The medication is a member of the leukotriene receptor antagonist (LTRA) category of drugs.Although capable of demonstrating effectiveness, the use of such LTRAs like montelukast is typically in addition to or complementary with the use of inhaled corticosteroids or other agents in asthma step therapy.Leukotrienes are chemicals which are released by the body when you breathe in an allergen such as pollen. These chemicals cause swelling in lungs and tightening of the muscles around airways, which further results in asthma symptoms. Montelukast is majorly used to prevent asthma attacks in adults and children as young as 12 months old. Montelukast also prevents exercise-induced bronchospasm in adults and children who are at least 6 years old.
We can treat symptoms of year-round (perennial) allergies in adults and children who are at least 6 months old. It is also used to treat symptoms of seasonal allergies in adults and children who are at least 2 years old.
This medication should not be given to a child without a doctor's advice. Montelukast is also used to prevent exercise-induced bronchoconstriction in adults and teenagers .If montelukast is already taken by the patient on continue bases to prevent asthma or allergy symptoms, do not use an extra dose to treat exercise-induced bronchoconstriction.

Indication
Montelukast is indicated for:
● to prevent asthma attacks
● to treat symptoms of year-round (perennial) allergies 
● used to prevent exercise-induced bronchoconstriction (EIB)

Pharmacology

Mechanism of action:
Cysteinyl leukotrienes CysLT like LTC4, LTD4, and LTE4, among others, are eicosanoids released by a variety of cells like mast cells and eosinophils.  When such CysLT bind to corresponding CysLT receptors like CysLT type-1 receptors located on respiratory airway smooth muscle cells, airway macrophages, and on various pro-inflammatory cells like eosinophils and some specific myeloid stem cells activities that facilitate the pathophysiology of asthma and allergic rhinitis are stimulated.
Alternatively, in allergic rhinitis, CysLTs are released by the nasal mucosa when exposed to allergens during both early and late phase reactions and participate in eliciting symptoms of allergic rhinitis like a congested nose and airway.
Montelukast is a leukotriene receptor antagonist that binds with high affinity , which consequently assists in inhibiting any physiological actions of CysLTs .

Pharmacodynamics:
Montelukast is a leukotriene receptor antagonist that demonstrates a marked affinity and selectivity to the cysteinyl leukotriene receptor type-1 in preference to many other crucial airway receptors like the prostanoid, cholinergic, or beta-adrenergic receptors. the agent elicit substantial blockage of LTD4 leukotriene-mediated bronchoconstriction with doses as low as 5 mg. Montelukast is capable of inhibiting early and late phase bronchoconstriction caused by antigen challenge by 75% and 57% .
It has been documented that montelukast can cause bronchodilation within 2 hours of oral administration.  This action can also be additive to the bronchodilation caused by the concomitant use of a beta agonist.
In clinical trials with adults and pediatric asthmatic patients aged between 6 to 14 years, it was also determined that montelukast can reduce mean peripheral blood eosinophils by about 13% to 15% from baseline in comparison to placebo during double-blind treatment periods, and in the patients aged 15 years and older who were experiencing seasonal allergic rhinitis, the use of montelukast caused a median reduction of 13% in peripheral blood eosinophil counts when compared to placebo as well.

Pharmacokinetics:
Absorption: Montelukast is rapidly absorbed by oral administration. After administration of the 10-mg filmcoated tablet to fasted adults, the mean peak montelukast plasma concentration (Cmax) is achieved in around 3 to 4 hours (Tmax). The mean oral bioavailability is 64%.
The safety and efficacy of medication 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 drug in patients with asthma was also demonstrated in clinical trials .The safety and efficacy of drug 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.
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. Elimination:The plasma clearance of montelukast averages 45 mL/min in healthy adults. 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.
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%).

Contraindication
Contraindications to its use include
renovascular disease , impaired blood flow in the kidneys, severe kidney impairment , volume-depleted patients, a history of angioedema while on an ACE inhibitors, pregnancy and hypotension.

Side Effects
● Headache
● Stomach pain, heartburn, upset stomach
● nausea, diarrhea
● Tooth pain
● Tired feeling,Dizziness
● Fever, stuffy nose, sore throat, cough, hoarseness.
● Mild rash
● Upper respiratory infection
● Earache or ear infection
● Sore throat or cough

Contraindications and Precautions
● Acute Asthma: This medication is not indicated for use in the reversal of bronchospasm in acute asthma attacks .
● Concomitant Corticosteroid use: This should not be abruptly substituted for inhaled or oral corticosteroids.
● Aspirin Sensitivity:Patients with known aspirin sensitivity should continue avoidance of aspirin or non-steroidal anti-inflammatory agents while taking this.
● Eosinophilic Conditions
● Neuropsychiatric Events
● Pregnant patients
●Pregnancy Category B: There are no adequate and well-controlled studies in pregnant women. SINGULAIR can be used during pregnancy only if clearly needed.

Storage
Protect from moisture and light.
Store in original package.