Metformin: Mechanism of Action & Pharmacokinetics

Instructor: Scott Keane

Scott has a Bachelor's degree in Nursing, a Master's degree in Christian Studies, and has taught college level nursing.

Diabetes is a disease that causes a disruption in healthy blood sugar levels. Find out how the antidiabetic drug metformin helps people with diabetes maintain healthy blood sugars.

How Metformin Works

Joe is taking a voyage. Joe is really, REALLY small. He's taking the same trip that a molecule of the drug metformin hydrochloride takes through your body. Joe first travels through your mouth into your stomach (and it's a good thing Joe does not leave a bad taste in your mouth). He then travels into your intestine and is absorbed into your bloodstream. Joe cruises in your bloodstream into muscles, liver, and kidneys. He ends his trip with a pleasant excursion out from your kidneys, taking scenic pictures as he exits your body.

Metformin makes this same voyage. Metformin hydrochloride is a medication used by people with type 2 diabetes to help regulate blood sugar (glucose) levels. It does this by lowering blood glucose. Metformin travels from your mouth into your intestines, where it slows the absorption of glucose into your blood. It travels from your blood into your muscles, where it allows glucose to enter more effectively. It also journeys to your liver, where it slows the release of stored glucose back into your blood. Finally, it exits your body through your kidneys in your urine. All these actions lower blood sugar if you have type 2 diabetes.

Metformin in Your Intestine

Metformin is slowly absorbed into your bloodstream from your intestine. Blood levels of metformin are highest (peak plasma time) 2-3 hours after ingestion if you take the regular release formula. For extended release metformin, blood levels of metformin are highest (peak plasma time) 4-8 hours after ingestion.

Only a portion of the ingested metformin medication is absorbed and utilized by your body. This portion is the bioavailable part. Bioavailability is the amount of a drug absorbed into your circulation that can produce the desired effect. For metformin hydrochloride, 50-60% of the ingested drug is available for the muscles and livers to use.

While in your intestine, metformin also slows the absorption of glucose from your intestine. This helps to lower the body's blood glucose levels. The medication may also cause gastrointestinal upset. Although food slightly slows its absorption and bioavailability, metformin can be taken with some food to prevent indigestion.

Muscle Action

The main action of metformin occurs in your muscles. When you have type 2 diabetes, insulin does not transport glucose into your muscles effectively. This is called insulin resistance. With insulin resistance, your muscles are increasingly resistant to the blood sugar lowering effects of insulin and have less fuel (glucose) for energy. Metformin allows your muscles to be more sensitive to insulin and utilize glucose better. This medication lowers blood glucose by decreasing insulin resistance.

Another action of metformin in muscles is its effect on lipids, or fat. Type 2 diabetics usually have more circulating blood lipids than average. Metformin encourages your muscles to utilize fat instead of storing it. As a result, this drug does not cause you to gain weight. What a deal!

Actions in Your Liver

Metformin also acts in your liver. When you eat more carbohydrates than you need for energy, your liver takes the extra sugar out of your blood and stores it as glycogen. This lowers circulating blood sugar. When you don't eat for a long time, your liver breaks down glycogen and releases it back into your blood as glucose. This raises blood sugar. If you have diabetes your liver automatically releases three times the non-diabetes amount of glucose into your blood. Metformin acts to slow the rate of glucose release by the liver from three times the non-diabetic amount to twice the non-diabetic amount.

Your liver normally makes and stores fat. Diabetes causes excess fat production and storage. This causes fatty liver. Metformin slows fat storage and increases fat utilization, thus causing less fatty liver.

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