Hi and thank you so much for this query. These drugs are particularly prescribed to stop vomiting but intended to control the infection that is causing this vomiting. They are safe medications and can be taken together without great fear of a possible drug interaction. If you think he can not tolerate any medication by mouth, please talk to his doctor about the possibility of administering the through alternative means like injections and fluid administration to avoid dehydration and it consequences. I hope this helps. I wish you well and feel free to ask for more information should need be. Thanks. Dr. Ditah, MD.