Pharmacology
Pharmacodynamics
Zafirlukast is an antagonist of cysteinyl leukotriene receptor 1 (CysLT1), a receptor found throughout the smooth muscle of the lungs, within interstitial lung macrophages (white blood cells that operate in the interstitial space of the lungs), and rarely in epithelial cells. CystLT1 is a receptor for a specific class of leukotrienes that contain the amino acid cysteine. These cysteinyl leukotrienes include leukotriene C4, leukotriene D4, and leukotriene E4, all of which are produced by inflammatory cells like eosinophils, basophils, and macrophages in the lungs. Through their action on CysLT1 these leukotrienes can trigger bronchoconstriction, a state in which the bronchial passages of the lungs constrict, leading to the characteristic, reactive airway symptoms associated with bronchial asthma. The other pro-inflammatory effects of leukotrienes, such as their inhibition of mucus clearance and their stimulation of mucus secretion and edema, are thought to play a role in the characteristic symptoms of allergic rhinitis (also called hay fever). By inhibiting the action of these specific leukotrienes, zafirlukast is thought to exert an anti-inflammatory effect against leukotriene-mediated inflammatory conditions. Pharmacokinetics
Absorption
Zafirlukast is rapidly absorbed into the bloodstream following oral administration, reaching peak plasma levels within 3 hours of taking the dose. The peak plasma level is the maximum concentration of zafirlukast in the blood. Distribution
Zafirlukast is moderately distributed into the bodys tissues, with an apparent steady state volume of distribution of 70 liters. Zafirlukast is highly plasma protein bound, 99% bound to albumin.
Available forms
There are two dosage forms for zafirlukast, notable for their age-adjustments. The 20 mg tablet is for adults and children older than age 12, whereas the 10 mg tablet is for children between the ages of 5 and 12. Tablets should be stored at room temperature, out of direct sunlight, and away from sources of moisture.Tablets are for oral administration only. Specific populations
Pediatrics
As a general rule, leukotriene receptor antagonists like zafirlukast are more effective in children that are younger and whose asthma is less atopic. Atopy refers to a predisposition towards developing allergic conditions, including asthma, hay fever, and eczema. Geriatrics
The hepatic clearance of zafirlukast is impaired in adults 65 years of age and older, resulting in a 2–3 fold increase in the maximum plasma concentration and the total area under the curve. Zafirlukast may increase the risk for infections (7.0% vs 2.9%, zafirlukast vs. placebo incidence respectively), especially lower respiratory tract infections, in older adults, though the infections noted were not severe. Pregnancy
Zafirlukast is considered to be "pregnancy category B." This is due, in part, to the wide safety margin of zafirlukast in animal studies investigating teratogenicity. No teratogenicity has been observed in doses up to 2000 mg/kg/day in cynomolgus monkeys, representing an equivalent 20x exposure of the maximum recommended daily oral dose in human adults. However, spontaneous abortions occurred in cynomolgus monkeys at 2000 mg/kg/day, though the dose itself was maternally toxic. Lactation
There is limited research on the use of zafirlukast in women whom are breastfeeding.