There are a lot of good medicines available for veterivary use that are the same as the ones for humans. That is why they sometimes impound vet supplies when there is a hurricane, flood, tornado or other potential disaster.
Midstates, Rural King, TSC, Big Blue Stores all carry a good supply. Maybe even Farm Bureau CO-OP.
And places like Wal-mart and Walgreen will fill prescriptions for your critter, too.
(And you can maybe pull rank on your dog, if not the wife)