Recap: Buddy the Cat with Feline Diabetes goes Closed Loop

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grey tuxido cat relaxing — Here’s Buddy chilling in his Scratchy box.

Closed Loop for a Cat?

Today is Wednesday April 5, 2023, and Buddy is doing extremely well. He has not actually worn an Omnipod since last Sunday – he is well into remission and is getting on just fine with occasional 1.0 Unit injections of Insulin Glargine (generic for Lantus). I gave him one injection this morning at 6:00 when his BG remained high for a while (over 180 mg/dl) – that was the first injection in 36 hours. I’ll get into the history as I pull together the information from the many emails to his veterinarians, Discord posts, texts and other.

Buddy the Cat with Feline Type 2 Diabetes

Meowing grey cat with insulin pump and CGM looking back at you. — Closed-Loop kitty with Dexcom and Omnipod.

Buddy was diagnosed with Type 2 Diabetes on February 24, 2023.

Buddy's blood sugar was 399 mg/dl as measured by a laboratory in his Senior Blood Panel ...

I put a Dexcom G6 Continuous Blood Glucose Monitor (CGM) on him the next day. I only waited that long because I was still trying to figure out how to attach the expensive CGM sensors to a cat so that it does not fall off within minutes, and then I had to wait for the supplies to arrive at my house. And while I waited, I tried to understand whether the CGM’s values would be usable – these things are calibrated for human blood, after all.

Spoiler alert – yes, they are usable. Buddy’s CGM readings were slightly lower every time compared to Blood sugar tests with a Blood Glucose monitor calibrated for cats, using capillary blood from Buddy’s ear at a time the sensor values had been stable for a while.

Important – I am neither a veterinarian nor a physician, and nothing on this website or blog should be viewed as medical advice.

It’s what I do for my cat. Your cat’s diabetes may vary.

For the love of cats, if you consider doing this for your own kitty with diabetes – please inform yourself and work with your vet, and then inform yourself some more.

Important: Please don’t expect your veterinarian to know about closed-loop systems, insulin pumps, etc. That’s neither their fault nor failing – insulin pump therapy is not yet a standard treatment for cats with feline diabetes. Closed-loop insulin therapy is only starting to exist as an (approved) treatment for people.

About me

I am a human with Type 1 Diabetes. I have been using closed-loop systems since 2018. Aside from one “hybrid closed loop”, none of the systems I have used are approved by the FDA. In fact – these are experimental do-it-yourself approaches to living better with diabetes. #wearenotwaiting. As a user of these systems, I owe deep gratitude to many people who have dared to develop, document, and keep improving on real solutions that the medical device industry has long not been able to provide. I’ll add links to the site to these resources.

ProZinc – Not for Buddy

Buddy was initially prescribed ProZinc insulin: 2 units every 12 hours. Seeing his blood sugars in real time, I found within hours that the initial treatment prescribed by Buddy’s veterinarian would not work for Buddy and me.

Bad Situation yields Good Data

The ProZinc insulin worked on Buddy like a regular Insulin works on me: It had a very pronounced action curve and had maybe 6 hours of duration of insulin activity (DIA). He went from 400 mg/dl down to 80 mg/dl within a couple of hours, at which time I gave him a small amount of honey to prevent the cat from getting a hypo. When the insulin stopped working – inside of 6 hours, his BG went right back to 400. Very stressful for Buddy and for me. He was listless and depressed during those episodes of high blood sugar. As a person living with Type 1 diabetes, I appreciate what such a blood sugar “feels” like. I was simply not going to let him be over 400 mg/dl for 6 hours twice a day, to bring him back crashing down with an injection 12 hours after the previous injection and repeat the rollercoaster.

I started augmenting with short-term insulin (that I use), to prevent him from going out of range of the CGM (400 mg/dl).

Buddy’s Blood sugar on ProZinc, and my desperate attempts to keep his blood sugar in-range of the CGM, without going too low.

That was sometime on Saturday around midnight … The good thing about what was otherwise a disaster is that I found out how he responds to short-acting insulin like Humalog. (Very well).

Insulin Glargine’s Action Curve was not flat

We eventually tried a couple of days of insulin Glargine with Buddy, but that simply did not work well either. Glargine is supposed to have almost no “curve” to its action – but for Buddy, that is not the case. So, 2.5 IU of Glargine dropped him by 250 mg/dl and the insulin action was done after 8 hours – and his blood sugar went right back up toward 400.

So, Closed Loop then …

With 4+ years of experience using DIY Artificial Pancreas Systems such as OpenAPS, AndroidAPS, Loop, FreeAPS X, and its new incarnation iAPS on myself, the question was not “IF”, but “HOW” to use an Omnipod in a closed-loop system on my cat.

Visualization: Impact of Closed-Loop on Buddy’s Blood Sugar (and on our collective well-being)

Before iAPS and Closed-Loop: First days on ProZinc + interventions with fast-acting insulin

1.5 days on Glargine. After that, Closed-Loop insulin infusion of fast-acting insulin:

In these curves, the green band marks “normal blood sugar” (80 – 160 mg/dl). The first two days of this set, we attempted injections of insulin glargine twice a day (marked yellow). I switched him on Friday, 3/3/2023 to iAPS, using an Omnipod filled with diluted fast-acting insulin. His time on iAPS is marked blue. Note that the insulin doses are assumed to always be from U-100 insulin by the tracking system and the Omnipod. Since we are using diluted insulin, I have handwritten the actual doses (divide by 10 when U-10 insulin is involved.)

What a difference!

Stress levels went down across the family, we got some sleep at night, and Buddy started to act his normal self again. (Which is essentially “Meow, meow, meow. Let me go outside, feed me, pet me, let me sleep, where is the brush??”)

What Buddy uses as his Artificial Pancreas System

Short-acting insulin
- (Humalog or FIAsp)
- diluted to 10% insulin in 90% diluent (a vet or physician can get that without charge from the insulin manufacturers. I had a few bottles left over from my own “dilution phase”).
administered using a “loopable” Omnipod tubeless pump
- (Omnipod DASH, or Omnipod 3 + Riley Link)
A Continuous Blood Glucose Monitoring System that consists of
- Dexcom G6 sensors
- Anubis transmitter,
The DIY Artificial Pancreas System “iAPS” to close the loop.

a selections of iPhone icons for iAPS. two of the icons are actually a Cat with an Omnipod, others are an insulin pump, and a variations of a circle.

Considerations about Types of Insulin Pumps

Yes: Tubeless pumps such as an Omnipod is working just fine for Buddy (with the right adhesive and with diluted insulin). Insulet’s Omnipod 5 system might work for him, but I don’t have that system around.

I think Omnipod 5 could be a workable “commercial off the shelf” system for cat people not already involved in #wearenotwaiting and DIY Closed Loop stuff for themselves or their loved ones.

No no no: I don’t think putting a cat on a “tubed” insulin pump like a Tandem or Medtronic pump is a good idea. Edit April 2024: Well, maybe a small tubed pump with an angled infusion set would actually work … when Buddy was again on Omnipods for a week in March, I started looking into options – and we actually tested him carrying a 522 MDT pump that was velcroed to his Thundershirt for several hours – but that is where things stopped – the straight MIO infusion set did not work … its cannula goes too deep when it inserts straight – we’d need a set that inserts at an angle, like Omnipods do. Coupled with a Tandem Mobi or similar with a short tubing, that is out of reach for the cat – I can see that working alright, for a limited time and under controlled conditions. Benefit – much smaller adhesive footprint of a regular infusion set, compared to an Omnipods. Obvious risks …

The Stickiest Problem to Solve … Adhesion

My biggest question was how to keep the OmniPod attached to my cat for three days and the CGM sensor attached for at least ten days. That is not a medical question but an engineering problem – adhesion. As I researched the issue, I found that many vets use tissue glue to keep a CGM on a cat or dog, but also found warnings about skin issues caused by using veterinary tissue glue to adhere the sensors. I tried the tissue glue VetBond – (one could call this “medical Superglue”). VetBond works very well to adhere the devices, but it’s not ideal for long-term use and not ideal for the pod’s three-day wear. This is because the tissue glue bonds closely with the skin, and it takes off the kitty’s hair on removal, and if not careful, takes a layer of skin off the cat, leading to skin injuries that don’t heal well if the patient licks the area – as they do.

Next, we tried Skinister Medical Adhesive. Skinister has so far been perfect for what I am using it for. I now use Skinister on myself, e.g., when I want to re-adhere a sensor … it’s seriously awesome stuff – very good adhesion, and it does not damage the skin upon (careful) removal, with or without the companion Skinister Medical Adhesive Remover.

April 2024 Edit: When Buddy was using a sensor and an Omnipod again in March 2024, we settled on using VetBond tissue glue, paired with a harness, and even, a Thundershirt, to prevent Buddy from removing the sensor and the Omnipods. With this, we managed to get full use of these “appliances” – 14 days and 8 hours out of two FreeStyle Libre 2 sensors, and 3 days and 8 hours out of two Omnopods. Buddy’s now “cool” with wearing a harness. (He does many things for treats and positive attention, if given time to adjust.)
We did this in the cool and temperate days of late Winter and early Spring, when overheating is less likely, and we have modified the harnesses to manage the risk of him getting stuck somewhere or otherwise injure himself.
… Treating insulin-dependent diabetes is a complex negotiation of different serious risks, starting with the life-saving Hormon insulin – a little bit too much of which can be fatal quickly, while not enough is fatal midterm … Putting a cat in a harness for extended periods of time carries serious risks that require careful management. We took off the harness often while controlling the cat and stopping him from messing with the pump or CGM, and he immediately went to groom himself in the areas covered by the harness. Cats use grooming also for temperature control, and a harness can lead to overheating, entanglement, etc.