Is it ok to alternate zyrtec(prescribed) and benadryl (diphenhydramine) (otc) for a few days for an allergy attack. would be z in am and b at pm. 17mth old male

Maybe: Zyrtec makes some people sleepy. They basically work the same but Benadryl (diphenhydramine) works for just a few hours and usually causes more sleepiness. May want to try Allegra (otc generic is fine) in morning if zyrtec causes sleepiness.

Use one-not both.: Zyrtec and Benadryl (diphenhydramine) are both antihistamines-drugs of the same class. Either may work better than the other for your son. Zyrtec typically lasts 24 hours between doses. By alternating, you decrease the effectiveness and gain only an additional likelihood of side effects. Even though the Benadryl (diphenhydramine) is otc, stay with it if it works better, and let your doctor know.

Yes but....: Yes as long as they don't cause drowsiness and thus affecting your alertness. I usually suggest to patients to take something like fexofenadine (allegra) 180 mg during the day and whatever works for them in the evening. Zyrtec causes some drowsiness in slightly over 10% of the people and Benadryl (diphenhydramine) over 30% in my own experience.

Remember the MOA: As an aside, it's important to remember how these meds work. Your allergies are caused by histamine release in the body. Antihistamines block the release of histamine, not its effects. Its important therefore to take allergy medicine prior to experiencing the allergy symptoms. Antihistamines are to prevent allergy symptoms, not get rid of them once they've already shown up.