My 17yr can i give him alka-seltzer non drowsy day in at 11:30am est them he takes his zyrtac allergy at 2:30pm est?

You could: The two medications alone shouldn't cause problems together but I would be aware that the Alka-Seltzer non-drowsy could interact with other medications that your son may be taking like stimulants or blood pressure medications(this less so the case for most 17 year olds).

Avoid Aspirin: Alka-Seltzer contains Aspirin which should NOT be given to children and teenagers due to the risk of developing a serious and sometimes fatal illness called Reye's Syndrome. This is a neurological condition in which Aspirin causes toxicity to the liver and brain.