Suggest Remedy For Constipation In An Alzhemiers Patient

my husband is 88 yrs. old also alzhemiers 8 yrs. . I am his wife/caretaker 24/7. haven't had problems of con=stipation before, but its been four days and no luck, used miralax twice and this am, 2-tab. milk mag. think he has had enough water and walked him with his outside twice this morning, no luck= what is next?