Section 7: Insulin Treatment and Monitoring

Exogenous insulin administration is the traditional approach to managing diabetic cats. The goals of insulin treatment are the same as with other treatment options: improved glycemic control, mitigation of clinical signs, and improved quality of life for the cat and the clients. Tight glycemic control is not as readily achievable in feline patients as it is in humans.

Insulin Selection

A number of insulins are available for treating DM, and some are more effective than others in feline patients (Table 7.1). The most common choices for cats remain glargine (U-100) (approved for use in people) and protamine zinc recombinant human insulin (PZI) (approved for use in cats and dogs). Both have an acceptable duration of action in cats, provide more consistent glycemic control, and have been commonly associated with inducing diabetic remission. Lente insulin (porcine insulin zinc suspension) is approved for and often used in cats; however, it is not routinely recommended by task force members as a first-choice insulin due to having a shorter duration of action as compared to other starting insulin options. Neutral protamine Hagedorn (NPH) insulin is not considered an acceptable choice for cats owing to a very short (<8 hr) duration of effect.

The basal insulin glargine U-300 is not currently widely used as a standard first choice option although it has been proven effective at controlling hyperglycemia, reducing daily glycemic variability, and achieving diabetic remission in cats.¹ It is more concentrated but less potent than glargine U-100 and therefore should be considered as a separate insulin type and not simply the equivalent of 3 times that of glargine U-100. Because of slowed absorption resulting from the reduced surface area of the injected depot, glargine U-300 exerts a prolonged duration of action possibly allowing for q 24 hr administration in some cats.² Task force members with experience using “peakless” insulin formulations, such as glargine U-300 and basal insulin degludec, report that many treated cats demonstrate a flat time-action profile more like basal insulin secretion and have used these products for treatment of newly diagnosed diabetics or as an option for difficult-to-regulate cats (see Table 7.1).

A potentially promising ultra-long-acting insulin preparation is currently being developed.³ A weekly injection would tremendously relieve caregiver burden and stress and would be a welcome addition to current tools for managing feline DM. Additionally, studies are being done to evaluate the viability of incretin hormones such as glucagon-like peptide-1 (GLP-1) for use in cats to increase pancreatic insulin secretion.⁴

TABLE 7.1: Insulin Products for Cats

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BG, blood glucose; PZI, protamine zinc insulin; U, units.

a. Martin GJ, Rand JS. Pharmacokinetic and pharmacodynamics study of caninsulin in cats with diabetes mellitus. Internal Study Report. 2000.

b. Caney SM. Management of cats on Lente insulin: tips and traps. Vet Clin North Am Small Anim Pract 2013;43(2):267–82.

c. Nelson RW, Henley K, Cole C, et al. Field safety and efficacy of protamine zinc recombinant human insulin for treatment of diabetes mellitus in
cats. J Vet Intern Med 2009;23(4):787–93.

d. Gilor C, Culp W, Ghandi S, et al. Comparison of pharmacodynamics and pharmacokinetics of insulin degludec and insulin glargine 300 U/mL
in healthy cats. Domest Anim Endocrinol 2019;69:19–29.

e. Gilor C, Fleeman LM. One hundred years of insulin: Is it time for smart? J Small Anim Pract 2022;63(9):645–60.

f. Linari G, Fleeman L, Gilor C, et al. Insulin glargine 300 U/ml for the treatment of feline diabetes mellitus. J Feline Med Surg 2022;24(2):168–76.

Insulin Administration

Insulin is administered with either specific insulin syringes or insulin pens. Insulin syringes must match the concentration of insulin to be given; that is, use U-100 syringes with U-100 insulin and use U-40 syringes with U-40 insulin. Insulin syringes with a total volume no larger than 0.3 mL make dose visualization easier. Avoid ultra-short needles (<8mm), as it may be difficult to ensure proper administration through thick fur.

Glargine U-300 requires administration using the manufacturer-provided prefilled insulin pen that dials in increments of 1 unit. An appropriate needle (ideal needle length 10-12 mm) must be used with insulin pens, and the needle must be primed before administering insulin to ensure proper dosing (see the manufacturer provided recommendations). Insulin pens also have a variety of dosing options that range from 1/2-unit increments to 2-unit increments, which may not be suitable for small dosing changes. Clinicians should review manufacturer instructions for the insulin pen being used to identify the recommended injection times (often around 10 seconds), which is the amount of time the needle should remain in the patient’s skin after deploying the injection to ensure the entire dose is delivered to the cat.

Insulin Dosing

Dosing common insulins for cats is not based on units per kilogram, except for glargine U-300 (considered a basal insulin). In overweight or obese cats, all weight-based insulin dosing should be calculated using the cat’s estimated ideal body weight.

For glargine U-100 or PZI, start most cats on 1 unit/cat every 12 hr.

Basal insulin glargine U-300 is dosed at a starting dose of 0.5 units/kg every 12–24 hr.⁵

See also Section 8, Dietary Management, for information on meal timing related to insulin administration.

Monitoring Cats Receiving Insulin

Top 3 Takeaways

• Monitor the cat, not just the numbers.
• In-clinic blood glucose curves are not recommended.
• Most cats will be regulated on less than 4 units of insulin twice daily.

DM is a serious, chronic disease with considerable consequences if the patient is not monitored and managed appropriately. Monitoring is more frequent in the period between starting insulin and achieving glycemic control, but long-term monitoring is essential. In cats achieving remission, approximately 25% were reported to occur within the first 2-3 months following diagnosis, while over 50% occurred within 6 months.^6,7 Monitoring during the first 3-6 months is especially critical to ensure the safety and success of insulin treatment.⁸

Monitoring can be divided into initial and long-term categories. Treatment success is not measured solely by laboratory values but also by improvement and resolution of clinical signs. With good regulation, PU, PD, and PP will drastically improve, and initially, weight gain or cessation of unintentional weight loss are positive indicators.

Initial Monitoring: Glargine U-100 or PZI

Perform the first glycemic check at 5–7 days after initiating treatment with glargine U-100 or PZI. Note clients’ observations of clinical signs and weigh the cat at every visit. If clinical signs have not improved or the cat has not maintained or gained weight, an increased insulin dose is likely needed. Clients should closely monitor their cat for clinical signs of hypoglycemia after starting insulin and if observed, seek veterinary assistance urgently (see Section 15, Figure 15.1). If the patient is hyporexic, vomiting, or generally unwell, assess for ketosis with blood BHB or urine ketone measurement.

Ideally, place a CGM⁹ at the first recheck at 5–7 days, especially if the insulin dose will be increased. The initial regulation period is a critical time for the cat to potentially experience remission or develop hypoglycemic episodes, which makes the CGM an important tool. Hypoglycemia reported by a human-calibrated CGM may not accurately reflect the cat’s true BG, therefore correlate any low BG readings on CGM with a veterinary-calibrated PBGM and clinical signs. It is important to note that occasionally cats will achieve excellent clinical control but have reported BG readings on CGM that are consistently higher (250–350 mg/dL) than the typical targeted range (80–300 mg/dL), highlighting the importance of considering clinical response in therapeutic decision making and not just BG values.

Continue rechecks every 5–7 days. At each recheck, confirm presence or absence of clinical signs, monitor weight, and evaluate glycemic control. The insulin dose can be adjusted every 5–7 days if complete information is available to support safely increasing the dose. If the client is unable to provide accurate and thorough home observations, consider more conservative dose increases and extend rechecks to every 10-14 days. Clients may choose to use urine glucose monitoring for additional information. A negative urine glucose, however, may mean either perfect regulation or a period of hypoglycemia. Fructosamine measurement can be a helpful addition to clinical impression and blood glucose monitoring, but it has limitations (see Section 3, Diagnosing DM in Cats and Section 14, Other Methods for Monitoring Glycemic Data).

In-clinic blood glucose curves are no longer recommended for routine monitoring of diabetic cats. Furthermore, in-home blood glucose curves for cats may also be influenced by stress hyperglycemia, making interpretation challenging (see Section 13, Glucose Monitoring). The use of a CGM, although not specifically calibrated for cats, provides significantly more information than the traditional blood glucose curve. They are simple to place on cats, and even if they do not stay in place for the full 14 days, they provide more complete information than a traditional 8 hr in-hospital or 10–12 hr in-home blood glucose curve.

In-clinic blood glucose curves are no longer recommended for routine diabetic monitoring in cats.

If a cat is not regulated with 4 units or less given twice daily, additional evaluation is recommended before further increasing the dose. Proper insulin handling and administration must be evaluated, as well as considering other disease processes causing IR (see Section 10, Troubleshooting in Diabetic Cats).

Initial Monitoring: Glargine U-300

Initial monitoring of glargine U-300 involves placement of a CGM at the time insulin is started because dosing decisions can be made more quickly than with nonbasal insulins. After starting, the dose can be increased every 1–3 days until an appropriate nadir (80-120 mg/dL) has been achieved. When initiated at once-daily administration, if an appropriate nadir is reached within 2-3 days but BG remains above 300 mg/dL for more than 12 hr per day, a transition to twice-daily administration using the same dose should be considered.¹⁰

Long-Term Monitoring

Once the correct insulin dose is identified, long-term monitoring is relatively straightforward. Recheck at 4–6 wk after establishing the correct dose, and evaluate the client’s impressions, the cat’s overall clinical signs,  and available data such as home blood and urine glucose checks and fructosamine level. If there is any question about the cat’s glycemic control status, including concerns about hypoglycemia, place a CGM. In cats with diabetic remission potential, brief check-ins every 3 months may assist with early detection of downward trends in the BG. Perform routine full rechecks every 6–12 months like those for any cat with a chronic disease, and include a full physical examination and history, CBC, chemistry profile, TT4, urinalysis, and fructosamine measurement.

The 2026 AAHA Diabetes Management Guidelines for Cats are generously supported by Adapet Medical, Boehringer Ingelheim, Dechra, and Merck Animal Health.