednisone, and prednisolone. Montelukast at a dose of 10 mg once daily dosed to pharmacokinetic steady state, did not cause clinically significant changes in the kinetics of a single intravenous dose of theophylline [predominantly a cytochrome P450 (CYP) 1A2 substrate]. Montelukast at doses of ≥100 mg daily dosed to pharmacokinetic steady state, did not cause any clinically significant change in plasma profiles of prednisone or prednisolone following administration of either oral prednisone or intravenous prednisolone. Oral Contraceptives, Terfenadine, Digoxin, and Warfarin : In drug interaction studies, the recommended clinical dose of montelukast did not have clinically important effects on the pharmacokinetics of the following drugs: oral contraceptives (norethindrone 1 mg/ethinyl estradiol 35 mcg), terfenadine, digoxin, and warfarin. Montelukast at doses of ≥100 mg daily dosed to pharmacokinetic steady state did not significantly alter the plasma concentrations of either component of an oral contraceptive containing norethindrone 1 mg/ethinyl estradiol 35 mcg. Montelukast at a dose of 10 mg once daily dosed to pharmacokinetic steady state did not change the plasma concentration profile of terfenadine (a substrate of CYP3A4) or fexofenadine, the carboxylated metabolite, and did not prolong the QTc interval following co-administration with terfenadine 60 mg twice daily; did not change the pharmacokinetic profile or urinary excretion of immunoreactive digoxin; did not change the pharmacokinetic profile of warfarin (primarily a substrate of CYP2C9, 3A4 and 1A2) or influence the effect of a single 30-mg oral dose of warfarin on prothrombin time or the International Normalized Ratio (INR). Thyroid Hormones, Sedative Hypnotics, Non-Steroidal Anti-Inflammatory Agents, Benzodiazepines, and Decongestants : Although additional specific interaction studies were not performed, montelukast sodium was used concomitantly with a wide range of commonly prescribed drugs in clinical studies without evidence of clinical adverse interactions. These medications included thyroid hormones, sedative hypnotics, non-steroidal anti-inflammatory agents, benzodiazepines, and decongestants. Cytochrome P450 (CYP) Enzyme Inducers : Phenobarbital, which induces hepatic metabolism, decreased the area under the plasma concentration curve (AUC) of montelukast approximately 40% following a single 10-mg dose of montelukast. No dosage adjustment for montelukast sodium is recommended. It is reasonable to employ appropriate clinical monitoring when potent CYP enzyme inducers, such as phenobarbital or rifampin, are co-administered with montelukast sodium. Effect of Montelukast on Cytochrome P450 (CYP) Enzymes : Montelukast is a potent inhibitor of CYP2C8 in vitro. However, data from a clinical drug-drug interaction study involving montelukast and rosiglitazone (a probe substrate representative of drugs primarily metabolized by CYP2C8) in 12 healthy individuals demonstrated that the pharmacokinetics of rosiglitazone are not altered when the drugs are coadministered, indicating that montelukast does not inhibit CYP2C8 in vivo . Therefore, montelukast is not anticipated to alter the metabolism of drugs metabolized by this enzyme (e.g., paclitaxel, rosiglitazone, and repaglinide). Based on further in vitro results in human liver microsomes, therapeutic plasma concentrations of montelukast do not inhibit CYP 3A4, 2C9, 1A2, 2A6, 2C19, or 2D6. Cytochrome P450 (CYP) Enzyme Inhibitors : In vitro studies have shown that montelukast is a substrate of CYP 2C8, 2C9, and 3A4. Co-administration of montelukast with itraconazole, a strong CYP 3A4 inhibitor, resulted in no significant increase in the systemic exposure of montelukast. Data from a clinical drug-drug interaction study involving montelukast and gemfibrozil (an inhibitor of both CYP 2C8 and 2C9) demonstrated that gemfibrozil, at a therapeutic dose, increased the systemic exposure of montelukast by 4.4-fold. Co-administration of itraconazole, gemfibrozil, and montelukast did not further increase the systemic exposure of montelukast. Based on available clinical experience, no dosage adjustment of montelukast is required upon co-administration with gemfibrozil [see Overdosage ( 10 )] .