Pharmacokinetics: Peak plasma concentrations of montelukast are achieved in 2-4 hrs after oral administration. The mean oral bioavailability is 64%, montelukast is >99% bound to plasma proteins. It is extensively metabolized by cytochrome P450 isoenzymes CYP3A4, CYP2A6 and CYP2C9 and is excreted principally in the feces via the bile. Metabolism was reduced and the elimination t½ prolonged in patients with mild to moderate hepatic impairment.