There is no information available that Neosine Duo interacts with the ingredients in Immunotrophin syrup. Therefore, I see no contraindications to give them to a 3-year-old child on the same day, keeping a 2-hour interval. Immunotrophin syrup should be administered once a day between meals (1 scoop), while Neosine Duo should be administered as directed by a doctor (the dose is selected based on body weight and administered 3/4 times a day). Leaflet: https://www.gdziepolek.pl/produkty/98419/neosine-duo-syrop/ulotka I enclose additional materials: https://www.gdziepolek.pl/artykuly/jak-wzmocnic-odpornosc-u-dziecka-przed-pojsciem-do-szkoly