Thanks for the answer to my questions.
I suspected that this might be what was given but just wanted to double check. Drugs of this sort haven't been associated with drooling or hypersalivation in cats although I suppose an idiosyncratic reaction could be seen.
There are, however, more common reasons for a cat this age to excessively salivate which I've listed below. In no particular order:
1. Problems in the mouth such as an infected tooth, ulcers, abscesses, foreign body although these seem less likely since he was just examined.
2. Nausea for any reason. The drug you mention can cause diarrhea but nausea isn't one listed either. Again, this doesn't necessarily mean that it wouldn't cause this behavior for him.
3. Ingestion of any noxious substance that they might have groomed off of their bodies (such as flea/tick products) or anything that they might have licked. However, four days is a long time for him still to be drooling if this were the problem.
4. In very young cats, a liver shunt can cause this problem but usually there are other signs such as vomiting weight loss or failure to thrive or balance issues. It would take an ultrasound and additional diagnostics to determine if this is the cause.
I've included this to be complete but it's pretty rare.
5. Early upper respiratory infection or Calici virus. If he starts to sneeze or develop a discharge from his eyes and/or nose, then this is the likely explanation for his drooling.
6. Spontaneous. In some cats, we can’t find an explanation and they will spontaneously stop drooling and we won’t have had any idea why they started in the first place. I've seen cats drool for about a week and then just stop.
As to otc products which may be of help regardless of the underlying cause, Pepcid AC at a dose of ¼ of a 10 mg tablet twice a day may be given.
I hope this helps. Deb