 [ Symptoms ] our 6yo had 1 dose of benadryl in the earlier did not work how many hours must we wait to give him 5mg cetirizine  for two days prior we gave him single doses of claritin which did not work well we tried one does of benadryl around lunch today and after a day outside his allergies are terrible at bedtime would like to try certirizine childrens thanks in advance [ Disease ] benadryl diphenhydramine lasts about four hours so you can use certirizine anytime after four hours