Phenobarbital which acts as a potent cytochrome P450) enzyme inducer, may decrease the AUC of montelukast by upto 40%. However this interaction is not significant. Other P450 inducers such as rifampicin or valproate, may also induce the metabolism of montelukast, but the clinical effects of these interactions are not well established

Chronic asthma

Montelukast appears to be well tolerated in clinical trials . The most common adverse interactions reported are headache, rash, dizziness, and abdominal pain.

Elevated liver transaminases have been reported with montelukast use, but not at a greater incidence than the placebo.

A small percentage of pediatric patients have experienced diarrhea, sinusitis and otitis media during montelukast clinical trials.

Hypersensitivity Pregnancy and lactation The drug has been shown to cross the placena of pregnant rats and rabbits., but there have been no reports of its use in pregnant women. Montelukast is also known to be excreted into breast milk, but only limited information is available. Caution to be excecised prior to initiating montelukast therapy in nursing mothers.

Special precautions:

Motelukast is not indicated for use in the reversal of bronchospasm in acute asthma attacks, including status asthmaticus. Motelukast should not be abruptly substituted for inhaled or oral cortiocosteroids.

Montelukast should be used as monotherapy for the tretment and management of excercise-induced bronchospasm.

Patients who have exacerbations of asthma after excercise should continue to use their usual regimen of inhaled beta agonists as prophylaxis and have for rescue a short acting beta agonist.

Patients with known aspirin sensitivity should continue avoidance of aspirin or non-steroidal anti-inflammatory agents while taking miontelukast.

Clinical monitoring is recommended when systemic coticosteroids reduction is considered in patients receiving montelukast.

Chronic asthma

Dosage-

Adult - 10mg once daily

Child - 2-5 yr 4mg daily 6-14 yr - 5mg daily > 15 yr - 10mg once daily

Pharmacology:

Montlukast is a competitive antagonist. It binds with affinity to the LTD4 receptor , inhibiting bronchoconstrition.

Pharmacokinetics:

Two-third of oral dose is rapidly absorbed from gastrointestinal tract following oral administration, reaching peak levels at 2 to 2.5 hrs after administration of 5mg tablet and 2 to 2.5hrs after administration of 10mg tablet. The 10mg tablet is approximately 64% bioavailable, regardless of whether it is administered with food. The 5mg tablet is 73% bioavailable in the fasting state, but bioavailability declines to 63% when it is taken with food. Montelukast undergoes extensive metabolism in the liver. The mean plasma half life of the drug is 2.7 to 5.5hrs

Bioavailability declines when it is taken with food.

Pregnancy and lactation

Montelukast is also known to be excreted into breast milk, but only limited information is available. Caution to be excecised prior to initiating montelukast therapy in nursing mothers.