Drug Uses ZYRTEC is very useful in treating symptoms of hay fever and other upper respiratory allergies such as stuffy nose, runny nose, sneezing, itching of the nose and throat, and itchy, watery eyes and it works by blocking the action of histamine and reduces the symptoms of an allergic reaction. Usage Following the dosage instructions of your doctor is the best way to use any medication. If you are unsure or do not remember the instructions then you may read the medicine label for more detailed information. You may choose to take ZYRTEC by mouth with a meal to avoid an upset stomach or without one. Drug Class and Mechanism ZYRTEC falls under antihistamine and it works by blocking the action of histamine and reduces the symptoms of an allergic reaction. Missed Dose Despite your best attempts at remembering, if you still miss out on a dose, then take it as soon as you remember about it. But keep in mind that you will have to adjust your next dose by spacing it out by 4 to 5 hours. If this is not possible, then the best thing to do would be to skip the missed dose and continue with your normal dosage schedule. Never try to compensate for the missed dose by taking a double dose together. It may cause adverse effects. Storage Store ZYRTEC at room temperature 20-25 degrees C(68-77 degrees F). Always keep it in a cool dark place that is not directly exposed to sources of heat or moisture and sunlight. Protect it from kids and pets.