The α-Glucosidase inhibitors primarily act to decrease postprandial hyperglycemia by slowing the rate at which carbohydrates are absorbed from the gastrointestinal tract. They act by competitively inhibiting -glucosi-dases, a group of enzymes in the intestinal brush border epithelial cells that includes glycoamylase, sucrase, mal-tase, and dextranase. The prolongation of the intestinal absorption of carbohydrates results in a blunted insulin response, keeping postprandial hyperglycemia under control. To be effective, α-Glucosidase inhibitors must be taken before or with meals. Theoretically, the - glucosidase inhibitors are most beneficial in patients with mild to moderate diabetes whose diet is more than 50% carbohydrates. α-Glucosidase inhibitors are not approved for used in type I diabetes.
Acarbose (Precose) is an oligosaccharide derivative that has a higher affinity for the - glucosidase enzymes than do other dietary oligosaccharides. Systemic ab-sorption of acarbose is very low (~2%), with most being broken down in the intestine to several metabolites. About half of the orally administered acarbose is ex-creted unchanged in the feces, while the remainder, some of which is systemically absorbed, is renally ex-creted. Acarbose may be associated with hepatotoxicity in rare instances.
Miglitol (Glyset) is another α-Glucosidase inhibitor, but in contrast to acarbose, miglitol is systemically ab-sorbed prior to its activity in the small intestine. It also appears to inhibit the enzymes sucrase and maltase to a greater extent than does acarbose. It does not undergo metabolism and is renally excreted unchanged.
Gastrointestinal disturbances (loose stools, flatu-lence, and abdominal cramping) are the most frequently observed side effects of the α-Glucosidase inhibitors. These effects can be minimized by starting patients on a low dose and then slowly advancing the dose as toler-ance develops; curtailment of carbohydrate consump-tion also can alleviate these effects. Patients should be counseled that these side effects will occur and that tol-erance should develop; otherwise, compliance will be low and about one-third of patients will stop their med-ication. Unlike the sulfonylureas, insulin, and the thia-zolidinediones, α-Glucosidase inhibitors do not cause weight gain. Insulin levels do not change in the presence of α-Glucosidase inhibitors, so fasting hypoglycemia does not occur when α-Glucosidase inhibitors are used as monotherapy. Although the α-Glucosidase inhibitors may be used as monotherapy, they are usually used in combination with metformin, sulfonylureas, or insulin. Under the best circumstances, α-Glucosidase inhibitors can be expected to promote a 0.5 to 1% reduction in a patient’s hemoglobin A1c. Leaving aside their gastroin-testinal side effects, α-Glucosidase inhibitors appear to be relatively safe.