Welcome to FDMB.
Let me add a bit of detail to Larry's post just in case you're not familiar with some of the following information. Caninsulin is a U40 insulin. The U40 refers to the concentration of the insulin. You use a syringe that matches the concentration of the insulin. In other words, with Caninsulin, you should be using a U40 syringe.
When you switch to Lantus, you will be using a U100 insulin. If you're currently using a U100 syringe, you can keep doing so. Most people. use a U40 syringe with Caninsulin.
Are you home testing? One reason I'm asking is that if you switch Lisa to a canned food diet, her blood glucose numbers may drop into a lower range. The Purina dry food is not particularly low in carbohydrates despite it being called "diabetic" food. Can you let us know what food you're considering switching to?
In addition to being able to monitor the effect of a diet change, home testing your cat's blood glucose is the only way to know if it's safe to give insulin. It also allows you to adjust the dose when necessary.
