Alpha-Glucosidase (AG) Inhibitors

The alpha-glucosidase (AG) inhibitor class of type 2 drugs consists of Glyset (miglitol) and Precose (acarbose). Also called starch blockers, these medications must be taken at each meal with the first bite of food in order to be effective. AG inhibitors may be prescribed along with a sulfonylurea drug, metformin, or insulin for some patients.

How They Work

Glyset and Precose work by slowing digestion. More specifically, they block the enzymes responsible for the breakdown of carbohydrates in the intestine, so blood glucose rise is slower and steadier. They may be prescribed for you if you have a hard time keeping your postprandial (after-meal) blood glucose levels under control. AG inhibitors may be a preferred therapy in overweight patients, since they do not promote weight gain like the sulfonyl-ureas and TZDs do.


If a blood sugar low occurs when Glyset or Precose is taken in conjunction with a sulfonylurea or insulin, it should be treated with glucose gel or tablets. AG inhibitors slow the digestion of sucrose, so things like table sugar and sucrose-containing foods are not good choices as hypoglycemic treatments.

Possible Side Effects

Because of the way they work, the AG inhibitors' side effects are primarily gastrointestinal, and include bloating, diarrhea, gas, and cramping. However, like metformin, the uncomfortable side effects can be greatly reduced by starting with a small dose and gradually increasing it.

People with serious gastrointestinal disorders, including intestinal disease or obstructions, inflammatory bowel disease, and colonic ulceration, should not take AG inhibitors.

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