Can a 7year old boy diagnosed with allergies take singular and zyrtec simultaneously?

Yes: Zyrtec is an antihistamine while Singular is a leukotriene receptor antagonist. Leukotrienes are chemicals your body releases when you breathe in an allergen (such as pollen). Leukotrienes cause swelling in your lungs and tightening of the muscles around your airways, which can result in asthma symptoms. Singulair (Singular) works by blocking leukotrienes.

Yes: They act on different parts of the allergy symptom pattern & do not interfere with each other.