Dosing of metformin The recommended dose for metformin is shown in Table 1. Metformin is typically initiated at a dose of 500 mg once daily. The dose is commonly titrated up by 500 mg every week as tolerated, to a typical goal dosage of 1,000 mg twice daily. While Table 1: Noninsulin Antihyperglycemic Agents: Biguanides Biguanide
2,500 mg is the maximum dose of metformin, most healthcare providers will prescribe up to 2,000 mg daily because increasing the dose from 2,000 to 2,500 mg has minimal impact on A1C (Baker et al., 2021; Odegard & Capoccia, 2022).
Available Strengths
Starting Dose
How to Titrate Dose
Dosage Range
Generic Name (Trade Name) Metformin Glucophage)
• 500 mg • 850 mg • 1,000 mg
• Starting dose of 500 mg/day with largest meal of the day. • Starting dose of 500 mg/day with largest meal of the day.
• Titrate in increments of 1 tablet (500 mg) each week up to a maximum of 2,000 mg/daily. • May take 4–6 weeks to see full effect. • Titrate in increments of 1 tablet (500 mg) each week up to a maximum of 2,000 mg/daily. • May take 4–6 weeks to see full effect.
• Maximum dose of
2,500 mg/day, given in divided doses.
Meformin XR (Glucophage XR)
• Glucophage XR:
• Maximum dose of
2,500 mg/day, given in divided doses.
○ 500 mg ○ 750 mg
(Fortamet) (Glumetza)
Metformin Hydrochloride (Riomet)
• 500 mg/5 mL
• 500 mg (5 mL) orally twice a day.
• 500 mg (5 mL) weekly or 850 mg (8.5 mL) every 2 weeks.
• Maximum dose of 2,550 mg (25.5 mL) per day, given in divided doses.
Key points for patients taking metformin: ● Take metformin with food to minimize side effects. ● Extended-release tablets may have fewer GI side effects than immediate-release tablets. ● GI side effects are often dose dependent; decrease dose to find acceptable tolerability. ● Metformin is likely to be stopped during hospitalizations and with procedures that require injection of dye.
Self-Assessment Quiz Question #1 Which of the following noninsulin antihyperglycemic agent is considered first-line therapy for newly diagnosed patients with type 2 diabetes when the goal is to achieve and maintain glycemic control? a. Glipizide.
b. Glimepiride. c. Glucophage. d. Glyburide.
SULFONYLUREAS
Sulfonylureas are sometimes referred to as insulin secretagogues. These agents work by stimulating the release of insulin from pancreatic beta cells. Sulfonylureas were first discovered in 1942 and at that time were the only no-insulin antihyperglycemic medications available. With the introduction of newer antihyperglycemic agents, the use of sulfonylureas has dropped considerably. However, using sulfonylureas is important in managing patients with type 2 diabetes when pancreatic beta cells continue to produce enough insulin. The first sulfonylurea agents were introduced in the U.S. around 1956 and are referred to as first-generation agents. These agents are no longer prescribed because of prolonged hypoglycemic effects. In the mid-1980s, second-generation sulfonylureas, including glyburide (DiaBeta; Micronase), glipizide (Glucotrol), and glimepiride (Amaryl), were introduced in the U.S. Second-generation sulfonylureas are not first-line drugs for treating patients with type 2 diabetes but may be added as a second or third drug when monotherapy fails (Dang, 2017; Sisson & Zimmerman, 2017). Glyburide has a longer duration of action than glipizide (Glucotrol, Glucotrol XL) and is more likely Mechanism of action Use of sulfonylureas requires a functioning pancreas. Sulfonylureas bind to and inhibit adenosine triphosphate (ATP) synthesis, blocking the inflow of potassium (K+) through the ATP channel. This depolarizes pancreatic beta-cell membranes, causing calcium channels to open and an influx of calcium ions, which stimulates insulin secretion from the pancreatic beta cells (Sola et al., 2015). Other extrapancreatic effects associated with
to cause hypoglycemia (Sola et al., 2015). Glipizide (Glucotrol, Glucotrol XL) is considered an intermediate-acting second- generation sulfonylurea with a duration of action between 12 and 24 hours. An extended-release form of glipizide (Glucotrol XL) is available. Although a maximum dose of 40 mg/daily is approved, there is a little additional glucose-lowering effect beyond 20 mg/daily (White, 2022). With the arrival of new noninsulin antihyperglycemic agents, like glucagon-like peptide-1 receptor agonists (GLP-1 RA), dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose cotransporter 2 (SGLT2) inhibitors, there are healthcare providers who believe newer agents have replaced sulfonylureas. However, other healthcare providers believe using sulfonylureas is appropriate when particular attention is paid to the risk of hypoglycemia, weight gain is not a concern, or if cost is an issue (Scheen, 2021). The American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) recommend the use of sulfonylureas as a last choice of medication (Davies et al., 2022).
sulfonylureas include lowering serum blood glucose levels by decreasing insulin metabolism in the liver, decreasing glucagon secretion, and increasing sensitivity to insulin in peripheral tissue (Kroon & Zhou, 2022a; Sola et al., 2015). Such extrapancreatic effects are the result of improved glycemic variability, which then reduces glucose toxicity (Kroon & Zhou, 2022a).
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