*Contributed by Brian T. Bowers, PharmD, RPh, FSVHP, FACVP & Lauralei Schuster, PharmD, FSVHP and in cooperation with the Oregon Veterinary Medical Association.
Diabetes mellitus (DM) is a common disease encountered in canine and feline medicine. As in human medicine, treatment of diabetes mellitus can be challenging, as it requires attention and committed efforts from both the owner and the veterinarian to adhere to a consistent protocol for glycemic control. Community pharmacists must note, however, that there are major differences between diabetes in cats and dogs versus diabetes in humans, specifically in regards to treatment options. Even the slightest variation from a treatment plan can affect the health of the cat or dog, leading to poor glycemic control, which, if left unattended, may lead to life-threatening diabetic ketoacidosis and hypoglycemia.
Type 1 DM is rare in cats and most cats with diabetes have type 2 DM (80%), which is caused by insulin resistance and relative insulin deficiency secondary to β cell dysfunction. Additionally, it is not unusual for cats to go into spontaneous clinical remission within 1-4 months after treatment is initiated, especially if clinical intervention is managed early, aggressively and effectively. Predisposing risk factors for feline DM include: physical inactivity, obesity, older than 8 years of age, high-carbohydrate diet, gender (male neutered), certain breeds, drug therapy (i.e. corticosteroids), and concurrent conditions (i.e. infection, hyperthyroidism, and chronic renal insufficiency). Clinical signs of feline DM may include: polyuria, polydipsia, polyphagia, obesity with recent weight loss, lethargy, dehydration, poor hair coat, hepatomegaly, and neuropathy representative of difficulty jumping, hind limb weakness, and plantigrade posture.
The majority of dogs that have diabetes mellitus are insulin-dependent or Type 1 and are likely to remain diabetic for life due to a relative or absolute lack of insulin secretion secondary to β cell dysfunction/absence which is irreversible. Predisposing risk factors of canine DM include: breed, middle-aged/older females, and concurrent conditions (i.e. infection, drug therapy, obesity, immune-mediated destruction, and pancreatitis). Clinical signs of canine DM include: polydipsia, polyuria, polyphagia, weight loss, dehydration, electrolyte imbalances, metabolic acidosis, frequent urinary tract infections, osmotic diuresis, lameness (due to peripheral neuropathy), or vision loss from cataracts.
Therapy Goals and Assessment:
The therapy goals and assessment for each animal patient is individualized, and treatment may be modified based on response. Blood glucose levels should be maintained between 120 mg/dL to 250 mg/dL in cats and between 100 mg/dL to 250 mg/dL in dogs. Blood glucose control is not as strict as in humans due to the risk of hypoglycemia. While the administration of insulin is the foundation of medical therapy management, other factors are also important for managing DM in canine and feline patients. These factors include clinical remission if possible (cat), minimizing clinical signs (i.e. polyuria/polydipsia), dietary selection, weight control, treatment of concurrent illness, avoiding complications such as ketoacidosis and hypoglycemia [blood glucose <60mg/dL (cat) and <80mg/dL (dog)], avoiding sequelae (i.e. neuropathy or cataracts), and frequent reassessment by the veterinarian.
Choice of Insulin Treatment:
Veterinarians use a variety of veterinary and human insulin products. Only Vetsulin® and ProZinc® are approved by the FDA for use in dogs and cats. All other insulins are used extra-label. It should be noted that veterinary insulins have a concentration of 40 units/mL and require U-40 syringes for dosing to avoid the risk for major dosing errors. Oral hypoglycemics (i.e. glipizide) are not effective in dogs due to the absence of functional β cells. Glipizide may be used in cats when owners are unable or unwilling to administer insulin. However, it has been associated with the destruction of β cells and may become ineffective over time.
- Vetsulin® 40 units/mL (porcine insulin zinc suspension; Merck Animal Health)
- Intermediate-acting insulin most commonly used in dogs
- Initial dose in dogs is 0.25 units/kg subcutaneously every 12 hours after meals
- Duration of action is between 10 to 14 hours in dogs
- Usual dosage (euglycemia maintenance) in cats is 1 to 2 units subcutaneously every 12 hours with or immediately following a meal (this insulin is usually reserved for cats unresponsive to other types of insulin due to its short duration of action)
- Must be shaken well before use to form homogeneous suspension
- Injections must be administered using U-40 syringes only
- Available in 10 mL vial or 2.7 mL pen cartridges (used with VetPen insulin pen)
- Store in the refrigerator and use within 42 days of first puncture
- Insulin glargine 100 units/mL (human recombinant; Lantus®; Sanofi)
- Long-acting insulin commonly used in cats due to its duration of action
- Usual dosage (euglycemia maintenance) in cats is 1 unit subcutaneously every 12 hours with or immediately following a meal
- Although glargine can be used in dogs it is not recommended for initial treatment of newly diagnosed diabetic patients due to unpredictable efficacy
- Available in 10 mL vial or 3 mL prefilled syringe cartridge
- Store in refrigerator and use within 28 days of first puncture
- Do not shake, dilute, or mix with other insulins
- ProZinc® 40 units/mL (PZI human recombinant protamine zinc insulin; Boehringer Ingelheim Animal Health)
- Long-acting insulin for use in cats
- Usual dosage (euglycemia maintenance) for cats is 1 unit subcutaneously every 12 hours with or immediately following a meal
- Although PZI can be used in dogs, it is generally not recommended due to the risk of hypoglycemia
- Injections must be administered using U-40 syringes only
- Available in 10 mL vial
- Store in refrigerator
- Manufacturer does not provide a discard date for punctured vials – owners should be counseled to consult with veterinarian on appropriate beyond use date
- Vial should be rolled gently (not shaken) between palms of hands for to form a homogeneous suspension
- Humulin®-N, Novolin®-N 100 units/mL (NPH U-100 recombinant, Neutral Protamine Hagedorn; Lilly, Nordisk)
- Intermediate-acting insulin that is used in dogs
- Initial dose is 0.25 units/kg subcutaneously every 12 hours
- The duration of action of NPH (6 to 12 hours) may be too short for twice daily dosing in some dogs
- NPH is not recommended for diabetic cats because it is very short acting in the species and does not result in good glycemic control
- Store in refrigerator
- Novolin N available as a 10 mL vial or 3 mL pen; Humulin N available as a 10 mL vial, 3 mL vial, or 3 mL pen
- Vials should be rolled gently (not shaken) between palms of hands to form a homogeneous suspension
- Do not substitute different manufacturers of NPH unless directed by a veterinarian
- Insulin detemir 100 units/mL (Levemir®; Nordisk)
- Long-acting insulin sometimes used in dogs and can be used in cats
- Initial dosage of 0.1 to 0.2 units/kg subcutaneously every 12 to 24 hours, starting at the low end of the dosing range for dogs
- Therapy should be initiated under the supervision of a veterinarian with a blood glucose curve due to long duration of action in some dogs
- Similar dosage as with glargine in cats
- Available as a 10 mL vial or 3 mL pen
- Store both vial and pen in refrigerator until opened; pen should be stored at room temperature after opening (do not refrigerate)
- Once opened, both pen and vial should be discarded after 42 days
- Do not mix or dilute with any other solution or insulin
- Compounded insulin products are not recommended because of concerns about production methods, diluents, sterility, and insulin concentration consistency between lots.
This article is not an all-inclusive practice management topic on diabetes management for dogs and cats but a brief overview of pharmacy practice highlights for the community pharmacists’ understanding. For further information, practicing pharmacists and pharmacy technicians are encouraged to obtain continuing education via Power-Pak C.E.® ‘Veterinary Pharmacy Certificate’ program and to build a library of veterinary references and texts.
Veterinary Pharmacy Certificate POWER-PAK C.E. Continuing Education for Pharmacists and Pharmacy Technicians. Module 7. Providing Pharmaceutical Care and Products for Dogs.
Veterinary Pharmacy Certificate POWER-PAK C.E. Continuing Education for Pharmacists and Pharmacy Technicians. Module 8. Providing Pharmaceutical Care and Products for Cats.
Plumb, D.C. (2015). Plumbs Veterinary Drug Handbook 8th Edition. Ames, Iowa: Wiley-Blackwell
Behrend, E., Holford, A., Lathan, P., Rucinsky, R., Schulman, R. (2018). 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 54(1): 1-21.