MetforminNursing considerations

Side effects by what to assess

Sources: [1][2][3][4]

Blood glucose

Why

Glycemic control and hypoglycemia with insulin or secretagogues

When

Guides titration

Normal

Fasting 70 to 99 mg/dL.

Sources: [1][2][3]

eGFR (glomerular filtration rate)

Why

Lactic acidosis risk from renal accumulation

When

Before starting, at least yearly, more often in older adults, and 48 hours after iodinated contrast

Act on

Below 30: stop. 30 to 45: do not start; reassess continuing below 45

Normal

90 to 120 mL/min/1.73 m². Below 60 for 3 or more months points to chronic kidney disease.

Sources: [1][2][3][4]

Hemoglobin A1c

Why

Long-term glycemic control

When

Periodically per diabetes care standards

Normal

Below 5.7% is normal and 6.5% or higher indicates diabetes. Many people with diabetes aim for below 7%.

Sources: [1]

Vitamin B12

Why

B12 deficiency and anemia

When

B12 every 2 to 3 years; blood counts yearly

Act on

Manage abnormalities; supplement or stop

Normal

299 to 1054 pg/mL.

Sources: [1][2]

High-alert status

Metformin is not on the ISMP acute care high-alert list. Insulin and oral sulfonylureas are.

Sources: [1]

Narrow therapeutic index

The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.

Sources: [1]

Boxed warning

Lactic acidosis. Rare but can be fatal, with a subtle onset of malaise, myalgias, breathing trouble, sleepiness, and abdominal pain. Risk rises with renal impairment, age 65 or older, iodinated contrast, surgery, hypoxic states, heavy alcohol use, hepatic impairment, and drugs such as topiramate. If suspected, stop metformin, give supportive care in hospital, and start hemodialysis promptly.

Sources: [1]

Antidote or reversal

No antidote. Metformin is dialyzable, with clearance up to 170 mL/min, so hemodialysis is used for lactic acidosis and can help in overdose.

Sources: [1][2]

Patient teaching

• Stop metformin and call the prescriber for unexplained fast breathing, muscle aches, unusual sleepiness, or feeling very unwell
• Avoid heavy alcohol use
• Get kidney function checked regularly
• Tell every provider about metformin before surgery or an imaging test with contrast
• Low blood sugar can happen when it is combined with insulin or a sulfonylurea; know the symptoms and treatment
• Regular blood counts and B12 checks are needed
• It can restore ovulation in some women who were not ovulating, so unplanned pregnancy is possible

Sources: [1]

Sound-alike and look-alike names

• metFORMIN and metroNIDAZOLE

Sources: [1]

Adult dose

Type 2 diabetes

Start 500 mg twice daily or 850 mg once daily with meals. Increase by 500 mg weekly or 850 mg every 2 weeks, to a maximum of 2,550 mg per day in divided doses.

Sources: [1]

Renal adjustment

Check eGFR before starting and at least yearly. Below 30: contraindicated. 30 to 45: do not start. If eGFR falls below 45 on therapy, weigh benefit against risk; stop if it falls below 30.

Sources: [1][2]

Hepatic adjustment

Not recommended with clinical or lab evidence of hepatic disease, because impaired lactate clearance raises lactic acidosis risk.

Sources: [1][2]

Mechanism

A biguanide. It cuts glucose output from the liver, reduces glucose absorption from the gut, and improves insulin sensitivity so muscle takes up more glucose. Insulin secretion does not increase.

Sources: [1]