Glucose level high while on medication

by patricia
(orlando florida)





Question: I am taking metformin and glyburide tablets for type 2 diabetes. When I checked my sugar level today, it was 390 before eating anything.


Does that mean I may be in trouble or that my oral medicines have stopped working?





Quick Answer: A fasting blood sugar of 390 mg/dL (21.7 mmol/L) is severely high. Wash and dry your hands and repeat the test promptly with a fresh strip, but do not delay getting help. If the repeat remains around 390, ketones are present, or you feel unwell, you need urgent same-day medical assessment. Go to the emergency department if the glucose remains at or above 300 mg/dL, you cannot reach a clinician quickly, or you have vomiting, abdominal pain, trouble breathing, confusion, marked drowsiness, severe weakness, dehydration, or fruity-smelling breath.




Answer by: Dr. Albana Greca Sejdini, MD, MMedSc



What should you do now?



  1. Repeat the test promptly. Wash and dry your hands, use a new strip, and confirm that the meter and strips are not expired or damaged.

  2. Check ketones if available. Blood ketones are preferred, but urine ketone strips can also help. Moderate or large ketones require urgent medical care.

  3. Contact a clinician immediately. Do not wait a week to collect readings before seeking advice.

  4. Use emergency care when needed. If the repeat remains near 390 mg/dL, the level is not falling, symptoms are present, or prompt medical advice is unavailable, go to urgent care or the emergency department.




Do not take extra glyburide or metformin on your own. Glyburide can cause prolonged and sometimes severe hypoglycemia if an additional dose is taken. Metformin is not a rapid emergency treatment for glucose of 390 mg/dL. Do not borrow insulin or use an unplanned correction dose.




Have the tablets stopped working?


Possibly, but one reading cannot prove that. Glyburide may become less effective over time in some people, and type 2 diabetes treatment often needs adjustment. However, a sudden rise may also be caused by infection, illness, dehydration, missed doses, steroid medicines, major stress, poor medication absorption, or a problem with the meter or strips.


A late or high-carbohydrate dinner can affect morning glucose, but it should not be used to explain away a fasting result of 390 mg/dL. This reading is far above the usual premeal target and needs urgent review.



What can be checked medically?


Depending on symptoms and the repeat result, a clinician may check:



  • laboratory glucose, blood or urine ketones, electrolytes and bicarbonate;

  • kidney function, hydration status and blood acidity;

  • A1C to estimate recent average glucose;

  • signs of infection, heart problems, steroid exposure or another acute illness;

  • the exact metformin and glyburide doses, timing, adherence and possible interactions.


Kidney function is especially important because metformin use and glyburide dosing require additional caution when kidney function is reduced.



What is safe while arranging care?



  • Take prescribed medicines only as directed unless an urgent-care clinician tells you otherwise.

  • Sip water if you are fully alert, can swallow normally, are not vomiting, and have not been told to restrict fluids.

  • Avoid sugary drinks and alcohol.

  • Do not exercise to force the glucose down, particularly if ketones, illness, weakness or dehydration are present.

  • Bring the glucose meter, medication containers and recent readings to the appointment.



Related Questions




Related Resources




References




Answered by: Dr. Albana Greca Sejdini, MD, MMedSc

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

Last reviewed: July 2026


Medical disclaimer: Educational only—not personal medical advice. Diagnosis and treatment should come from a qualified clinician who knows the patient’s medical history.


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