PTCB Guide to Metformin.

Metformin’s Importance in the Top 200 List.

Metformin is one of the most prescribed drugs in the United States. An estimated 85 million prescriptions are written for metformin each year, primarily for its use in managing type 2 diabetes.

As a key top 200 medicine, pharmacy technicians are expected to have a thorough understanding of this essential drug. For the PTCB exam, technicians are required to learn:

• Indications of metformin – what it’s used to treat
• How the drug works, its mechanism of action
• Major side effects and adverse effects
• Key drug interactions
• Brand names

As with every drug for the PTCB exam, technicians are not required to know mechanisms, side effects, and interactions in detail. Instead, just the basics need to be covered – the kind of detail we cover in this study guide.

Remember, most metformin products dispensed today are generic metformin (immediate-release or extended-release), but there are still a few branded formulations on the market:

• Glumetza — a branded extended-release metformin formulation still marketed in the U.S. and available as both brand and generic versions.

• Riomet — a metformin oral solution brand (and its ER suspension forms) that is still recognized.

• Various fixed-dose combination products that include metformin (e.g. Xigduo XR with dapagliflozin, Glucovance with glyburide, Janumet with sitagliptin, Trijardy XR with empagliflozin/linagliptin) remain active in the US market.

Earlier brand names like Glucophage, Glucophage XR, and Fortamet have been discontinued in their original forms in the US, though generic versions of these extended-release formulations are widely available.

What is metformin used to treat – and how does it work?

Metformin is primarily used to treat type 2 diabetes, where it helps lower blood glucose levels and is often considered first-line therapy.

It is also used off-label in polycystic ovary syndrome (PCOS) to improve insulin resistance and help regulate menstrual cycles. For the PTCB exam, technicians should recognize metformin as a biguanide antidiabetic agent commonly prescribed for long-term glucose control.

Metformin works through three main means:

• It decreases hepatic glucose production (gluconeogenesis) – in other words, it reduces sugar production by the liver (hepatic).
• It reduces glucose absorption from the intestines.
• It improves peripheral insulin sensitivity. Peripheral insulin sensitivity refers to how well the body’s tissues – mainly muscle and fat cells – respond to insulin.

Note that metformin does not stimulate insulin release, which is why it has a low risk of hypoglycemia when used alone (for more on insulins on the PTCB exam, check out our complete insulin study guide).

Side Effects.

Side effects most associated with metformin include:

• Gastrointestinal side effects – especially nausea, diarrhea, abdominal discomfort
• Metallic taste

These side effects are more likely when treatment is started or when doses are increased. Taking metformin with food or using extended-release formulations can help reduce these effects.

A rare but serious adverse effect of metformin is lactic acidosis, which is more likely in patients with significant kidney impairment, severe dehydration, or hypoxia. Pharmacy technicians should be aware that long-term metformin use is also associated with vitamin B12 deficiency, and that, as we learned, metformin does not usually cause hypoglycemia when used alone.

Unlike many other oral antidiabetic drugs, metformin can cause weight loss rather than weight gain.

Drug Interactions.

For the pharmacy technician exam, you should know only major drug interactions with metformin.

For instance, drugs that elevate blood glucose oppose the blood sugar lowering effects of metformin. These drugs include:

• Prednisolone – a corticosteroid
• Thiazide diuretics – such as hydrochlorothiazide
• Loop diuretics – such as furosemide

Drugs that can cause kidney damage can increase the risk of adverse effects with metformin. This includes NSAIDs, diuretics (again), and ACE inhibitors.

Finally, metformin must be withheld for 48-hours before/after the use of IV contrast media (IV contrast media is used for CT scans etc.). In this situation, there is an increased risk of kidney damage and therefore adverse effects with metformin.

Sample PTCB Questions – Metformin.

Below we put together five questions on this widely prescribed medicine, all of which reflect the kind of questions that get asked on the PTCB exam. Attempt each question first before learning more about the correct answers in the section directly below.

Question 1.

Metformin is primarily used in the management of which condition?

a. Type 1 diabetes mellitus

b. Type 2 diabetes mellitus

c. gestational diabetes only

d. diabetic ketoacidosis

Question 2.

Which of the following is a common side effect of metformin?

a. hypoglycemia

b. weight gain

c. gastrointestinal upset

d. hair loss

Question 3.

A serious but rare adverse effect associated with metformin is:

a. pancreatitis

b. lactic acidosis

c. QT prolongation

d. agranulocytosis

Question 4.

What is the primary mechanism by which metformin lowers blood glucose levels?

a. stimulating insulin release from the pancreas

b. increasing glucose absorption in the intestine

c. decreasing hepatic glucose production

d. blocking glucose reabsorption in the kidney

Question 5.

Which of these drugs opposes the blood sugar lowering effects of metformin?

a. phenytoin

b. diazepam

c. lovastatin

d. prednisolone

Answer Explanations.

Answer to Question 1 – b. Type 2 diabetes mellitus

Metformin is widely used in the management of type 2 diabetes, either alone or in combination with other drugs. It is also used in the treatment of PCOS, polycystic ovary syndrome.

Answer to Question 2 – c. Gastrointestinal upset

Metformin commonly causes GI upset, such as nausea, diarrhea, and abdominal discomfort. It can also cause a metallic taste.

Answer to Question 3 – b. Lactic acidosis

In rare cases, metformin can cause lactic acidosis. This is typically due to factors such as kidney disease, chronic alcohol consumption, and high doses of metformin for prolonged periods.

Answer to Question 4 – c. Decreasing hepatic glucose production

Metformin works in part by decreasing production of sugars by the liver, or ‘hepatic glucose production’. This lowers blood sugar levels in patients with diabetes.

Answer to Question 5 – d. Prednisolone

Corticosteroids such as prednisolone increase blood sugar levels, as well as increasing the risk of developing diabetes. They therefore directly oppose the blood sugar lowering effects of metformin. Diuretics also oppose the blood sugar lowering effects of metformin.

PTCB Metformin Cheat Sheet.

Over the course of today’s PTCB guide to metformin, we learned:

Drug class

• Biguanide
• First-line medicine in the management of type 2 diabetes

Indications

• Type 2 diabetes (primary use)
• May be used off-label for PCOS (polycystic ovary syndrome)

Mechanism of action

• Decreases hepatic glucose production (gluconeogenesis)
• Improves peripheral insulin sensitivity
• Decreases intestinal glucose absorption
• Does not stimulate insulin release

Because it does not increase insulin secretion, it has a low risk of hypoglycemia when used alone.

Formulations

• Immediate-release (IR)
• Extended-release (ER/XR)
• Oral tablets and oral solution

Dosing and administration

• Usually taken with meals to reduce the risk of GI upset
• ER tablets should not be crushed or chewed
• Dose adjustments may be required in kidney disease

Common side effects

• Nausea
• Diarrhea
• Abdominal discomfort
• Metallic taste

(Note: GI effects are very common when starting therapy.)

Serious adverse effect

• Lactic acidosis (rare but life-threatening)
  • Risk increases in severe renal impairment, dehydration, or hypoxia

Monitoring

• Long-term use may cause vitamin B12 deficiency

Important considerations

• Typically does not cause hypoglycemia alone
• May cause modest weight loss
• Temporarily discontinued before IV contrast media procedures
• Drugs that oppose the blood sugar lowering effects of metformin include corticosteroids (such as prednisolone) and diuretics.

Brand names:

• Most commonly dispensed as generic metformin
• Some branded names include Glumetza and Riomet
• Discontinued brand names include Glucophage and Fortamet

Hope you found today’s metformin PTCB guide helpful! Check back to our blog soon for more exclusive content to help you study and prepare for your pharmacy technician exam.

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