INTRODUCTION:

Galega officinalis is a summer-flowering perennial herb found in most temperate regions (1,2). This plant is also called as goat’s rue, false indigo, professor weed, French lilac, Spanish sanfoin, and Italian fitch. One of the first use of this herb was to cure the frequent urination associated with the disease now called as diabetes mellitus. The plant was equally used in cows as was in humans. It helped to stimulate lactation in cows. Due to the plant’s side effects, its widespread use was restricted (1).

Early experiments with Galega officinalis:

Muller and Reinwein had an early clinical experience with galegine sulphate, an active ingredient of Galega officinalis. Following a self-administration of 109 mg galegine sulphate, blood glucose levels were assessed for 25 hours. This study had then expatiated to healthy individuals and later on to a diabetic population. In all three subjects, the results were similar, i.e., a hypoglycaemic effect was seen in all the cases (3).

Eusebio Garcia, a specialist in infectious diseases, treated patients suffering from an endemic. In 1949, Garcia discovered a “new synthetic” drug called flumamine. After treating the patients with flumamine, Garcia reported a relief of headache and cure in virtually 30 patients within 24 hours. Garcia stated that flumamine is similar to polymethethylene diguanides, it has biguanide groups. Garcia stated further that flumamine has the property to lower blood sugar, however, there was no proven evidence (3).

In 1926, polymethethylene diguanides had been introduced for the treatment of diabetes. The existence of this drug did not last for long. Due to its debilitating effect on the liver, it had been withdrawn in the 1940s. In 1957, Jean Sterne, a specializing physician in diabetes, worked with galegine. Sterne decided to do research on flumamine after Garcia’s discovery, that it reduced blood sugar concentrations. Sterne stated that flumamine had a powerful hypoglycemic effect and its chronic toxicity was practically nil, there were no growth deterioration and there were no decreased hepatic function (3).

Afterwards, formamine, soon renamed as metformin, showed an immense advantage over insulin for treating type 2 diabetes mellitus. Although Sterne’s study proved hypoglycaemic effects, it was still doubtful among many. The study that followed had taken place in 1962. A total of 39 patients were involved, where 37 were aged over 30, out of which 28 were over 50 years of age. The study concluded the following (3):

· 14 showed satisfactory control of disease with metformin.

· 6 showed improvement if metformin was combined with low dose insulin or any other oral antidiabetic agents.

· Type 1 diabetes did not respond to the treatment.

· Treatment was with 1-3 g of metformin per day, given as three divided doses.

Chemical Synthesis:

On working with dicyanodiamide and dimethylammonium, Dublin chemists, Emil Werner and James Bell had discovered a compound in 1922. They found out that dicyanodiamide on reaction with dimethyl ammonium chloride yielded dimethyldiguanide, i.e., metformin. But the chemists did not realize the pharmaceutical value of the drug they had discovered (3).

Structure of Metformin:

Metformin:

Metformin is a biguanide with a guanidine and galegine connection.

Guanidine:

Galegine:

FDA and non FDA uses:

FDA uses are those indications of drugs that are approved by the US government. The Food and Drugs Administration approves metformin to be used for the treatment of Type 2 Diabetes Mellitus (4). Although metformin was initially proven to treat high sugar levels, there are many uses of metformin proven to be effective. Majority of the uses have not been approved by the FDA, but are used widely by the doctors. This is called off label use (5).

The non FDA uses are those that can be used for a condition that is not approved by the FDA, but have been proved to be effective. Doctors around the globe prescribe metformin not only for diabetes, but also for gestational diabetes mellitus, obesity, hypersecretion of ovarian androgens, polycystic ovary syndrome (PCOS), antipsychotic therapy induced weight gain, cancer treatment and anti-aging (6). Metformin was approved for treatment of Type 2 Diabetes Mellitus in 1958 for UK, 1972 for Canada and 1995 by FDA in USA (6).

Type 2 Diabetes Mellitus:

Diabetes mellitus is routinely used as the term for raised blood sugar levels. Type 2 diabetes mellitus is a chronic metabolic condition. The body loses the ability to use insulin the way it should. The ability to produce insulin also decreases the reason for high blood glucose levels (7).

In 2012, 29.1 million Americans were diagnosed with type 2 diabetes mellitus. In the same year, researches showed that almost 85-90% of all cases were diagnosed diabetes mellitus. In 2013, it was estimated that 90% adults were diagnosed with type 2 diabetes mellitus. It was found that type 2 diabetes mellitus was more common among Caucasians, particularly African, Caribbean and South Asian family origin. This was said to occur in all age groups, whereas a study in 2012 proved it was more common in patients aged 65 and above. Moreover, is increasingly being diagnosed in children (7).

Type 2 diabetes mellitus may be due to peripheral insulin resistance, impaired regulation of hepatic glucose production, declining β-cell function which leads to β-cell failure. Glucose transport in β-cells dramatically reduces. This causes shift in the control point for insulin secretion from glucokinase to glucose transport system. As the disease progresses, the synthesis of insulin becomes impaired, i.e., desensitization of β-cells. The accumulation of glycogen in the β-cells can be explained by the paradoxical inhibitory effect of insulin due to glucose. The risk of getting type 2 diabetes mellitus in family is attributed in impairment in first phase insulin secretion (8).

Metformin, being the biguanide class is the drug of choice for patients who are obese and have type 2 diabetes mellitus. It is used in case of insulin resistance. Metformin works by decreasing hepatic glucose production and decreasing peripheral insulin resistance. Metformin causes the glucose transporters to shift or transfer from microsomes of hepatic and muscle cells to the plasma membrane (9).

A great boon about metformin is that it does not cause weight gain. More importantly, metformin causes a decrease in the lipid profile. There are reduced total and very low density lipoprotein triglycerides, total cholesterol and very low density cholesterol levels. High density lipoproteins also increase (10). The usual dose of metformin is 500 mg three or four times a day or 850 mg two or three times a day. Maximum dose should not exceed 2.55 g per day. Metformin tablets are taken with food to avoid gastric intolerance. In case any dose is missed, the missed dose is taken the next day at the usual time. Doubling the dose is entirely discouraged. Overdose occurs after ingestion of metformin in amounts more than 50 g (10).

The expected adverse reactions of metformin include epigastric discomfort, nausea and vomiting, diarrhoea, drowsiness, weakness, dizziness, malaise and headache. Hypoglycemia is found to be in 10% of patients, while lactic acidosis is found in 32%. For patients suspected with metformin overdose, hemodialysis is useful for removal of the accumulated drug (10).

In patients with renal impairment, dose modification is essential. Metformin is excreted through kidneys. The accumulation of metformin and lactic acidosis increases with progression of impairment of kidneys. Before the initiation of the treatment with metformin, obtaining eGFR is crucial. In patients with eGFR < 30 ml/min/1.73 m², use of metformin is contraindicated. If the eGFR is 30-45 ml/min/1.73m², it is not recommended. Renal function reduces with increase in age. So, for the geriatric population, it is advised to carefully titrate metformin so as to achieve the minimum dose with adequate glycemic effect. In elderly patients, the renal function should be checked regularly and dose is not to be titrated till maximum. Once metformin has been started, renal function should be assessed every 6 months. It is very important that the renal function remains normal. Metformin is not administered to those patients whose renal function is impaired. In case of renal dysfunction, the renal function is monitored on a more frequent regular basis. The laboratory tests or lab tests required during metformin therapy is fasting blood glucose and glycosylated haemoglobin. Glycosylated haemoglobin should be checked on long term control (10).

Gestational Diabetes Mellitus:

Women may suffer from diabetes mellitus either before pregnancy or during pregnancy, the former being type 2 diabetes mellitus while the latter being gestational diabetes mellitus. Gestational diabetes mellitus starts from the 24^th week of pregnancy. Several studies have been carried out to prove the hypoglycaemic effect of metformin in gestational diabetes mellitus (6).

The MiG (Metformin in Gestational diabetes 2008) trial has proved that metformin was found safe and effective. National Diabetes Guidelines (NICE) and the British National Formulary say that metformin can be used in pregnancy. As metformin is excreted through kidneys, it is safe to continue metformin while breastfeeding. Metformin, alone or with supplemental insulin, was not associated with increased perinatal complications as compared with insulin (9).

The starting dose of metformin for gestational diabetes mellitus is 500 mg, with or after a meal. This will then soon be increased by another 500 mg. If the blood glucose levels are beyond a slight increase, the dose can be increased to 1 g with a main meal and then 1 g with another meal (9). If the patient was diabetic before pregnancy and on metformin, continuing metformin is acceptable (11).

Polycystic Ovary Syndrome (PCOS):

PCOS occurs in 15% of women which is an endocrine disorder characterized by menstrual irregularities, low fertility, obesity and high blood levels of male hormones in reproductive aged women (12). It is made up of three distinctive factors, hyperandrogenic state, anovulation and insulin resistance. PCOS confirms insulin resistance which leads to the assumption of a pre-diabetic state with glucose intolerance, gestational diabetes mellitus and overt diabetes. PCOS is also related to a list of comorbidities like type 2 diabetes mellitus, infertility, increased risk of cardiovascular diseases, physiological burden, etc (12).

Several studies show that insulin resistance stimulates the ovaries to produce male hormones, i.e., androgens. This causes stigmata of androgen excess such as hirsutism and acne. Metformin increases insulin sensitivity and furthermore, decreases the ovarian androgen production. This thereby normalizes the hormone levels, stabilizes menstrual irregularities and improves the fertility and ovulation. More to that, metformin helps mothers carry their baby to full term (13,14).

Mechanism of action of metformin is the activation of AMP-kinase pathway and causes a decrease in hepatic glucose production in metabolic pathway. It was observed that ovulation rates improved in women with PCOS by 46%. Obesity in patients exacerbated the metabolic and reproductive disorders associated with the syndrome. Hirsutism is less frequent in Asian patients (10%) as compared to Caucasian patients (70%) as defined by ethnicity (15).

Metformin is the drug of choice for the treatment of PCOS. For patients with metabolic syndrome and obesity, metformin is strongly recommended. Ameliorated symptoms were seen in patients taking metformin. Metformin improved the cardio metabolic profile. It also directly inhibits the androgen production. Metformin is chosen over oral contraceptives in patients where oral contraceptives were found to be ineffective or not recommended (13).

The usual dose of metformin for the treatment of PCOS is 1500-2500 mg per day. The initial dose of metformin is 250-500 mg per day and should be taken before the main meal. In case of any gastric troubles, abdominal discomfort, nausea, vomiting, diarrhoea or any such, doses are to be reduced, as these symptoms are dose dependent. During the course of treatment with metformin, monitoring of hepatic and renal functions are endorsed (15).

Hypersecretion of ovarian androgens:

Metformin is used for the treatment of hyperandrogenism and this fact is supported by a few studies. A study proved that metformin, 2250 mg per day ameliorated excess secretion of androgen in non-obese women with PCOS. In another study conducted by Yilmaz (15), decreased levels of testosterone and androgen were observed on the use of metformin (1700 mg per day). Nearly 30% decrease in hirsutism was observed in patients on taking 2250 mg per day metformin. A boost up of levels of androgens leads to hair growth in areas like a male (16).

OBESITY:

According to the World Health Organization, obesity and overweight are defined using the BMI. Body mass index (BMI) is defined as weight in kg divided by square of the height in meters (kg/m²). If BMI is over 25 kg/m² it is defined as overweight and if over 30 kg/m², is obese (17). Over the past decades, obesity has been a factor of concern. More than 60% of adults are either overweight or obese with BMI over 25 kg/m². Obesity can affect any person regardless of age, sex, ethnicity, etc (18).

Society has come to treatment methods for obesity. The foremost method of treatment for obesity is lifestyle interventions. This has been proven to decrease the BMI. For better effect and reduction in BMI, pharmacological methods have been used in addition to the lifestyle interventions (19). Out of the drugs available for the treatment of obesity, metformin happens to be one. Metformin was proven to be used for obesity and reduced BMI levels were observed. Metformin is one of drugs in a small spectrum of weight reducing drugs (19).

Metformin acts on obesity by causing a decrease in the appetite. Metformin contains a primary anorectic factor which reduces the appetite. Leptin levels were found to be decreased on taking metformin. Moreover, glucagon like peptide-1 levels rise significantly on taking metformin. This promotes weight loss. It was observed that adults with severe obesity lost weight more significantly than mildly obese patients (19). The dose of metformin given was 2500 mg per day. Insulin resistance may be a causative factor of abdominal obesity. Metformin improves the blood glucose control and thus provides less glucose for energy storage in adipose tissues (20). Many studies have resulted that the factor affecting metformin response is genetic variation. In a study, it was proven that metformin led to a weight loss by 2 kg and reduced chances of getting diabetes by 31% (21).

Medication induced weight gain:

Schizophrenia is a condition of concern among several people. It is evident through studies that the risk of weight gain, dyslipidemia and diabetes are high with the use of antipsychotics. Weight gain and abdominal adiposity which is directly associated with insulin resistance, dyslipidemia and risk of diabetes may be induced by second generation antipsychotics (22,23).

Out of the second generation antipsychotics, each differs in their tendency to produce weight gain, i.e., some may lead to more weight gain than others. The drugs causing the most weight gain are clozapine and olanzapine whereas quetiapine and risperidone cause weight gain by a slight lower degree and finally, ziprasidone and aripiprazole produce the least weight gain (24,25). Weight gain leads to decreased adherence to treatment. With decreased compliance, risk of psychotic relapse increases. Also with the increase in weight, risk for diabetes increases. With increased risk for diabetes and obesity, risk for cardiovascular disease increases. It was recently studied that more than two thirds of people with schizophrenia die from coronary artery disease. Stimulation of appetite, reducing physical activity and impairing metabolic regulation is the mechanism of antipsychotics induced weight gain (22,25).

In a study conducted in China on adults with schizophrenia, weight increased by 10% in the first year of treatment. The patients were then divided into 4 groups and treated accordingly. First group was treated only with metformin, 250 mg and three times a day. The second group was given placebo alone. The third group was lifestyle intervention with metformin. Lastly, the last group was lifestyle interventions with placebo. This study concluded that the best result was lifestyle modification with metformin. It had been proved that metformin had a superiority over lifestyle interventions and placebo in reducing weight (22). Serotonin and histamine antagonism results in craving of food and binge eating and thus increased weight (26).

Metformin in medication induced weight gain:

Metformin aids in weight loss. Drug induced weight gain can be reduced by metformin. Recommended dose of metformin is 250 mg three times daily. It assists in reduction of weight for those who gain 10% of body weight than pre-treatment (22). Metformin contains an anorectic factor and facilitates less hunger. This also aids in decreased appetite. Metformin causes decreased leptin levels, thus suppresses appetite. Metformin also increases the GLP-1 levels which enhances weight loss. Thus, metformin along with lifestyle changes is effective in the treatment of antipsychotics induced weight loss.

Cancer:

Although metformin is an oral hypoglycaemic agent, it is also used to inhibit cancer cell growth and proliferation. Metformin has been found to improve cancer prognosis. Several studies conclude that people with type 2 diabetes mellitus are also at a higher risk of developing cancer. The types of cancers that risk life in the presence of type 2 diabetes mellitus are cancer of pancreas, liver, endometrium, breast, colon, rectum and urinary bladder. Among the risks, cancer of liver, pancreas and endometrium are more prominent whereas cancers of the colon and rectum, breast and bladder are at a lower risk (27).

Certain risk factors remain common for both type 2 diabetes mellitus and cancer, few of them being age, sex, obesity, physical inactivity, diet, smoking and alcohol. Additionally, insulin resistance and hyper-insulinemia are independent risk factors for cancer development. Hyperglycemia related oxidative stress and accumulation of glycation end products increases risk of cancers as well (27). Studies have proven that metformin acts as a growth inhibitor instead of insulin sensitizer for epithelial cells. Research showed that the percentage of developing prostate cancer decreased by 34% in patients who took antidiabetic than those who did not (27).

In cancer cells, the mammalian target of rapamycin complex 1 (mTORC1) plays a major role. mTORC1 is associated with protein synthesis. Metformin helps in the inhibition of the mTORC1 pathway. Metformin also inhibits the growth of cancer cells through AMPK activation (28,29,30).

The other action of metformin is reduction of circulating levels of insulin and insulin like growth factor 1 (IGF-1). This is associated with anticancer action. Insulin and IGF-1 regulates not only in glucose uptake but also in carcinogenesis through insulin/IGF-1 receptor signalling pathway. IGF-1 production increases with excessive food intake. This binds to the IGF-1 receptors. Through insulin receptor substrate (IRS), the signal is transmitted to phosphoinositide-3-kinase (PI3K) and Akt/ protein kinase B (PKB). Indirect activation of mTORC1 occurs. Insulin receptor through growth factor receptor-bound protein 2 sends signal to Ras/Raf/ERK pathway and promotes cell growth. These pathways are proven to play an important role of cellular metabolism of tumour cells. Therefore, increased levels of insulin and IGF-1 leads to the development of different types of cancer cells. Metformin was proven to reduce insulin levels and inhibit insulin/ IGF signalling pathways. This way it leads to decrease cancer cell development. Metformin inhibits mTORC1 and hence decreases the protein synthesis and cell growth (31). Metformin also leads to anti-tumour growth (32).

It was studied that patients with type 2 diabetes mellitus and metformin had a decreased risk of cancers while compared to those who were on different antidiabetic drugs. In another study, it was observed that in type 2 diabetes mellitus patients on sulfonylureas or insulin, the risk of cancer was more when compared to those patients on metformin treatment. Cancer incidence and mortality decreased with metformin intake in diabetic patients. Metformin use was associated with better outcome in cancer patients (33).

Anti-aging:

Aging is a natural phenomenon which is progressive and universal. Aging leads to a number of actual diseases. If the aging process can be paused, the occurrence of diseases can be reduced (34).

Humans have begun to search for medicines that slow the aging process or have anti-aging properties. Medicines that treat the cause of aging and reduce the related ailments due to aging are under research. These are anti-aging medicines with the goal at extending life span of healthy individuals to have youthful characteristics (34). There are three main factors that are related with aging. They are oxidation, glycation and methylation. There is evidence that metformin acts as an anti-aging agent. It helps slow the rate of aging and retain youth characteristics for a longer period of time than compared to non-metformin users. There are ongoing research about the effect of metformin on anti-aging properties. Researches have proved that metformin is linked with anti-aging factors (34).

There are two mechanisms to describe aging. First one is ROS theory, i.e., reactive oxygen species (35). This occurs when the free radicals increase significantly and damage other cells and organs. The ROS theory explains that by products of oxidative phosphorylation are reactive oxygen species, i.e, free radicals. The ROS leads to DNA damage (36).

The second mechanism is TOR theory. Cellular pathway like IGF-1 axis, MAPK, AKT, PI3K are said to inhibit aging. These are stimulated by mitogens, growth factors, sugars and amino acids. Caloric restriction suppresses the mTOR pathway. The activity of mTOR may be inhibited by rapamycin. Rapamycin has gero-suppressive effects. These include extending the lifespan, prevent age related disorders and reduce cost of patient care. AMPK activation led to an indirect inhibition of mTOR. Metformin acts as an AMPK activator (36,37).

Metformin, Being an AMPK activator, metformin has been proved to have gero-suppressive effects. Extended longevity and lifespan were seen in those taking metformin. Autophagy plays a significant role in gero-suppressive mechanisms. Autophagy protects cell organelles and nutrient supply. Induction of autophagy extends the lifespan. Polyamines cause autophagy. Activation of autophagy induces processes associated with suppression of IGF and mTOR pathways. Therefore metformin acts as an activator of autophagy (38).

Adverse effects of Metformin:

Metformin as all drugs, have unwanted effects as well. Out of the many side effects, lactic acidosis and vitamin B12 deficiency happens to be the major. Other side effects include gastrointestinal disturbances. The most common are anorexia, nausea, abdominal discomfort and diarrhoea. These symptoms may be reduced or alleviated by dose reduction or discontinuation. Although rare, if lactic acidosis occurs, may be fatal (39).

Lactic acidosis

Metformin had been used worldwide for type2 DM and is still in the market today. Phenformin, another biguanide had been used in 1950s. In 1976, reports of lactic acidosis caused imminent hazard and therefore, withdrew phenformin. Withdrawal happened with 306 documented cases of phenformin induced lactic acidosis (40). Therefore, metformin was labelled ‘guilty by association’. Metformin had an incidence rate 10-20 fold less than those who received phenformin (39).

The rate of developing lactic acidosis increases in patients with predisposing factors, such as renal impairment, hepatic disease, congestive heart failure or sepsis. Metformin is renally cleared. In cases of renal failure or decreased creatinine clearance, metformin accumulates. When this happens, it inhibits mitochondrial electron transport. Therefore, it increases anerobic metabolism and lactic production (41).

In case of acetic kidney injury, metformin levels accumulate and lead to nausea and vomiting. The incidence of lactic acidosis is fairly low, but becomes fatal when it occurs. There are three important insights. First, the patients with lactic acidosis has impaired renal function on admission. Secondly, age is the prognostic factor. Thirdly, mortality was lower than other forms of acidosis (42).

Patients with mild to moderate kidney disease should feature dose reduction and monitor kidney function. There are few characteristics to prove metformin induced lactic acidosis. They included lactic acidosis. They include, severe academia (PH <7.1), low serum bicarbonate, markedly elevated lactic acid, history of metformin ingestion and history of renal insufficiency (39).

In a study, the most frequently reported adverse effects were lactic acidosis. The goal in the management of lactic acidosis is to provide airway, breathing and circulatory support and to correct the acidosis with bicarbonates or renal replacement therapy. Early recognition with therapy may improve survival. Toxic drug accumulation of metformin can be reversed by renal replacement therapy (42).

A report from Sweden stated that this continuing metformin in aging patients when they develop cardiovascular diseases could reduce the risk of lactic acidosis. Aggressive resuscitation methods can reverse the severity of acidosis (41). The levels of lactate increase in metformin taking patients. The pyruvate dehydrogenase inhibits conversion of lactate to glucose, thereby causes lactic acidosis (43).

Vitamin B₁₂deficiency:

Metformin and lifestyle modification are used for the treatment of type 2 diabetes mellitus. A common report with long term metformin use is vitamin B₁₂ malabsorption which leads to vitamin B₁₂deficiency (44,45).

A study showed that serum B₁₂ concentrations were decreased by 22%. Initial stages of malabsorption of vitamin B₁₂ deficiency cannot be diagnosed without close attention. 10-30% patients on metformin therapy show vitamin B₁₂ deficiency (46). It was also seen that black race had a lower chance for vitamin B₁₂deficiency (47). In a study, it was proven that being treated with metformin had a 7% greater risk of vitamin B₁₂deficiency than with placebo (48).

The mechanisms leading to vitamin B₁₂ deficiency may be explained by changes in small intestine motility. This cause increased bacterial growth and hence, consumption of vitamin B₁₂. Metformin also inhibits the calcium dependent absorption of vitamin B₁₂(49). Vitamin B₁₂ is an essential nutrient for cognitive and cardiovascular function (50,51). Clinical manifestations of vitamin B₁₂ deficiency include alteration in mental status, megaloblastic anemia and neurological damage (51).

CONCLUSION:

Metformin, the drug initially approved and used for the treatment of Type 2 diabetes mellitus is proven to be effective in many other conditions such as gestational diabetes mellitus, obesity, hypersecretion of ovarian androgens, polycystic ovary syndrome (PCOS), antipsychotic therapy induced weight gain, cancer treatment etc. There are ongoing research about the effect of metformin on anti-aging properties and proved that metformin is linked with anti-aging factors.

REFERENCES:

1 Bailey C, Campbell IW, Chan JCN, Davidson JA, Howlett HCS, Ritz P. Metformin-The Gold Standard: A Scientific Handbook. Chichester: Wiley. 2008; 1-36.

2 Song R. Mechanism of Metformin: A Tale of Two Sites. Diabetes Care. 2016; 39: 187-189.

3 Dronsfield A and Ellis P. Drug Discovery: Metformin and the Control of Diabetes, Education in Chemistry. 2011; 185-187.

4 Metformin History, Drug of a Plant Origin. Available at http://googleweblight.com/i?u=http://www.news-medical.net/health/Metformin-History.aspx&grid=_IBo1qE2&hl=en-IN. Accessed on May 22, 2017.

5 Glucophage- Metformin Hydrochloride, Product Monograph: Licensed to Bristol-Myers Squibb Company. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/020357s037s039,021202s021s023lbl.pdf. April 2017. Reference ID: 4079189. Accessed on May 22, 2017.

6 Non-Diabetic Uses of Metformin. Available at http://oureverydaylife.com/nondiabetic-uses-metformin-11813.htm. Accessed on May 23, 2017.

7 NICE Guidelines, Type 2 diabetes in adults: Management, 2 Dec. 2015, available at http://nice.org.uk/guidance/ng28. Accessed on May 23, 2017.

8 Mahler RJ and Adler ML. Clinical Review 102, Type 2 DM: Update on Diagnosis, Pathophysiology, and Treatment. The Journal of Clinical Endocrinology & Metabolism. 1999; 84(4): 1165-1171.

9 Houghton L. Nottingham University Hospitals NHS, NHS Trust. Metformin in Pregnancy. Diabetes Antenatal Clinic. 2011; Review 2016. Available at www.nuh.nhs.uk. Accessed on August 10, 2017.

10 Glucophage-Metformin Hydrochloride. Product Monograph: Manufacturer’s Standard, 500 mg and 850 mg tablets, oral hypoglycaemic agent. Registered trademark of Merck Sante. Used under license Sanofi Aventis version 4.2, Oct 22, 2014.

11 Seshiah V, Sahay BK, Das AK, Balai V, Siddharth Shah, Samar Banerjee, Muruganathan A, Rao PV, et al. Diagnosis and Management of GDM: Indian Guidelines. Medicine Update. 2013; 23: 201-204.

12 Lathief S and Pal L. Advances in Treatment options for Polycystic Ovarian Syndrome. Female Endocrinology. US Endocrinology. 2012; 8 (1): 57-64.

13 Hsin-Shih W. The Role of Metformin in the Treatment of Polycystic Ovarian Syndrome (PCOS). Forum. Chang Gung Med J. 2006; 29 (5): 445-447.

14 Spritzer PM. PCOS: Reviewing Diagnosis and Management of Metabolic Disturbances. Arq Bras Endocrinal Metab. 2014; 58 (2): 182-187.

15 Yilmaz M, Biri A, Karakoc A, et al. The Effects of Rosiglitazone and Metformin on Insulin Resistance and Serum Androgen Levels in Obese and Lean Patients with Polycystic Ovary Syndrome. J Endocrinol Invest. 2005; 28: 1003-1008.

16 Mathur R, Alexander CJ, Yano J, Trivax B, Azziz R. Use of Metformin in PCOS. American Journal of Obstetrics and Gynecology. 2008; 199 (6): 596-609.

17 Puska P, Nishida C, Porter D. World Health Organization. Global Strategy on Diet, Physical Activity and Health, Obesity and Overweight, WHO. 2003.

18 Levri KM, Slaymaker E, Last A, Yeh J, Ference J, Frank D’Amico, Wilson SA. Metformin as Treatment for Overweight and Obese Adults: A Systemic Review. Annals of Family Medicine. 2005; 3 (5): 457-461.

19 Aa MP, Hoving V, Garde EMW, Boer A, Knibbe CAT, Vorst MMJ. The Effect of Eighteen- Month Metformin Treatment in Obese Adolscents: Comparison of Results Obtained in Daily Practice with Results from a Clinical Trial. Journal of Obesity. 2016; 2016(2016): 1-7.

20 Astrup A. Treatment of Obesity. International Textbook of Diabetes Mellitus. Third Edition: 2004; 673-690.

21 Seifarth C, Schehler B, Schneider HJ. Effectiveness of Metformin on Weight Loss in Non-Diabetic Individuals with Obesity. Exp Clin Endocrinol Diabetes. 2013; 121: 27-31.

22 Fenton WS and Chavez MR. Medication Induced Weight Gain and Dyslipidemia in Patients with Schizophrenia. Am J Psychiatry. 2016; 163(10): 1697-1704.

23 Generali JA and Cada DJ. Off- Label Drug Uses, Metformin: Prevention and Treatment of Antipsychotic-Induced Weight Gain. Hosp Pharm. 2013; 48(9): 734-735.

24 Schumann SA and Ewigman B. Can Metformin Undo Weight Gain Induced by Antipsychotics? The Journal of Family Practice. 2008; 57 (8): 526-530.

25 De Silva VA, Suraweera C, Ratnatunga SS, Dayabandara M, Wanniarachchi N, Hanwella R. Metformin in Prevention and Treatment of Antipsychotic Induced Weight Gain: A Systemic Review and Meta-Analysis. BMC Psychiatry. 2016; 16 (341): 1-10.

26 Praharaj SK, Jana AK, Goyal N, Sinha VK. Metformin for Olanzapine-Induced Weight Gain: A Systematic Review and Meta- analysis. British Journal of Clinical Pharmacology. 2011; 71(3): 377-382.

27 Kasznicki J, Sliwinska A, Drzewoski J. Metformin in Cancer Prevention and Therapy. Annals of Translational Medicine. 2014; 2(6): 1-11.

28 Zakikhani M, Dowling R, Fantus IG, Sonenberg N, Dollak M. Metformin is an AMP-Kinase-Dependent Growth Inhibitor for Breast Cancer Cells. Cancer Res. 2006; 66(21): 10269-10273.

29 Dowling RJO, Zakikhani M, Fantus IG, Pollak M, Sonenberg N. Metformin Inhibits Mammalian Target of Rapamycin - Dependent Translation Initiation in Breast Cancer Cells. American Association for Cancer Research Journals. 2007; 67(22): 10804-10812.

30 Hawley SA, Gadalla AE, Olsen GS, Hardie DG. The Antidiabetic Drug Metformin Activates the AMP-Activated Protein Kinase Cascade via an Adenine Nucleotide- Independent Mechanism. Diabetes. 2002; 51: 2420-2425.

31 Menendez JA, Silvia Cufi, Oliveras-Ferraros C, Luciano Vellon, Jorge Joven, Vazquez-Martin A. Gerosuppressant Metformin: less is more. Aging. 2011; 3(4): 348-362.

32 Rocha GZ, Dias MM, Ropelle ER, Osorio-Costa F, Rossato FA, Vercesi AE, Saad MJA, Carvalheira JBC. Metformin Amplifies Chemotherapy-Induced AMPK Activation and Antitumoral Growth. American Association for Cancer Research. 2011; 17 (12): 3993-4005.

33 Sahra IB, Marchand- Brustel YL, Tanti JF, Bost F. Metformin in Cancer Therapy: A New Perspective for an Old Antidiabetic Drug. American Association for Cancer Research. Molecular Cancer Therapeutics. 2010; 9(5): 1092-1099.

34 Arora BP. Anti-aging Medicine. Indian J. Plastic Surgery Supplement. 2008; 41: S130-S133.

35 Foretz M, Guigas B, Bertrand L, Pollak M, Viollet B. Metformin: From Mechanism of Action to Therapies. Cell Metabolism 20. 2014; 20(6): 953-966.

36 Podhorecka M, Ileanz B, Dmoszynska A. Metformin- it’s Potential Anti-Cancer and Anti-Aging Effects. Postepy Hig, Medycyny Doswiadczalnej. 2017; 71: 170-175.

37 Hawley SA, Gadalla AE, Olsen GS, Hardie DG. The Antidiabetic Drug Metformin Activates the AMP-Activated Protein Kinase Cascade via an Adenine Nucleotide- Independent Mechanism. Diabetes. 2002; 51: 2420-2425.

38 Menendez JA, Cufi S, Oliveras-Ferraros C, Vellon L, Joven J, Vazquez-Martin A. Gerosuppressant Metformin: less is more. Aging. 2011; 3(4): 348- 362.

39 Suh S. Metformin- Associated Lactic Acidosis. Endocrinology Metabolism. 2015; 30: 45-46.

40 DeFronzo R, Fleming GA, Kim Chen, Bicsak TA. Metformin-Associated Lactic Acidosis: Current Perpectives on Causes and Risks. Metabolism Clinical and Experimental. 2016; 65: 20-29.

41 Misbin RI. The Phantom of Lactic Acidosis due to Metformin in Patients with Diabetes. Diabetes Care. 2004; 27(7): 1791-1793.

42 Zhang J, Sunderkrishnan R, Brackett S, Qureshi M, Shensky K, Gulati R. Metformin Associated Lactic Acidosis. The Medicine Forum. 2015; 16(9): 1-2.

43 Renda F, Mura P, Finco G, Ferrazin F, Pani L, Landoni G. Metformin- Associated Lactic Acidosis Requiring Hospitalization. A National 10 year Survey and a Systematic Literature Review. European Review for Medical and Pharmacological Sciences. 2013; 17(Supplement 1): 45-49.

44 Kumthekar AA, Gidwani HV, Kumthekar AB. Metformin Associated B₁₂deficiency. JAPI. 2012; 60: 58-59.

45 Kang D, Yun JS, Ko SH, Lim TS, Ahn YB, Park YM, Ko HS. Higher Prevalence of Metformin-Induced Vitamin B₁₂ Deficiency in Sulfonylurea Compared with Insulin Combination in Patients with Type 2 Diabetes: A Cross- Sectional Study. PLoS ONE. 2014; 9(10):1-9.

46 Reinstatler L, Qi YP, Williamson RS, Garm JV, Oakley GP. Association of Biochemical B₁₂deficiency with Metformin Therapy and Vitamin B₁₂Supplements. Diabetes Care. 2012; 35: 327-333.

47 Ahmed MA, Muntingh G, Rheeder P. Vitamin B₁₂Deficiency in Metformin-Treated Type-2 Diabetes Patients, Prevalence and Association with Peripheral Neuropathy. BMC Pharmacology and Toxicology. 2016; 17(44):1-10.

48 Jager J, Kooy A, Lehert P, Wulffele MG, Kolk J, Bets D, Verburg J, Donker AJM, Stehouwer CDA. Long Term Treatment with Metformin in Patients with Type 2 Diabetes and Risk of Vitamin B12 Deficiency: Randomised Placebo Controlled Trial. BMJ. 2010; 2010 (340): 1-7.

49 Jeetendra S and Tushar B. Metformin Use and Vitamin B₁₂Deficiency in Patients with Type 2 Diabetes Mellitus. MVP Journal of Medical Sciences. 2016; 3(1): 67-70.

50 Kibirige D and Mwebaze R. Vitamin B12 Deficiency Among Patients with Diabetes Mellitus: Is Routine Supplementation Justified? Diabetes and Metabolic Disorders. 2013; 12(17): 1-6.

51 Fatima S and Noor S. A Review on Effects of Metformin on Vitamin B12 Status. American Journal of Phytomedicine and Clinical Therapeutics. 2013; 1(8): 652-660.

Received on 14.02.2018 Modified on 29.03.2018

Research J. Pharm. and Tech 2018; 11(6): 2701-2708.

DOI: 10.5958/0974-360X.2018.00499.7