Brief Answer:
Can be gastroenteritis due to depleted age related intestinal flora.

Detailed Answer:
Hi Dear.
Firstly thanks for choosing HealthcareMagic for your query.

Dementia as a cause of Loose stools with mild blood in mucous does not make any sense.Is he on any other particular medicines for dementia other then those mentioned by you above?.
As of now i don't feel it's related to dementia.However age could be a contributing factor.You have not mentioned the duration of his problem.So i would give you the answer assuming it to be short in duration {less then 6 months}.

I would initially suggest you to go for a test called stool routine and microscopy. Presence of bacteria or protozoa in stool can be tested. Some times infestation by toxic bacteria's destroys natural gut flora(good bacteria like lactobacillus) and can cause loose motion etc.Gastroenteritis usually presents with symptoms like bloating ,belching loose stools with increased mucous etc. However its not necessary that all symptoms are always present in every patient.As age of person increases the good bacterial flora present in gastrointestinal tract decreases causing problems with digestion.Even muscles and functions of intestines are diminished with age which can be a cause of loose stools(improper absorption of water by intestines) and increased mucous.
So it can't be dementia related but it can definitely be age related.

Advice-

-Give him Metamucil 2 tsp before going to bed to add bulk to stools.It increases the bulk of stool and help forming stool with good consistency.
Take a good quality probiotic like Econorm three times a day for at least a week.
Medications that can be discussed with your gastroenterologist are-
- Loperamide can be taken by him in doses upto 6mg in a day.It will help him.
-In case stool routine and sensitivity is positive for bacteria or protozoa therapy with cefixime and ornidazole could be taken for 7 days.

For mild blood in mucous a general proctoscopic examination of anal canal should be done to rule out Hemorrhoids or fissure as a possible source of bleeding initially.A stool test for occult blood should be done to be sure if red thing in mucous is blood or not.

Please mention the duration of his problems?
Particular medicines of dementia if he is on?
His advice of medicine is ok as written by you above however add probiotic and metamucil as told by me above.
Some dietary advices are-
Give him a lots of yoghurt(natural probiotic).
Give him a cup of banana and fibrous fruit like peer and oranges daily.
Avoid dairy.
Simple and easily digestible food should be taken for 10 days.
No yolk,Meat or alcohol.
Follow all things i suggested above and tell me how he is feeling in a week.

Regards.

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