Metformin: Who Should Take It?

Several prominent endocrinologists gathered in San Diego this past January to develop guidelines for prescribing metformin. Speaking at the American Diabetes Association Post-Graduate course were: Alan J. Garber, MD, PhD, of Houston’s Baylor College of Medicine; Ralph A. DeFronzo, MD, Chief of the Diabetes Division of the University of Texas Health Center in San Antonio; and Jay S. Skyler, MD of Miami.

The doctors presented the following information:

Step One : Try Diet and Exercise

The first step in determining a course of treatment is a test of fasting blood glucose (FBG) levels. If the glycohemoglobin (A1C) is higher than 8.0 and the FBG is over 140 mg/dl, the patient is urged to use diet and exercise alone to lower blood sugars. If this is not successful and the FBG is still over 140 mg/dl or A1C is still over 8.0, the patient is directed to the next step.

Step Two : Try Using a Single Drug

When diet and exercise fail to reduce blood glucose, the patient should be started on either metformin or sulfonylureas. If the patient is not overweight, glyburide (commonly called Micronase, Glynase, or DiaBeta), or glipizide (commonly called Glucotrol) is prescribed up to the maximum dose of 20 mg per day. If the patient is obese, metformin is prescribed up to a maximum dose of 2500 mg per day. Diet and exercise should be encouraged in all cases. If this is not successful and the FBG is still over 140 mg/dl and A1C is still over 8.0, treatment moves to the next step.


Step Three: Try Using Both Drugs

If glucose levels remain inadequately controlled, metformin, glyburide, or glipizide is added to treatment. Those on metformin add glyburide or glipizide, and vice versa. The most common treatment worldwide for type 2 diabetes is the combination of glyburide or glipizide and metformin. If this is not successful and the FBG is still over 140 mg/dl and A1C is still over 8.0, treatment proceeds to step four.

Step Four: Start Insulin

If the combination of both drugs is not keeping blood glucose levels under control, the introduction of insulin is considered. The patient should see a diabetes specialist who can help build a practical regimen around the individual’s lifestyle. The insulin algorithm can seem complicated in light of how many kinds of insulin are on the market and the many ways it can be given. Insulin administration is also threatening to many people because of the use of needles.

Many people are squeamish about needles. This is why metformin or glyburide/glipizide therapy is tried first and insulin is considered only when these fail. A diabetes specialist can help a patient get used to injections by prescribing oral diabetes medicine in the morning and a single dose of NPH insulin at night. This way a patient can grow accustomed to using a needle and also begin to feel better. In many cases patients report an improvement after they start on insulin.

Patients taking both oral diabetes medication and insulin also report less weight gain than patients treated with insulin alone.

Step Five: Take Metformin and Insulin

For those patients who aren’t doing well on insulin therapy alone, are overweight, and are still producing insulin, the addition of metformin is certainly worth a try. A doctor should begin with low doses of metformin to see how the patient reacts-if the result is favorable, doses can be increased up to 2500 mg per day.

Some professionals recommend that a patient’s C-peptide levels be tested during treatment for diabetes. This determines how much insulin the patient’s body is producing naturally. However, the cost and benefit of this test is controversial among endocrinologists, and you should discuss it with your own physician.

DIABETES HEALTH would like to thank R. Keith Campbell, Professor at the University of Nebraska Pharmacy Department for his contribution to this article.

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