Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Charlie is having loose stools which he seems unable to control.
Am I understanding correctly that he is also urine incontinent when he sleeps in his bed (dribbling urine and unable to control it when he is sleeping)?
Some cats with diarrhea
will have stool accidents simply because the frequency of stools and urge to go is such that they don't make it to their litter box. But that should not cause him to have urine incontinence.
What sort of bloodwork was checked on him?
I assume that he had a complete blood count and biochemistry profile. I would also want to check for diseases that will affect his nervous system as well as his gastrointestinal system. I would want to test for feline leukemia, feline immunodeficiency virus and Toxoplasmosis.
If he is truly incontinent then radiographs to look at his spine and the areas around the spine that would affect the nerve roots coming off his spine would important as well. If there are any signs of diskospondylitis (an infection of his vertebrae or bones of the spine) or the soft tissue around his spine then a urine culture would be worth checking to try and determine the cause and appropriate antibiotic as these infections often spread from the urinary tract to the spine.
While probiotics can help rebalance his gut bacteria and may help firm up his stools I am not sure that will be enough in his case if his urinary tract is also affected and he truly is incontinent.
There are some things that you can do at home that may help improve his loose stools.
These include a 24 hour food fast. This should help stop gut spasms and restore normal gut motility. Small amounts of water or clear broth given frequently are fine as he needs fluids after all that he has lost with diarrhea.
Today even with the fast you can start Kao-pectate at 1ml per pound or 1 tablespoon per 15 pounds of body weight every 6 to 8 hours. This is quite safe and will coat his irritated gastrointestinal tract as well as absorbing bacterial toxins. You can use it for several days until his stools look normal. You can find kao-pectate at the drug store.
If he has a tense painful abdomen, continues to have diarrhea with no improvement after being on kao pectate for 24 to 48 hours, becomes very lethargic, begins vomiting or runs a fever greater than 103.5F then he really must be seen by a veterinarian as soon as possible. Make sure to take a fresh stool sample with you when you go to have it checked for parasites.
After his food fast start a bland diet of 2/3 boiled white skinless chicken, all fats and juices drained off the meat, mixed with 1/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1 to 2 tablespoon(s) of canned pumpkin to each meal if you are seeing mucous in his stool as fiber helps soothe an irritated colon.
You can add a probiotic to this mix daily as well. Good brand name products are Fortiflora or Proviable.
Best of luck with your fellow, please let me know if you have any further questions.