Yes
Yes.
does diarrhoea interfere with absorption of drugs
The function of the ileum is mainly to absorb vitamin B12 and bile salts and whatever products of digestion were not absorbed by the jejunum.
Some interactions between vitamins may lead to its poor absorption. For instance, iron supplements do not go together well with zinc and may also interfere with absorption of vitamin E. Calcium impedes the absorption of iron that's why they should not be taken together.
Examples of such diseases are celiac disease (chronic nutritional disorder), cystic fibrosis, and cholestasis (bile-flow failure or interference).
A lack of vitamin metabolism (vitamins K, D, A, E) because of the absence of bile to assist in the absorption of nutrients from the intestines.
Vitamin A
See the related link below for an article on what foods may interfere with the absorption of Dilantin.
vitamin A
no
Animal studies have concluded that vitamin C enhances chromium absorption of insulin.