Introduction
High blood sugar, or hyperglycemia, is the main sign of diabetes mellitus in dogs. This occurs when the body does not produce enough insulin or cannot properly use the insulin it makes. Insulin is a hormone that helps cells absorb glucose from the bloodstream and turn it into energy.
Without enough insulin, glucose builds up in the blood instead of being used for energy. This causes blood sugar levels to become abnormally high. To manage diabetes and regulate blood sugar, daily insulin injections are typically prescribed. This provides the insulin dogs need when their bodies cannot produce enough on their own.
Even with insulin therapy, some diabetic dogs may still have higher than ideal blood sugar levels. There are several potential reasons why insulin injections may not fully lower blood glucose in dogs with diabetes.
Normal Regulation of Blood Sugar
In healthy dogs, blood sugar is tightly regulated by the hormones insulin and glucagon to remain within a normal range. After a meal, the pancreas releases insulin, which allows glucose from digested food to enter cells throughout the body to be used for energy. Insulin lowers blood sugar levels by promoting glucose uptake and storage as glycogen in the liver and muscles. The pancreas also secretes glucagon when blood sugar is low, which signals the liver to break down glycogen into glucose and release it into the bloodstream to raise blood sugar levels. This interplay between insulin and glucagon keeps blood sugar levels balanced. According to Cornell University, normal blood sugar levels in dogs range from 75 to 120 mg/dL after a 12 hour fast.
Causes of Diabetes in Dogs
Diabetes in dogs is often caused by the destruction of insulin-producing cells in the pancreas, leading to insulin deficiency and excess glucose in the bloodstream (AKC, PetMD). There are several potential underlying causes:
– Pancreatitis – Inflammation of the pancreas damages the insulin-producing cells. This is a very common cause in dogs.
– Autoimmune disease – The dog’s immune system attacks and destroys the insulin-producing cells. This accounts for about 50% of diabetes cases in dogs.
– Insulin resistance – Cells become resistant to the effects of insulin. More insulin is needed to control blood sugar which can eventually exhaust the pancreas.
– Obesity – Excess fat leads to increased insulin resistance and eventual insulin deficiency.
– Infection – Infections of the pancreas can damage insulin production.
– Cancer – Tumors in the pancreas interfere with insulin production.
– Certain drugs – Steroids and some other drugs can trigger diabetes by causing insulin resistance.
– Genetic predisposition – Some dog breeds are more prone to developing diabetes, indicating a genetic component.
In most cases, the root cause leads to low or absent insulin production, causing diabetes and dependence on injected insulin to control blood sugar levels.
How Insulin Works
Insulin is a hormone produced by the pancreas that allows glucose (sugar) in the bloodstream to enter the cells to be used for energy. In dogs with diabetes, the pancreas either does not produce enough insulin or the cells become resistant to insulin, leading to high blood sugar levels.
Injectable insulin works by supplementing the insulin that the dog’s body cannot produce on its own. The injected insulin binds to insulin receptors on cell surfaces, triggering a signaling cascade that allows glucose transporters to move to the cell surface. This allows glucose to move from the bloodstream into the cells, lowering blood sugar levels.
Typically, an intermediate-acting insulin such as NPH or lente insulin is used in dogs. This starts lowering blood glucose within 1-2 hours and has a peak effect 4-10 hours after injection, with effects lasting 12-18 hours. The insulin dose and timing is adjusted based on the dog’s individual response.
So in summary, injectable insulin can help lower and control blood sugar in diabetic dogs by facilitating the movement of glucose into cells, when the dog’s own pancreas cannot produce sufficient insulin.
Why Insulin May Not Lower Blood Sugar
There are several reasons why insulin may not be effectively lowering your dog’s blood sugar levels as expected:
Incorrect insulin dose – Your vet determines the starting insulin dose based on your dog’s weight and other factors, but this dose often needs to be adjusted over time. If the current dose is too low, it will not lower your dog’s blood sugar enough. Your vet can help determine if an increase is needed through glucose curve tests. However, increasing the dose drastically without guidance can lead to hypoglycemia. [1]
Insulin timing – Giving insulin at inconsistent times or changing when it is given relative to meals can affect how well it controls blood sugar. Ideally, once a schedule is established, insulin should be given at the same times every day. [2]
Insulin storage – Insulin that gets too hot or cold or expires can become less effective. Always follow storage guidelines and do not use insulin beyond the expiration date. [3]
Other medications – Some medications like steroids can counteract insulin. So can conditions like infections. Always notify your vet about any new medications or health changes. [1]
Incorrect Insulin Dose
One of the most common reasons a dog’s blood sugar remains high after insulin is an incorrect insulin dose. According to the VCA Hospitals, the starting dose of insulin for diabetic dogs is typically 0.25-0.5 units/kg every 12 hours. However, each dog requires individualized dosing based on factors like their response to insulin, other medications, and overall regulation of blood glucose.
If the insulin dose is too low, it will not be enough to lower the dog’s blood sugar into the normal range. As per the AAHA guidelines, if a dog’s blood sugar nadir is consistently above 150 mg/dL, the insulin dose likely needs to be increased by 10-25% depending on the dog’s size and degree of hyperglycemia. Slow increases allow the dose to be adjusted precisely based on the dog’s response.
Conversely, if the insulin dose is too high, it can cause life-threatening low blood sugar or hypoglycemia. Therefore, doses must be carefully monitored and increased gradually under veterinary supervision. Frequent blood glucose curve monitoring helps determine if adjustments need to be made to achieve optimal regulation. The goal is finding the ideal dose that maintains blood sugar within the normal 80-120 mg/dL range.
Insulin Timing
Proper timing of insulin injections is critical for maintaining normal blood sugar levels in diabetic dogs. Insulin should ideally be given right before a meal, with no more than 1 hour between eating and injecting insulin according to Caldwell Animal Hospital1. This helps prevent spikes in blood sugar after eating. If insulin is given too long after a meal, there can be a period of 2-3 hours of high blood sugar before the insulin starts to work according to ADW Diabetes2. High blood glucose over time can cause damage to organs and tissues.
Giving insulin too early, more than 1 hour before a meal, can also lead to blood sugar spikes. This is because the insulin starts working before the dog eats, potentially causing hypoglycemia. Then once the dog eats, blood sugar rises rapidly without enough active insulin present.
Mistiming insulin injections often happens when meal times or insulin routines get off schedule. It’s important to maintain a consistent schedule day to day. Checking blood sugar curves can help identify if mistimed insulin is leading to abnormal fluctuations in blood glucose.
Insulin Storage
Proper storage of insulin is critical to maintain its effectiveness. Insulin is a very sensitive medication that can lose potency if not stored correctly.
According to the Cornell University College of Veterinary Medicine, “Insulin is sensitive and must be stored carefully, not too cold or too hot. Even shaking it too vigorously can harm this medication. Some insulins need to be refrigerated, while others should be kept at room temperature.”1
Insulin should be kept refrigerated between 36°F and 46°F (2°C and 8°C). It should not be frozen or exposed to direct sunlight or high temperatures, as this can destroy the insulin molecules and make the medication less effective. Keeping insulin too cold in the refrigerator can cause it to crystallize or precipitate out of solution.
Shaking insulin vigorously can denature the proteins in the solution, reducing its potency. Gentle rolling or tipping of the vial is recommended to mix the insulin before drawing a dose.
Following the storage recommendations from your veterinarian and the insulin manufacturer is important to maintain the medication’s strength and effectiveness. Improperly stored insulin may not lower your dog’s blood sugar as expected.
Other Medications
Certain other medications can interfere with insulin absorption and lead to persistently high blood sugar in dogs on insulin therapy. Some types of drugs that may cause issues include:
- Steroids like prednisone – These drugs can interfere with insulin’s ability to lower blood sugar (1).
- Diuretics like furosemide – Diuretics like Lasix can flush insulin out of the body before it absorbs properly (2).
- Heart medications like digoxin – Heart drugs may enhance insulin’s blood sugar lowering effect leading to hypoglycemia (3).
- Thyroid medication – Excess thyroid hormone can counteract insulin (4).
- Some antibiotics – Drugs like erythromycin can increase insulin absorption and risk hypoglycemia (4).
If your dog is on any of these types of medications along with insulin, let your veterinarian know. They may need to adjust the insulin or other medication dose to balance everything appropriately.
When to Seek Veterinary Help
If your diabetic dog’s blood sugar remains high after receiving insulin, it’s important to seek veterinary help promptly. According to the Cornell University College of Veterinary Medicine (https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/health-info/what-diabetes-mellitus), uncontrolled high blood sugar over time can lead to serious complications like cataracts and diabetic ketoacidosis, which can be life-threatening.
The American Animal Hospital Association (AAHA) guidelines on diabetes management (https://www.aaha.org/aaha-guidelines/diabetes-management/troubleshooting/) recommend seeing your vet right away if your dog is showing signs of poor blood sugar control like increased thirst, increased urination, weight loss, or weakness. Bring a record of your dog’s insulin doses, blood glucose readings, food intake, and any concurrent medications.
Veterinary assistance is especially crucial if your dog is exhibiting symptoms of hypoglycemia like lethargy, confusion, unsteadiness, or seizures or symptoms of diabetic ketoacidosis like vomiting, rapid breathing, fruity breath odor, and dehydration. These require emergency veterinary treatment.
Your vet can troubleshoot why your dog’s blood sugar remains high by evaluating factors like inadequate insulin dose or frequency, insulin type, timing related to meals, proper storage and handling of insulin, effects of other medications, overall regulation of diabetes, and concurrent health issues. They can then adjust treatment to better control your dog’s diabetes.