Metformin vs. Janumet

  • Medical Editor: John P. Cunha, DO, FACOEP
    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

What's the difference between metformin vs. Janumet?

What is metformin? What is Janumet?

Metformin is an oral medication that lowers blood glucose (sugar) by influencing the body's sensitivity to insulin and is used for treating type 2 diabetes. Metformin acts by increasing the sensitivity of liver, muscle, fat, and other tissues to the uptake and effects of insulin, which lowers the level of sugar in the blood. Metformin does not increase the concentration of insulin in the blood and does not cause excessively low blood glucose levels (hypoglycemia) when used alone. Metformin can reduce complications of diabetes such as heart disease, blindness, and kidney disease. Metformin is also used to treat polycystic ovaries and weight gain due to medications used for treating psychoses.

Janumet (metformin and sitagliptin) is used to reduce blood glucose (sugar) levels in individuals with type 2 diabetes. Type 2 diabetes results when there is reduced sensitivity of muscle and fat to the effects of insulin. Metformin lowers blood glucose by increasing the sensitivity of liver, muscle, fat, and other tissues to the effects of insulin. Increasing the sensitivity of tissues to insulin causes more glucose to be removed from blood and thereby reduces the level of glucose in the blood. Sitagliptin is a DPP-4 inhibitor that reduces blood sugar levels in patients with type 2 diabetes. Sitagliptin works to reduce blood glucose levels by inhibiting the DPP-4 enzyme and increasing the levels of the hormones GLP-1 and GIP.

What are the side effects of metformin and Janumet?

Metformin

The most common side effects with metformin are

These symptoms occur in one out of every three patients. These side effects may be severe enough to cause therapy to be discontinued in one out of every 20 patients. These side effects are related to the dose of the medication and may decrease if the dose is reduced.

Metformin may also cause:

A serious but rare side effect of metformin is lactic acidosis. Lactic acidosis occurs in one out of every 30,000 patients and is fatal in 50% of cases. The symptoms of lactic acidosis are

  • weakness,
  • trouble breathing,
  • abnormal heartbeats,
  • unusual muscle pain,
  • stomach discomfort,
  • light-headedness, and
  • feeling cold.

Patients at risk for lactic acidosis include those with reduced function of the

Janumet

The most common side effects of Janumet are:

Lactic acidosis is a serious side effect of metformin that occurs in one out of every 30,000 patients and is fatal in 50% of cases. The symptoms of lactic acidosis are weakness, trouble breathing, abnormal heartbeats, unusual muscle pain, stomach discomfort, light-headedness and feeling cold. Patients at risk for lactic acidosis include those with reduced function of the kidneys or liver, congestive heart failure, severe acute illnesses, and dehydration. Janumet should be discontinued immediately if lactic acidosis is suspected.

What is the dosage of metformin and Janumet?

Metformin

  • For treating type 2 diabetes in adults, metformin (immediate release) usually is begun at a dose of 500 mg twice a day or 850 mg once daily. The dose is gradually increased by 500 mg weekly or 850 mg every two weeks as tolerated and based on the response of the levels of glucose in the blood. The maximum daily dose is 2550 mg given in three divided doses.
  • If extended tablets are used, the starting dose is 500 mg or 1000 mg daily with the evening meal. The dose can be increased by 500 mg weekly up to a maximum dose of 2000 mg except for Fortamet (2500 mg of Fortamet, once daily or in two divided doses). Glumetza tablets (500 -1000mg formulations are given once daily (either 1000 to 2000mg). Fortamet and Glumetza are modified release formulations of metformin. Metformin should be taken with meals.
  • For pediatric patients 10-16 years of age, the starting dose is 500 mg twice a day. The dose can be increased by 500 mg weekly up to a maximum dose of 2000 mg in divided doses.
  • Children older than 17 years of age may receive 500 mg of extended release tablets daily up to a maximum dose of 2000 mg daily. Extended release tablets are not approved for children younger than 17 years of age.
  • Metformin-containing drugs may be safely used in patients with mild to moderate renal impairment. Renal function should be assessed before starting treatment and at least yearly.
  • Metformin should not be used by patients with an estimated glomerular filtration rate (eGFR) below 30 mL/minute/1.73 m2 and starting metformin in patients with an eGFR between 30-45 mL/minute/1.73 m2 is not recommended.
  • Metformin should be stopped at the time of or before administering iodinated contrast in patients with an eGFR between 30 and 60 mL/minute/1.73 m2; in patients with a history of liver disease, alcoholism, or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Kidney function should be evaluated 48 hours after receiving contrast and metformin may be restarted if kidney function is stable.

Janumet

  • Janumet is taken twice daily with meals, and the starting dose is based on the patient's current dose of sitagliptin and metformin. The maximum dose of Janumet is 100/2000 mg daily.

What drugs interact with metformin and Janumet?

Metformin

  • Cimetidine (Tagamet), by decreasing the elimination of metformin from the body, can increase the amount of metformin in the blood by 40%. This may increase the frequency of side effects from metformin.
  • Ioversol (Optiray) and other iodinated contrast media may reduce kidney function, which reduces elimination of metformin, leading to increased concentrations of metformin in the blood. Metformin should be stopped 48 hours before and after use of contrast media.
  • Thiazide diuretics, steroids, estrogens, and oral contraceptives may increase blood glucose and reduce the effect of metformin. When these drugs are stopped, patients should be closely observed for signs of low blood glucose.
  • Alcohol consumption increases the effect of metformin on lactate production, increasing the risk of lactic acidosis.

Janumet

  • Cimetidine (Tagamet), by decreasing the elimination of metformin from the body, can increase the level of metformin in the blood by 40%. This may increase the frequency of side effects from metformin and Janumet.

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Are metformin and Janumet safe to use while pregnant or breastfeeding?

Metformin

  • There are no adequate studies in pregnant women. Most experts agree that insulin is the best treatment for pregnant women with diabetes.
  • Metformin is excreted into breast milk and can, therefore, be transferred to the nursing infant. Nursing mothers should not use metformin.

Janumet

  • There are no adequate studies of Janumet or the individual components in pregnant women. Most experts agree that insulin is the appropriate treatment for diabetes during pregnancy.
  • It is unknown whether sitagliptin is secreted in human breast milk. However, metformin is excreted into breast milk and can, therefore, be transferred to the nursing infant.

Summary

Metformin and Janumet (metformin and sitagliptin) are used to treat type 2 diabetes. Metformin is also used to treat polycystic ovaries and weight gain due to medications used for treating psychoses.

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Medically Reviewed on 12/21/2018
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