Metformin (Glucophage) Reactions

Metformin (Glucophage) is available in the Pakistan since 1998. It falls in the same drug class as phenformin. Metformin is considered a first line agent and is significantly useful in people with known insulin resistance

GLUCOPHAGE® (metformin hydrochloride tablets) and GLUCOPHAGE® XR (metformin hydrochloride extended-release tablets) are oral antihyperglycemic drugs used in the management of type 2 diabetes. Metformin hydrochloride (N,N-dimethylimidodicarbonimidic diamide hydrochloride) is not chemically or pharmacologically related to any other classes of oral antihyperglycemic agents. The structural formula is as shown:

Glucophage (metformin hydrochloride tablets) Structural Formula Illustration

Metformin hydrochloride is a white to off-white crystalline compound with a molecular formula of C4H11N5 • HCl and a molecular weight of 165.63.

Metformin improves hyperglycemia primarily through its suppression of hepatic glucose production, especially hepatic gluconeogenesis[1]. The “average” person with type 2 diabetes has three times the normal rate of gluconeogenesis; metformin treatment reduces this by over one third.[2] Metformin activates AMP-activated protein kinase (AMPK), a liver enzyme that plays an important role in insulin signaling, whole body energy balance, and the metabolism of glucose and fats;[3] activation of AMPK is required for metformin’s inhibitory effect on the production of glucose by liver cells.[4] Research published in 2008 further elucidated metformin’s mechanism of action, showing that activation of AMPK is required for an increase in the expression of SHP (Small heterodimer partner), which in turn inhibits the expression of the hepatic gluconeogenic genes PEPCK and Glc-6-Pase.[5] Metformin is frequently used in research along with AICAR as an AMPK agonist. The mechanism by which biguanides increase the activity of AMPK remains uncertain; however, research suggests that metformin increases the amount of cytosolic AMP (as opposed to a change in total AMP or total AMP/ATP).[6]

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In addition to suppressing hepatic glucose production, metformin increases insulin sensitivity, enhances peripheral glucose uptake, decreases fatty acid oxidation, and decreases absorption of glucose from the gastrointestinal tract.[8] Increased peripheral utilization of glucose may be due to improved insulin binding to insulin receptors.[9] AMPK probably also plays a role, as metformin administration increases AMPK activity in skeletal muscle.[10] AMPK is known to cause GLUT4 translocation, resulting in insulin-independent glucose uptake. Some metabolic actions of metformin do appear to occur by AMPK-independent mechanisms; a recent study found that “the metabolic actions of metformin in the heart muscle can occur independent of changes in AMPK activity and may be mediated by p38 MAPK- and PKC-dependent mechanisms.”[11]

Metformin causes a few gastrointestinal side effects including nausea, metallic taste, diarrhea and abdominal discomfort[7] . These can be avoided if the dose is increased slowly, and taking the drug with meals. A small amount of weight loss, possibly due to drop in net caloric intake due to appetite repression and/or a reduction in hyperinsulinemia is suggested. Falling in the same drug class as phenformin, the reported incidence of lactic acidosis is surprisingly low, 0.03 per 1000.

In a US double-blind clinical study of GLUCOPHAGE in patients with type 2 diabetes, a total of 141 patients received GLUCOPHAGE therapy (up to 2550 mg per day) and 145 patients received placebo.

Most Common Adverse Reactions (>5.0 Percent) in a Placebo-Controlled Clinical Study of GLUCOPHAGE Monotherapy

The occurrence can further be avoided if contraindications are followed. It is contraindicated in people with a high risk of lactic acidosis: renal serum creatinine levels over 150 μmol/l[14}or hepatic impairment, respiratory insufficiency, severe infection and alcohol abuse. Any pharmacological therapy that alters either of the factors mentioned before is also considered. It should also be used cautiously in elderly especially those above 80 years of age. It is recommended to monitor renal function upon initiation and at least once a year thereafter.

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It should be withheld immediately before a person has a procedure with a radiocontrast dye, as the dye increases the risk of renal failure and therefore lactic acidosis [15] [16]. It should also be discontinued before and surgery and can be started immediately after if the renal function is normal and the patient is stable. It is also recommended to monitor hematological parameters as it alters vitamin B12 absorption [12] [13] and therefore cause anemia (7% in clinical trials). The mechanism of action is unknown but can be reversed by discontinuation of the drug.

Daily dosage should be 500 mg orally twice daily with meals. The dose can be increased every 2 weeks to 2000 mg daily.

References

1. Kirpichnikov D, McFarlane SI, Sowers JR (2002). “Metformin: an update”. Ann Intern Med 137 (1): 25-33. PMID 12093242.
2. Hundal R, Krssak M, Dufour S, Laurent D, Lebon V, Chandramouli V, Inzucchi S, Schumann W, Petersen K, Landau B, Shulman G (2000). “Mechanism by which metformin reduces glucose production in type 2 diabetes” (PDF). Diabetes 49 (12): 2063-9. doi:10.2337/diabetes.49.12.2063. PMID 11118008.
3. Towler MC, Hardie DG (2007). “AMP-activated protein kinase in metabolic control and insulin signaling”. Circ Res 100 (3): 328-41. doi:10.1161/01.RES.0000256090.42690.05. PMID 17307971.
4. Zhou G, Myers R, Li Y, Chen Y, Shen X, Fenyk-Melody J, Wu M, Ventre J, Doebber T, Fujii N, Musi N, Hirshman M, Goodyear L, Moller D (2001). “Role of AMP-activated protein kinase in mechanism of metformin action”. J Clin Invest 108 (8): 1167-74. doi:10.1172/JCI13505. PMID 11602624.
5. Kim YD, Park KG, Lee YS, et al. (2008). “Metformin inhibits hepatic gluconeogenesis through AMP-activated protein kinase-dependent regulation of the orphan nuclear receptor SHP”. Diabetes 57 (2): 306-14. doi:10.2337/db07-0381. PMID 17909097.
6. Zhang L, He H, Balschi JA (2007). “Metformin and phenformin activate AMP-activated protein kinase in the heart by increasing cytosolic AMP concentration”. Am J Physiol Heart Circ Physiol 293 (1): H457-66. doi:10.1152/ajpheart.00002.2007. PMID 17369473.
7. Bolen S, Feldman L, Vassy J, et al (2007). “Systematic review: comparative effectiveness and safety of oral medications for type 2 diabetes mellitus”. Ann Intern Med 147 (6): 386-99. PMID 17638715.
8. Royal Pharmaceutical Society of Great Britain and the British Medical Association. “Chapter 6:Endocrine system—6.1.2.2 Biguanides”, British National Formulary, 54.
9. Bailey CJ, Turner RC (1996). “Metformin”. N Engl J Med 334 (9): 574-9. doi:10.1056/NEJM199602293340906. PMID 8569826.
10. Musi N, Hirshman MF, Nygren J, et al. (2002). “Metformin increases AMP-activated protein kinase activity in skeletal muscle of subjects with type 2 diabetes”. Diabetes 51 (7): 2074-81. PMID 12086935.
11. Saeedi R, Parsons HL, Wambolt RB, et al. (2008). “Metabolic actions of metformin in the heart can occur by AMPK-independent mechanisms”. Am J Physiol Heart Circ Physiol 294 (6): H2497-506. doi:10.1152/ajpheart.00873.2007. PMID 18375721
12. Andrès E, Noel E, Goichot B (2002). “Metformin-associated vitamin B12 deficiency”. Arch Intern Med 162 (19): 2251-2. doi:10.1001/archinte.162.19.2251-a. PMID 12390080.
13. Gilligan M (2002). “Metformin and vitamin B12 deficiency”. Arch Intern Med 162 (4): 484-5. doi:10.1001/archinte.162.4.484. PMID 11863489
14. Jones G, Macklin J, Alexander W (2003). “Contraindications to the use of metformin”. BMJ 326 (7379): 4-5. doi:10.1136/bmj.326.7379.4. PMID 12511434
15. Weir J (March 19, 1999). Guidelines with Regard to Metformin-Induced Lactic Acidosis and X-ray Contrast Medium Agents. Royal College of Radiologists. Retrieved on 2007-10-26 through the Internet Archive.
16. a b Thomsen HS, Morcos SK (2003). “Contrast media and the kidney: European Society of Urogenital Radiology (ESUR) guidelines”. Br J Radiol 76 (908): 513-8. doi:10.1259/bjr/26964464. PMID 12893691.