Oral hypoglycemic drugs lower blood glucose level and are effective orally, unlike insulin which must be given by injection (mainly by subcutaneous injection and in emergencies by intravenous injection) which is the major drawback of insulin. Due to the drawback of insulin (must be given by injection) orally effective drugs in diabetes have always been searched.

In the early 1940s, it was noticed that antibiotics sulfonamides have hypoglycemia as side effect and taking this as lead the first orally acting drug which can lower blood sugar level, tolbutamide was introduced in 1957 and subsequently many other drugs followed and by 1970s many oral hypoglycemic drugs were available for better management of type-2 diabetes.

At present there are five different classes of oral hypoglycemic agents which are used commonly. Each class has distinct and unique pharmacologic properties. These drugs are used if diet and exercise do not provide adequate blood glucose control. They are used either alone or in combination of 2 or more different groups (class) of oral hypoglycemic drugs.

1. Sulfonylureas.

2. Biguanides.

3. Meglitinides or phenylalanine analogues.

4. Thiazolidinediones.

5. Alpha-glucosidase inhibitors.

(1) Sulfonylureas:

Sulfonylureas are again subdivided into (a) first generation and (b) second generation sulfonylureas.

The first generation sulfonylureas are:

• Tolbutamide.
• Tolazamide
• Chlorpropamide.

The first generation sulfonylureas are very rarely used nowadays, due to higher side effects (such as frequent drug interactions), lesser effectiveness (at maximum doses, first-generation sulfonylureas have similar potency as second-generation agents) and availability of better effective second generation sulfonylureas with lesser side effect profile.

Second generation sulfonylureas are:

• Glimepiride.
• Glipizide and Glipizide (extended release).
• Gliclazide.
• Glyburide and Glyburide (micronized)
• Glibenclamide.

These are very commonly used for treatment of type-2 diabetes.

(2) Biguanides:

There are only 2 (Two) different biguanides:

• Phenformin (due to high incidence of side effects such as lactic acidosis, phenformin is banned in most countries and not available at present).
• Metformin (very commonly prescribed oral hypoglycemic agent, especially in obese diabetics).

(3) Meglitinides or phenylalanine analogues:

They are recently developed and are quick and short acting.

• Repaglinide.
• Nateglinide.

(4) Thiazolidinediones:

• Rosiglitazone.
• Pioglitazone.

(5) Alpha-glucosidase inhibitors:

• Acarbose.
• Miglitol.

Other drugs used in diabetes:

Guargum, glucomannan etc. are agents, which can be used in diabetes in some cases as adjunct to oral hypoglycemic drugs, especially to reduce the dose of oral hypoglycemic drugs as well as in conjunction with diet.