Sorry no one has gotten back to you sooner.
The biggest difference between Prozinc and Lantus resides in their pharmacology. Lantus is a
depot-type of insulin. Depot medications release more slowly -- sometimes not requiring another injection for up to a month, although this is not the case with Lantus. When you inject Lantus, it forms microcrystals that are deposited into the fat tissue. Most of these crystals slowly dissolve over the 12-hour cycle but some do not creating carryover from one dose into the next cycle. The action of the depot is what gives Lantus its long duration and ultimately, its flat cycles.
The action of the depot also makes Lantus an insulin that works best with consistency. It initially takes the depot about 5 - 7 days to form/stabilize. Thereafter, any time you make a dose change, you need to allow the depot to re-stabilize. Because Prozinc doesn't have a depot, there is no issue with making a dose change based on the pre-shot number if you need to do so. With Lantus, back-to-back changes in dose typically yield wonky numbers due to the depot not having the opportunity to catch up with the changes in the dose. In addition, perhaps more than any other insulin (except Levemir), Lantus dose changes are based on the nadir. This also means it's important to get spot checks as well as pre-shot tests. If you follow the Tight Regulation Protocol, you hold doses for 3 days before evaluating the effectiveness of the dose unless a dose reduction is indicated. If following Start Low Go Slow, you hold the dose for a week.
Not only is consistency with regard to dose important, consistency with respect to time is also a consideration. You have more flexibility with shot time with Prozinc. Lantus does best if you shoot as close to every 12 hours as possible. Again, this is due to the depot. An early shot acts like a dose increase whereas a late shot acts like a dose reduction.
In looking at Shasta's spreadsheet, I think you are seeing some bouncing. Bounces occur regardless of the insulin so you're as likely to see it with Lantus as with Prozinc. When Shasta's numbers drop closer to normal range, her liver and pancreas go into panic mode because she's no longer used to being in normal BG numbers. When this happens, a stored form of glucose is released along with counterregulatory hormones and they cause the upward spike in numbers. It can take up to at least 3 days for the bounce to clear. Shasta's AM cycle on 10/9 is a good example of a bounce.
What's not entirely clear to me is whether or not your getting the kind of duration you want from Prozinc. There's not a consistent pattern of numbers rising a lot at the end of the cycle. It may be a matter of not hanging on to doses quite as long. On the other hand, some cats just do better on a different insulin.
I'm likewise tagging
@JanetNJ since she's more experienced with Prozinc than I am and she can weigh in on whether it would make sense to stick with Prozinc vs making a switch.
