Alpha-glucosidase inhibitors or starch blockers help control blood sugars by slowing down the digestion of complex carbohydrates. This greatly reduces the spikes that may be seen in blood sugar after meals and, surprisingly, also tends to lower the fasting blood sugar. The two medications in this group, Precose and Glyset, are taken with every meal.

Starch Blockers
Target Organ: Intestine
Action: Slow breakdown of carbs in intestine
Lowers HbA1c by 0.7% to 1.0%
Time to reach maximum effect: 1 hrs
Taken: before meals with first bite of food

Precose (acarbose) 4 hrs 25-300 mg 3

Glyset (miglitol) 4 hrs 25-300 mg 3

Side Effects: bloating, nausea, diarrhea, excess gas, abdominal pain

Contraindications: liver disease, bowel or intestinal disease, intestinal obstruction

Like metformin, Precose had been used in Europe for several years before it was approved in the U.S. Its action is quite different from other diabetes medications in that it works by inhibiting enzymes in the intestine that break down carbohydrates. This slows the digestion of carbohydrates in the small intestine, which, in turn, slows the rise in the blood sugar after a meal. This slower rise in glucose level matches a person's reduced internal production of insulin to improve blood sugar control.

The way in which starch blockers work is also the source of their side effects. Although they are very safe because they usually enter the bloodstream in negligible amounts, their side effects within the intestine can be annoying. If digestion is greatly inhibited, abdominal bloating, gas, and diarrhea can result.

A very good way to minimize or prevent intestinal side effects is to start these medications at minimal doses and then gradually increase them as tolerance improves in a week or so. Half of the smallest tablet can be started before one meal a day, then gradually the dose can be increased and extended to all meals this way. Side effects tend to decrease over time, allowing doses to be increased. Anyone who has problems with digestion or absorption will need to take extra care with these medications.

If Precose and Glyset are taken with insulin or another diabetes medication that can cause low blood sugars, the lows are best treated with glucose tablets or a glucose gel. Digestion of sugar, fruit, and fruit juice is delayed by starch blockers, so they will not raise a low blood sugar as quickly.

Like metformin, these drugs do not cause low blood sugars when used alone, nor do they cause weight gain or raise insulin levels. Because they work in a unique way, they can be added to other oral agents to improve blood sugar results.