Which Extended-Release Metformin products are best: Glucophage XR, Glumetza or Fortamet?
Metformin is a popular medication for diabetes. In fact, the American Diabetes Association (ADA) recommends it as a first-choice treatment for people with type 2 diabetes.
You have options when it comes to metformin, though.
First, metformin is available in 2 forms: immediate-release(IR) and extended-release(ER). Second, the ER form is available under 3 brand names, each with their own generic versions due to the differences in the way they are released.
All these products release the active ingredient (metformin) slowly over time, but via different mechanisms and have slightly different pharmacokinetic profiles (e.g. rate and extent of absorption).
Is Glucophage XR, Glumetza, or Fortamet more effective for diabetes?
Extended-release metformin products are thought to have an advantage over immediate-release ones in terms of their side effect profile since the active ingredient (metformin) is released over time instead of all at once.
Not only do they have a lower incidence of nausea, diarrhea, stomach cramping and vomiting than immediate-release tablets, but studies also show that they are taken more consistently by patients (i.e. better adherence), which presumably would lead to better blood sugar control.
How do Glucophage XR, Glumetza, and Fortamet work?
Glucophage XR tablets utilize a ‘dual hydrophilic polymer system’.
These tablets swell when they come into contact with gastric juices and form a gel layer. Metformin is then slowly released via diffusion through this newly-formed gel matrix.
Peak drug concentrations in clinical trials are reached about 7 hours after dosing. It should be taken with food to increase overall absorption.
Fortamet tablets utilize ‘single-composition osmotic technology (SCOT)’. Osmotic technology tablets utilize osmotic pressure to release a drug at a consistent rate over time.
The tablet has a small opening on one end where water enters, causing the drug layer in the tablet to dissolve. The entering water also increases the osmotic pressure, and the drug is pumped out the tablet opening at a constant rate.
Peak drug concentrations are reached approximately 6 hours after dosing and like Glucophage XR, it should be taken with food.
Glumetza tablets use gastric-retentive technology, which protects them from dissolving in the stomach. These tablets release metformin after being emptied from the stomach, in the upper gastrointestinal tract.
Peak concentrations are reached around 7 hours after dosing and are recommended to be taken after a meal for best absorption.
Brand-name metformin ER medications (and their corresponding generics) are available in the following strengths:
Dosing for metformin will depend on how you respond to it. Because metformin can cause significant stomach problems (e.g., diarrhea, nausea, gas)
Choosing an Extended-Release Metformin
In terms of which extended-release metformin products is best, again, there are no comparative studies.
The choice will likely depend on the following:
The dose are you taking (e.g. Glucophage XR is the only extended-release product available in a 750 mg dose. Fortamet and Glumetza are only available in doses of 500 mg and 1000 mg)
Which is covered by your insurance (per your formulary)
Whether or not you need a generic product
We could certainly go through the clinical trials for each drug to see how they affected certain values like blood glucose and HbA1C, however, picking information from trials that aren’t under identical conditions does not lead to an accurate comparison.
For example, patient characteristics (e.g. gender, length of time with diabetes) doses used, how doses were adjusted, concurrent medications and length of therapy are all different in clinical trials for each extended-release drug.
In trials, all three drugs did show statistically significant decreases in fasting blood glucose, HbA1c, and body weight but, as discussed above, we can’t make a definitive determination on which is ‘better.’
These 3 drugs are not interchangeable at the pharmacy. If your doctor writes you a prescription for Glumetza, for example, you can’t ask your pharmacist for Glucophage XR instead.
If you want a specific brand, you will need to ask your doctor for that specific prescription. However, if you are prescribed one of these brands, you can ask your pharmacist to give you its generic version instead.