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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.D. [2]

Overview

Anti-diabetic drugs treat diabetes mellitus by lowering glucose levels in the blood. With the exceptions of insulin, exenatide, and pramlintide, all are administered orally and are thus also called oral hypoglycemic agents or oral antihyperglycemic agents. There are different classes of anti-diabetic drugs, and their selection depends on the nature of the diabetes, age and situation of the person, as well as other factors. Diabetes mellitus type 1 is a disease caused by the lack of insulin. Insulin must be used in Type I, which must be injected or inhaled. Diabetes mellitus type 2 is a disease of insulin resistance by cells. Treatments include (1) agents which increase the amount of insulin secreted by the pancreas, (2) agents which increase the sensitivity of target organs to insulin, and (3) agents which decrease the rate at which glucose is absorbed from the gastrointestinal tract. Several groups of drugs, mostly given by mouth, are effective in Type II, often in combination. The therapeutic combination in Type II may include insulin, not necessarily because oral agents have failed completely, but in search of a desired combination of effects. The great advantage of injected insulin in Type II is that a well-educated patient can adjust the dose, or even take additional doses, when blood glucose levels measured by the patient, usually with a simple meter, as needed by the measured amount of sugar in the blood.

Oral hypoglycemic agents

Drug	Class	Mechanism of action	Dosage	Side effects
Tolbutamide (Ornase) Tolazamide (Tolinase), Chlorpropamide (Diabenese)	Sulfonylureas (1st generation)	Increases insulin production in the pancreas	Tolbutamide: 0.25–2.0 g/day in divided doses; maximum, 3 g/day, Tolazamide: 100–1,000 mg/day in divided doses; maximum, 1 g/day, Chlorpropamide: 100–500 mg/day BID; maximum, 750 mg/day	Hypoglycemia, weight gain, hyperinsulinemia, Disulfiram reaction with alcohol, long acting extreme caution with elderly or patients with hepatic or renal dysfunction, periodic evaluation of liver function is suggested
Glyburide (Micronase, Diabeta,Glynase), Glipizide (Glucotrol, Glucotrol XL), Glimepiride (Amaryl)	Sulfonylureas (2nd generation)	Increases insulin production in the pancreas	Glyburide: 1.25–5 mg/once or twice a day; maximum, 20 mg/day, Glynase: 0.75–12.0 mg/day; maximum 12 mg/day, Glipizide: 2.5–20.0 mg/OD or BID; maximum, 40 mg/day; or XL 2.5–10.0 mg/OD or BID; maximum, 20 mg/day, Glimepiride: 1–8 mg/day; maximum, 8 mg/day	Hypoglycemia, weight gain,hyperinsulinemia, caution in patients with hepatic or renal impairment, Glipizide preferred in renal impairment, Glimepiride indicated for use with insulin, Shown to have some insulin-sensitizing effect
Repaglinide (Prandin)	Meglitinide	Increases insulin release from pancreas	New diagnosis or A1C <8%, 0.5 mg; A1C >8%, 1–2 mg, 15–30 min before each meal; increase weekly until results are obtained; maximum, 16 mg/day	Hypoglycemia, weight gain,hyperinsulinemia caution on patient with hepatic or renal impairment, medication no more than 30 minutes prior to a meal. If meals are skipped or added, the medication should be skipped or added as well. Approved for use as monotherapy or in combinatin with TZD or metformin.
Nateglinide (Starlix)	Phenylalanine derivative	Increases insulin release from pancreas	60–120 mg before each meal	Minimal risk of hypoglycemia, use with caution in moderate to severe hepatic disease, approved as monotherapy or in combination with metformin or TZD, 2-hour duration of action
Metformin (Fortamet,Glumetza, Glucophage)	Biguanide	Decreases hepatic glucose production, minor increase in muscle glucose uptake which may improve insulin resistance	500 mg/day BID with meals, increase by 500 mg every 1–3 wk, BID or TID; usually most effective at 2,000 mg/day; maximum, 2,550 mg/day Long acting form Glucophage XR: 500mg OD, max dose 2000 mg OD	Nausea, diarrhea, metallic taste, lactic acidosis, cautious in alcohol abuse, liver or kidney disease, CHF, contraindicated if serum creatinine is: >1.5 mg/dL in men or >1.4 mg/dL women, monitor hematological and renal function annually, discontinue for 48 hr after contrast dye procedures, beneficial in obese patients as help in weight loss, improved lipid profile, and lack of potential for hypoglycemia
Rosiglitazone (Avandia)	Thiazolidinedione	Decreases insulin resistance, increasing glucose uptake, fat redistribution; minor decrease in hepatic glucose output; preserves cell function; decreases vascular inflammation	Initially 4 mg/day in single or divided doses, increase to 8 mg/day in 12 wk, if needed; maximum, 8 mg/day with or without food	Minor weight increase of 3–6 lbs., edema, contraindicated in CHF or hepatic disease, avoid initiation if ALT >2.5X upper limit of normal, approved for use as monotherapy and in combination with metformin, sulfonylureas, or insulin, Less interactions associated with CYP-450
Pioglitazone (Actos)	Thiazolidinedione	same as rosiglitazone	Initially 15 or 30 mg/day; maximum with or without food 45 mg for monotherapy,30 mg for combination therapy

Insulin

Insulin is usually given subcutaneously, either by injections or by an insulin pump. Research is underway of other routes of administration. In acute care settings, insulin may also be given intravenously. There are several types of insulin, characterized by the rate which they are metabolized by the body.

Sulfonylureas

• Sulfonylureas were the first widely used oral hypoglycemic medications. They are insulin secretagogues, triggering insulin release by direct action on the K_ATP channel of the pancreatic beta cells.
• The "second-generation" drugs are now more commonly used. They are more effective than first-generation drugs and have fewer side effects.
• Sulfonylureas bind strongly to plasma proteins. Sulfonylureas are only useful in Type II diabetes, as they work by stimulating endogenous release of insulin.
• They work best with patients over 40 years old, who have had diabetes mellitus for under ten years. They can not be used with type I diabetes, or diabetes of pregnancy. They can be safely used with metformin or -glitazones.

Meglitinides

• Meglitinides help the pancreas produce insulin and are often called "short-acting secretagogues."
• Their mode of action is original, affecting potassium channels. By closing the potassium channels of the pancreatic beta cells, they open the calcium channels, hence enhancing insulin secretion.
• They are taken with meals to boost the insulin response to each meal.

Biguanides

• Biguanides reduce hepatic glucose output and increase uptake of glucose by the periphery, including skeletal muscle.
• Metformin should be temporarily discontinued before any radiographic procedure involving intravenous iodinated contrast as patients are at an increased risk of lactic acidosis.

Thiazolidinediones

• Thiazolidinediones (TZDs), also known as "glitazones," bind to PPARγ, a type of nuclear regulatory proteins involved in transcription of genes regulating glucose and fat metabolism.
• These PPARs act on Peroxysome Proliferator Responsive Elements (PPRE [3]). The PPREs influence insulin sensitive genes, which enhance production of mRNAs of insulin dependent enzymes. The final result is better use of glucose by the cells.
• As a result of multiple retrospective studies, there is a concern about rosiglitazone's safety, although it is established that the group, as a whole, has beneficial effects on diabetes. The greatest concern is an increase in the number of severe cardiac events in patients taking it. The ADOPT study showed that initial therapy with drugs of this type may prevent the progression of disease, as did the DREAM trial.

• Concerns about the safety of rosiglitazone arose when a retrospective meta-analysis was published in the New England Journal of Medicine. There have been a significant number of publications since then, and a Food and Drug Administration panel voted, with some controversy, 20:3 that available studies "supported a signal of harm," but voted 22:1 to keep the drug on the market. Safety studies are continuing.
• In contrast, at least one large prospective study, PROactive 05, has shown that pioglitazone may decrease the overall incidence of cardiac events in people with type II diabetes who have already had a heart attack.

Alpha-glucosidase inhibitors

Alpha-glucosidase inhibitors are "diabetes pills" but not technically hypoglycemic agents because they do not have a direct effect on insulin secretion or sensitivity. These agents slow the digestion of starch in the small intestine, so that glucose from the starch of a meal enters the bloodstream more slowly, and can be matched more effectively by an impaired insulin response or sensitivity. These agents are effective by themselves only in the earliest stages of impaired glucose tolerance, but can be helpful in combination with other agents in type 2 diabetes.

• miglitol (Glyset)
• acarbose (Precose/Glucobay)

These medications are rarely used in the United States because of the severity of their side effects (flatulence and bloating). They are more commonly prescribed in Europe.

They do have the potential to cause weight loss by lowering the amount of sugar metabolized.

Peptide analogs

File:Incretins and DPP 4 inhibitors.svg

Overview of insulin secretion

Incretin mimetics

Incretins are insulin secretagogues. The two main candidate molecules that fulfill criteria for being an incretin are Glucagon-like peptide-1 (GLP-1) and Gastric inhibitory peptide (aka glucose-dependent Insulinotropic peptide or GIP). Both GLP-1 and GIP are rapidly inactivated by the enzyme dipeptidyl peptidase-4 (DPP-4).

Glucagon-like peptide (GLP) analogs

GLP agonists bind to a membrane GLP receptor. As a consequence of this, insulin release from the pancreatic beta cells is increased. Endogenous GLP has a half life of only a few minutes; thus an analogue of GLP would not be practical.

• Exenatide (also Exendin-4, marketed as Byetta) is the first GLP agonist approved for the treatment of type 2 diabetes. Exenatide is not an analogue of GLP, but rather a GLP agonist. Exenatide has only 53% homology with GLP, which increases its resistance to degradation by DPP-4 and extends its half-life.
• Liraglutide- a once daily human analogue (97% homology) is being developed by Novo Nordisk. As of 2007, it is in phase III clinical trials.

These agents may also cause a decrease in gastric motility, responsible for the common side effect of nausea, and is probably the mechanism by which weight loss occurs.

Gastric inhibitory peptide (GIP) analogs

• None are FDA approved

DPP-4 inhibitors

Dipeptidyl peptidase-4 (DPP-4) inhibitors increase blood concentration of the incretin GLP-1 (glucagon-like peptide-1) by inhibiting its degradation by dipeptidyl peptidase-4 (DPP-4). Examples are:

• vildagliptin
• sitagliptin

Amylin analogues

Amylin agonist analogues slow gastric emptying and suppress glucagon. As of 2007, pramlintide is the only clinically available amylin analogue. Like insulin, it is administered by subcutaneous injection. The most frequent and severe adverse effect of pramlintide is nausea, which occurs mostly at the beginning of treatment and gradually reduces.

Experimental agents

Many other potential drugs are currently in investigation by pharmaceutical companies. Some of these are simply newer members of one of the above classes, but some work by novel mechanisms. For example, at least one compound that enhances the sensitivity of glucokinase to rising glucose is in the stage of animal research. Others are undergoing phase I/II studies.

• PPARα/γ ligands (muraglitazar and tesaglitazar) - development stopped due to adverse risk profile
• SGLT (sodium-dependent glucose transporter 1) inhibitors increase urinary glucose.
• FBPase (fructose 1,6-bisphosphatase) inhibitors decrease gluconeogenesis in the liver.

Herbal extracts

The first registered use of anti-diabetic drugs was as herbal extracts used by Indians in the Amazon Basin for the treatment of type 2 diabetes, and today promoted as vegetable insulin although not formally an insulin analog. The major recent development was done in Brazil around Myrcia sphaerocarpa and other Myrcia species.

"Many countries, especially in the developing world, have a long history of the use of herbal remedies in diabetes (...) STZ diabetic rats were also used to test Myrcia Uniflora extracts (...) ".

The usual treatment is with concentrated (root) Myrcia extracts, commercialized in a 4 US dollar per kilogram packed rocks (~100 times cheaper than equivalent artificial drugs), named "Pedra hume de kaá". Phytochemical analysis of the Myrcia extracts reported kinds of flavanone glucosides (myrciacitrins) and acetophenone glucosides (myrciaphenones), and inhibitory activities on aldose reductase and alpha-glucosidase.

A recent review article presents the profiles of plants with hypoglycaemic properties, reported in the literature from 1990 to 2000 and states that "Medical plants play an important role in the management of diabetes mellitus especially in developing countries where resources are meager."

External links

ndep.nih.gov drug tables

Sources

• Lebovitz, Harold E. (2004). Therapy For Diabetes Mellitus and Related Disorders, 4^th ed., Alexandria, VA: American Diabetes Association. ISBN 1-58040-187-2. 
• Adams, Michael Ian; Holland, Norman Norwood (2003). Core Concepts in Pharmacology. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-089329-3. ar:مضادات السكري