Is it safe to take two zyrtec (cetirizine) a day, one in the morning and one at night?

Sedation: That dose of zyrtec is going to be very sedating. This defeats the purpose of taking zyrtec instead of benadryl (diphenhydramine). That level of sedation will make you a drowsy --> dangerous driver. Have you tried Loratadine or allegra? Do you use Flonase or something like it? Do you regularly flush your nose with a saline/ baking soda solution?

Maximum 10mg: The maximum dosage for Cetirizine is 10 mg daily. Cetirizine is available in 5 and 10 mg tablets. Therefore, a 5mg morning dose followed by a 5mg dose 12 hours later is acceptable. Remember to take it only for allergy symptoms. Good luck!