What is the difference between Fortamet XR and Glumetza - Aren't they both metformin extended release?
You are right that both of the products that you mentioned are metformin. They differ in their release mechanism. All of the products are similar in the fact that they are extended release. The whole point of these extended release products is to reduce the gastrointestinal side effects that many patients experience when taking metformin. There are 3 different types of metformin extended release formulations:
This metformin product uses what is called a "dual hydrophilic polymer system" as its release mechanism. The outer layer of the tablets contain no drug at all. It's purpose is to completely surround inner polymer particles containing metformin. After the tablet is taken by mouth, the tablet absorbs moisture. In fact, hydrophilic means "water loving". The absorbed moisture causes the tablet to swell forming a gel layer on the outside of the tablet. It is this newly formed gel layer that releases metformin into the body at a controlled rate. It is intended to be dosed once daily. The peak concentrations of metformin in the body using the dual hydrophilic release polymer mechanism usually ranges anywhere from 4-8 hours. It is recommended to take this product with food as it increases the amount of drug that is absorbed in the body.
This metformin product uses single-composition osmotic technology. This technology is somewhat similar to what is used in the Glucophage XR tablets. Metformin is contained inside a semi-permeable membrane inside the tablet. The tablet contains two laser drilled holes on either side. When water is absorbed in the tablet, the osmotic pressure forces drug out of the laser drilled holes at a controlled rate. Fortamet is also intended to be dosed once daily and like Glucophage XR, it should be taken with food. It's important to note that with this product, you typically can see the shell of the tablet in your stool.
This metformin product used gastric-retentive technology to release metformin into the body. With this release mechanism, the drug actually stays inside the stomach for an extended period of time, slowly releasing the drug into the upper GI tract. After the tablet is taken by mouth, it absorbs moisture and swell to 150% its original size. This enlarged size allows the drug to stay in the stomach while metformin is being released over an 8 hour time period. After this period, the tablet is almost completely broken and will continue through the Gi tract. Again, it is recommended to take the drug with food.