Metformin

Metformin is an oral antidiabetic medication from the biguanide class and is considered the first-line treatment for type 2 diabetes mellitus. It lowers blood sugar levels without causing low blood sugar (hypoglycemia).

Metformin is available under various brand names, including Glucophage®, Siofor®, and Metformin Lich®. Numerous generics are available.

The active ingredient is usually used as long-term therapy and is often combined with other antidiabetic medications or insulin when blood sugar control with metformin alone is not sufficient.

Metformin acts on glucose metabolism through several mechanisms:

Inhibition of glucose production in the liver:

• Reduces hepatic gluconeogenesis (the formation of new glucose)
• This is the most important mechanism of action

Improvement of insulin sensitivity:

• Increases glucose uptake into muscle and fat cells
• The body's cells respond better again to the body's own insulin

Delayed glucose absorption in the intestine:

• Slows the absorption of sugar from food

Advantages:

• No increased risk of hypoglycemia when used alone
• Weight-neutral to slightly weight-reducing
• Proven cardiovascular benefit

Metformin is suitable for:

• Adults with type 2 diabetes mellitus
• As the first drug therapy after lifestyle changes
• In combination with other antidiabetic medications or insulin
• Overweight patients with type 2 diabetes (particular benefit)

Not suitable:

• Type 1 diabetes
• Severe impairment of kidney function (eGFR < 30 ml/min)
• Acute conditions with a risk of lactic acidosis
• Breastfeeding

Available strengths:

• 500 mg film-coated tablets
• 850 mg film-coated tablets
• 1000 mg film-coated tablets

Extended-release tablets:

• 500 mg, 750 mg, 1000 mg (extended release)

Usual dosage:

• Starting dose: 500 mg 1-2x daily or 850 mg 1x daily
• Increase every 1-2 weeks
• Maximum dose: 3000 mg/day (usual: 2000 mg/day)

How to take:

• Take with or after meals (reduces gastrointestinal complaints)
• Swallow the tablets whole with water, without chewing
• Do not split or chew extended-release tablets

Dosing schedule (typical):

• Weeks 1-2: 500 mg in the evening
• Weeks 3-4: 500 mg in the morning and in the evening
• Then, if needed, increase to 3x 500 mg or 2x 1000 mg

Important notes:

• Take regularly, even if you have no symptoms
• Stop before or at the latest at the time of examinations with iodinated contrast agents and resume no earlier than 48 h afterward, once your kidney function has been rechecked and is stable
• In case of surgery, pause as instructed by your doctor
• Attend regular kidney function checks

Metformin must not be taken in cases of:

• Severe renal insufficiency (eGFR < 30 ml/min)
• Diabetic ketoacidosis or diabetic precoma
• Acute conditions with a risk of kidney damage (dehydration, severe infections, shock)
• Hepatic insufficiency
• Alcohol intoxication, alcoholism
• Decompensated heart failure (acute and unstable)
• Conditions with tissue hypoxia (cardiovascular shock, respiratory insufficiency)

Use with caution in cases of:

• Impaired kidney function (eGFR 30-45 ml/min: max. 1000 mg/day)
• Elderly patients (more frequent kidney function checks)
• Iodinated contrast agents (stop before or at the latest at the time of the examination, resume no earlier than 48 h afterward, once your kidney function has been rechecked and is stable)

Pregnancy/breastfeeding: If clinically necessary, metformin may be considered during pregnancy and in the period around conception, in addition to or as an alternative to insulin. Breastfeeding while taking metformin is not recommended.

Very common (>10%):

• Nausea
• Vomiting
• Diarrhea
• Abdominal pain
• Loss of appetite

Note: These complaints occur mainly at the start of treatment and usually improve after a few weeks. Taking the medication with food and increasing the dose slowly help.

Common (1-10%):

• Taste disturbances (metallic)
• Vitamin B12 deficiency with long-term use

Very rare:

• Lactic acidosis (potentially life-threatening)
• Liver function disorders
• Skin reactions

Long-term: If you take it for years, have your vitamin B12 levels checked regularly.

Alcohol: Increased risk of lactic acidosis. Avoid excessive alcohol consumption.

Contrast agents (iodinated): Stop metformin before or at the latest at the time of the examination and resume no earlier than 48 hours afterward, once your kidney function has been rechecked and is stable. Risk of kidney damage.

Caution when taking at the same time as:

• ACE inhibitors, diuretics – kidney function may worsen
• Corticosteroids – may raise blood sugar
• Other antidiabetic medications or insulin – the risk of hypoglycemia increases in combination

Interactions via the kidneys: Medications that affect kidney function require special monitoring.