Richard Evans wrote:

Ripley, our grand old man, is 17 and has been diabetic for a number of
years. He's on Glargine insulin, 1.5 units in the morning and another
1.5 at night. He's been stable for quite some time. The last couple of
weeks, though, he has been having wild swings in sugar levels: 30 to
400 in the same day.


Ripley is gone. Long story short: He had advanced kidney failure in
addition to the diabetes. We just got back from the vet.

Thanks to all who offered advice, both online and off.