Why is my blood sugar still over 300 while taking Lantus insulin?

by peggy
(denver, co.)






Question


When I first got diabetes, my blood sugar was at 800, then I went on Lantus insulin and metformin and glipizide.


At first, it took a while for my blood sugar to go down. I was really doing well, and now I am at 300 and above most of the time. I take 26 units of insulin every night and still I am having these issues.


I am so tired of giving up all the food that I enjoy and still I am having problems. Please help!


—Peggy, Denver, Colorado





Quick Answer


Peggy, glucose around 300 mg/dL or higher most of the time is not acceptable control, even though it is lower than 800. Contact your diabetes clinician today for prompt review. A basal insulin dose of 26 units cannot be judged as sufficient or excessive without your weight, fasting and after-meal pattern, HbA1c, injection technique, kidney function, medicines, and symptoms.


Do not increase Lantus, metformin, or glipizide by yourself. If glucose remains at 300 mg/dL or above, or you have vomiting, abdominal pain, rapid breathing, fruity breath, severe dehydration, confusion, marked drowsiness, or elevated ketones, seek emergency care.




Answer by Dr. Albana Greca, MD, MMedSc



Hello Peggy,


Your frustration is understandable. The answer is not necessarily more food restriction. Your treatment, insulin delivery, glucose pattern, illness risk, and diabetes type need reassessment.



Why 300 mg/dL Is Still Serious


Glucose of 800 mg/dL may indicate a life-threatening crisis. Falling to 300 is improvement, but 300 remains severe hyperglycemia with risk of dehydration, DKA, hyperosmolar state, and complications.


The old answer incorrectly suggested that 300 after eating might be acceptable. Common adult goals are 80–130 mg/dL before meals and below 180 mg/dL after meals, although goals vary.


Our dangerous blood sugar guide explains when severe hyperglycemia requires urgent care.




When to Go to the Emergency Department


CDC guidance advises emergency evaluation when glucose stays at 300 mg/dL or above and there are signs of diabetic ketoacidosis. Seek immediate help for:



  • Vomiting or inability to keep fluids down

  • Abdominal pain

  • Rapid, deep, or difficult breathing

  • Fruity-smelling breath

  • Severe thirst, dehydration, weakness, or fainting

  • Confusion, unusual behavior, or marked drowsiness

  • Moderate or high urine ketones or elevated blood ketones




Why Might Glucose Stop Responding?



  • Progression of diabetes or reduced insulin production

  • Basal insulin not covering meal-related rises

  • Missed doses, poor storage, expired insulin, or a damaged pen

  • Incorrect technique or injections into lumpy tissue

  • Infection, illness, dehydration, stress, surgery, or steroids

  • Type 1 or another insulin-deficient form being mistaken for type 2


Stress can raise glucose, but persistent results above 300 should never be attributed to stress or age without checking for medical and treatment-related causes.



What Lantus Can and Cannot Do


Lantus is basal insulin. It mainly controls glucose overnight and between meals; it does not directly cover each meal.


If fasting glucose is high, basal insulin may need clinician-guided titration. If fasting is near target but post-meal glucose rises sharply, more basal insulin may cause overnight lows without fixing meal spikes. Another medicine or mealtime insulin may be needed.


The number “26 units” alone does not show whether the dose is right. See our insulin guide.



Check the Insulin Before Assuming It Failed




  • Take Lantus at the prescribed time.

  • Use a new needle and follow the pen safety test.

  • Rotate sites and avoid hard or lumpy areas.

  • Confirm storage, expiration, and in-use discard date.

  • Never share an insulin pen.



Bring the pen, needles, meter, strips, and medicine list so technique can be reviewed.



How Metformin and Glipizide Fit In


Metformin reduces liver glucose output. Glipizide stimulates insulin release and can cause hypoglycemia and weight gain. Its continued use should be reviewed if insulin is intensified.


Do not stop or increase either medicine independently.



What Your Clinician Should Review



  1. Fasting, meal-related, and bedtime readings plus HbA1c

  2. Ketones, hydration, kidney function, and infection

  3. Medicines, steroids, supplements, and missed doses

  4. Insulin storage, pen function, technique, and injection sites

  5. Whether basal-only insulin is sufficient and whether CGM would help


Current treatment options are reviewed in our type 2 diabetes treatment guide.



Should You Exercise When Glucose Is Above 300?


Do not use strenuous exercise as emergency treatment. With ketones, illness, or insufficient insulin, exercise may worsen hyperglycemia or ketosis.



You Do Not Need to Give Up Every Enjoyable Food


Extreme restriction may not correct a medication problem. A dietitian can help include reasonable portions of favorite foods while matching meals to treatment.



  • Do not skip meals while taking glipizide.

  • Pair measured carbohydrate with protein and vegetables.

  • Avoid sugary drinks and record meals with glucose.


Our carbohydrate and diabetes guide focuses on portions and meal structure rather than banning all preferred foods.



What to Do Today



  1. Contact your diabetes clinician and report that glucose is usually 300 or higher.

  2. Recheck after washing and drying your hands, using a new compatible strip.

  3. Check ketones if instructed, especially if ill or glucose remains above 300.

  4. Drink water if safe and you are not on a fluid restriction.

  5. Continue prescribed basal insulin unless emergency clinicians advise otherwise.

  6. Use only a clinician-provided correction plan; do not invent an extra insulin dose.



Remember: glucose above 300 most of the time means the current plan is not working safely enough. It is not acceptable after a meal and is not a reason for harsher food restriction. Promptly review ketones, illness, insulin delivery, glucose patterns, and whether basal-only insulin is adequate.




Written by: Dr. Albana Greca, MD, MMedSc, Family Physician

Medically reviewed by: Dr. Ruden Cakoni, MD, Endocrinologist

Last medically reviewed: August 4, 2026


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References




Safety note: Persistent glucose of 300 mg/dL or higher requires prompt medical assessment, especially with illness, ketones, vomiting, dehydration, breathing changes, or confusion.



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