C
Carl & Polly & Bob (GA)
Guest
As if there aren't enough variables to think about, I've been doing some reading lately on "carryover" and "overlap", so I thought I'd share...
We often think of Prozinc/PZI as "in and out" insulin. According to what I've read before, compounded PZI is advertised as
- having an onset around +2
- nadir/peak at +4 or +5
- duration of 8-10 hours
Prozinc, according to the manufacturer -
- onset by +3
- nadir/peak between +5 and +7
- duration of 10 to 14 hours
Before anything about carryover or overlap, first there are three other "concepts" I want to mention. These 3 things are critical to determine so that you can figure out what's going on with a cycle of insulin.
1- Onset
2- Nadir
3- Duration
You have to collect data to figure out when onset, and nadir are taking place. And you can get an idea from those as to what type of duration you're getting. A lot of times, I've read (and occasionally said) that a cycle of long duration can indicate a dose that might be "too high". I've reconsidered that. And I've also come to think that there's absolutely nothing wrong with a cycle that lasts "too long", as long as you know what to do with it when you see one. Actually, if you're getting long cycles, you can use that to your advantage, and smile when you see it happen.
Here's something I hadn't read before, from the petdiabetes wiki: PZI is considered to be a "long lasting insulin", although I've usually seen it described as an "intermediate" duration insulin. Yes, compared to a "depot" insulin like Lantus or Levemir, it is "shorter". But according to the wiki, BCP PZI has the following properties:
http://petdiabetes.wikia.com/wiki/BCP_PZI
No type of insulin is absorbed 100% all at the same time. A large portion of a dose might be, but part of the dose will be absorbed more gradually. And other stuff can affect the rate of absorption. Like how hydrated the cat is for instance. I've read on the TR forum that on any given cycle, the rate of absorption can vary by up to 50%. None of this is an exact science. Every cycle is different. So some days you might see a 10 hour cycle, and some days you'll see a 14 hour cycle. I think we go with "shoot every 12 hours" because it makes sense. Twice a day, same time every day, because then you can have a real schedule with this and with the rest of your life. But a cat can't tell time, and they sure don't follow any kind of schedule. They are pretty much on a schedule of "Eat, sleep, play, sleep, eat, groom, sleep, mess with the bean's head, sleep, nap, and sleep. Lather, rinse, repeat. And their "Shuffle" button can't be disabled.
Carryover - http://petdiabetes.wikia.com/wiki/Carryover
Overlap - http://petdiabetes.wikia.com/wiki/Overlap
If you have what seems to be a "long cycle" going on, then you're seeing duration that is longer than usual (assuming your prior data shows duration of 12 hours or less). But what's the problem with that? I don't see one. You can use that knowledge. You can see less of a rise after eating because the first shot isn't completely pooped out. You have a lower preshot, so you can reduce the dose if you want to. The dose will be working against a lower BG than "normal", and you can keep the numbers lower overall. Kitty can spend more time in good numbers, preferably below the renal threshold for as many hours per day as possible. That's got to help, right?
This isn't something you do without careful consideration. Can you test later in the cycle? Do you know what to do with low numbers when they happen? Have you collected enough data to feel good about when onset and nadir usually take place, and do you have a good idea what sort of duration you usually get?
When in doubt, err on the side of caution. Always. But in my opinion, if the choice comes down to "skip" or "shoot", if I were holding the needle, I'd shoot. I'd rather shoot a lower number with a lower dose than skip and pretty much count on a high preshot 12 hours later. To me, that's a missed opportunity, and a loss of momentum. Right when it looks like "progress is being made", you end up right back where you started.
All of this is "my opinion". I'm not a vet, my cat was only on insulin for 10 weeks three years ago, and I didn't test nearly as much or as often as most of you do. What I did do was use a sliding scale for 10 weeks, shot numbers well under 200 regularly, aimed for greens, ignored bounces, and loved Bob like today was our last day together every day. And my reward was two and half years of a life with him that I wouldn't have otherwise had, and that I wouldn't trade for anything.
Carl
We often think of Prozinc/PZI as "in and out" insulin. According to what I've read before, compounded PZI is advertised as
- having an onset around +2
- nadir/peak at +4 or +5
- duration of 8-10 hours
Prozinc, according to the manufacturer -
- onset by +3
- nadir/peak between +5 and +7
- duration of 10 to 14 hours
Before anything about carryover or overlap, first there are three other "concepts" I want to mention. These 3 things are critical to determine so that you can figure out what's going on with a cycle of insulin.
1- Onset
2- Nadir
3- Duration
You have to collect data to figure out when onset, and nadir are taking place. And you can get an idea from those as to what type of duration you're getting. A lot of times, I've read (and occasionally said) that a cycle of long duration can indicate a dose that might be "too high". I've reconsidered that. And I've also come to think that there's absolutely nothing wrong with a cycle that lasts "too long", as long as you know what to do with it when you see one. Actually, if you're getting long cycles, you can use that to your advantage, and smile when you see it happen.
Here's something I hadn't read before, from the petdiabetes wiki: PZI is considered to be a "long lasting insulin", although I've usually seen it described as an "intermediate" duration insulin. Yes, compared to a "depot" insulin like Lantus or Levemir, it is "shorter". But according to the wiki, BCP PZI has the following properties:
Action in cats:
onset 2-5h,
peak 12-24h
duration: maximum 36h.
Generally, depending on an individual cat’s reaction to the insulin and the dosage, BCP PZI will lower blood glucose levels for 10 to 14 hours with a peak in the +6 to +8 timeframe. However, some cats experience shorter or longer duration and earlier or later peaks.
http://petdiabetes.wikia.com/wiki/BCP_PZI
No type of insulin is absorbed 100% all at the same time. A large portion of a dose might be, but part of the dose will be absorbed more gradually. And other stuff can affect the rate of absorption. Like how hydrated the cat is for instance. I've read on the TR forum that on any given cycle, the rate of absorption can vary by up to 50%. None of this is an exact science. Every cycle is different. So some days you might see a 10 hour cycle, and some days you'll see a 14 hour cycle. I think we go with "shoot every 12 hours" because it makes sense. Twice a day, same time every day, because then you can have a real schedule with this and with the rest of your life. But a cat can't tell time, and they sure don't follow any kind of schedule. They are pretty much on a schedule of "Eat, sleep, play, sleep, eat, groom, sleep, mess with the bean's head, sleep, nap, and sleep. Lather, rinse, repeat. And their "Shuffle" button can't be disabled.
Carryover - http://petdiabetes.wikia.com/wiki/Carryover
Carryover or carry-over refers to insulin effects lasting past the insulin's official duration. It's been observed that some long-acting insulins leave an insulin depot[1] under the skin that has a small residual effect that may last anywhere from 12 to 48 hours, after the principal action has ended.
Keep in mind that any substance injected into the body will be removed or broken down gradually, it won't all disappear at once. So even after there's not enough insulin left to make a noticeable dent in blood glucose, there will still be a period of time when small amounts are present and being slowly used up. In long-acting insulins, those small amounts may give a slight boost to the next day's (or three day's) doses.
This small residual effect, if it exists, may mean that the same dose given 3 days in a row will be slightly more effective each day. For example, Dr. Rand mentions in her Lantus studies[2]: "We have found it often takes 3-5 days for a good glucose-lowering effect to be seen in the glucose curves, possibly because of the long duration of action and carry-over effect of glargine."
For terminology's sake, consider the principal action of the insulin to be its onset, peak, and duration. If you shoot insulin again before the duration has expired, there will be overlap. Carryover is whatever small residual effect is left after duration has expired.
Overlap - http://petdiabetes.wikia.com/wiki/Overlap
Overlap refers to the period of time when the effect of one insulin shot is diminishing and the next insulin shot is taking effect. Caregivers can purposefully manage overlap to increase the effect of insulin on their pets' blood glucose levels and thus hold the curve of their blood glucose levels fairly flat.
Suppose a cat gets an insulin shot every 12 hours, gets 15 hours duration from each shot, and is on an insulin that has a three hour onset. During the 3 hours after each insulin shot, there will be two insulin shots working to reduce blood glucose levels: the diminishing previous shot and the rising current shot. This may mean that the ongoing insulin dose should be less than if no overlap was used.
Using overlap safely and effectively requires significant information about and analysis of how a particular insulin works in your pet (its duration, onset, and peak) and how feeding and other forces (such as exercise or sleep) affect your pets' blood glucose levels. Using overlap may result in diminished insulin needs as your pet's blood glucose levels are reduced from the diminishing effect of the previous shot, and possibly also from the carryover effects of previous shots.
Purposeful use of overlap is considered an advanced approach because it usually requires the administration of insulin at blood glucose levels below the renal threshold, or at least lower than some people are willing to administer the next shot. Maximum use of overlap involves administering the next insulin shot at blood glucose nadir, when the effect of the previous shot is at its peak. This technique, ideal in theory, can be dangerous in practise -- you must be sure that the previous shot is about to diminish, which depends on the insulin's action profile in this animal being very predictable. Waiting until the glucose reading has started to rise a bit is more reliable.
If you have what seems to be a "long cycle" going on, then you're seeing duration that is longer than usual (assuming your prior data shows duration of 12 hours or less). But what's the problem with that? I don't see one. You can use that knowledge. You can see less of a rise after eating because the first shot isn't completely pooped out. You have a lower preshot, so you can reduce the dose if you want to. The dose will be working against a lower BG than "normal", and you can keep the numbers lower overall. Kitty can spend more time in good numbers, preferably below the renal threshold for as many hours per day as possible. That's got to help, right?
This isn't something you do without careful consideration. Can you test later in the cycle? Do you know what to do with low numbers when they happen? Have you collected enough data to feel good about when onset and nadir usually take place, and do you have a good idea what sort of duration you usually get?
When in doubt, err on the side of caution. Always. But in my opinion, if the choice comes down to "skip" or "shoot", if I were holding the needle, I'd shoot. I'd rather shoot a lower number with a lower dose than skip and pretty much count on a high preshot 12 hours later. To me, that's a missed opportunity, and a loss of momentum. Right when it looks like "progress is being made", you end up right back where you started.
All of this is "my opinion". I'm not a vet, my cat was only on insulin for 10 weeks three years ago, and I didn't test nearly as much or as often as most of you do. What I did do was use a sliding scale for 10 weeks, shot numbers well under 200 regularly, aimed for greens, ignored bounces, and loved Bob like today was our last day together every day. And my reward was two and half years of a life with him that I wouldn't have otherwise had, and that I wouldn't trade for anything.
Carl