Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Jack has been diagnosed with cancer and has now developed diarrhea.
I'm not generally a huge fan of Imodium (Loperamide) to treat loose stool issues for a number of reasons:
I've seen a number of dogs develop side effects such as constipation, bloat, and sedation with other, potentially, more serious adverse effects also possible: paralytic ileus, toxic megacolon, pancreatitis, and central nervous system signs.
In addition, collies, shepherds, related breeds, or other dogs who have a defective MDR-1 gene mutation may be overly sensitive to Imodium and it's use should be avoided.
If there are no other options available, then no more than 2 or 3 doses should be given which would be about 1 mg twice daily.
If Jack isn't vomiting nor currently taking steroids or non-steroidal anti-inflammatory medications, then over the counter Pepto Bismol is what I'd recommend instead. The dose would be 1 ml per 10 lbs of body weight 2-3 times a day.
Pepto bismol should not be given to vomiting dogs sincei t contains salicylates (the active ingredient in Aspirin) which can irritate the stomach.
It can also turn the stools a greenish or grey color.
I'd also start him on a good quality, canine probiotic such as FortiFlora or Resources Protegrity GI if you haven't already. These products can be extremely useful for gastrointestinal issues (and to help strengthen the immune system as well).T hey may be available at local pet/grain stores or can be purchased online.
I would also continue the bland diet of boiled, skinless chicken breast and boiled 20-minute white rice, small meals through the day.
I hope this helps. Deb