Is it safe to take 20mg montelukast in one day?

Montelukast : Montelukast has been administered at doses up to 200 mg/day to adult patients for 22 weeks and, in short-term studies, up to 900 mg/day to patients for approximately a week without clinically important adverse experiences. I don't recommend that you take more than 10mg at night. There is no indication to go over 10mg.

Allergy evaluation : If your allergic symptoms are not well controlled. consider an allergy evaluation. Avoid possible triggers such as pollen,dust,mold and pet dander. Rinse eyes and nose with saline.