Metformin vs Metformin ER

I'm seeing quite a few posts on BBSes from people who are having problems with metformin because of side effects that could be eliminated if they were taking the extended release form of this drug.

For some reason, many family doctors don't seem to be aware that there is a ER version of this drug that has such benefits. This is probably because metformin is a cheap generic and isn't promoted by herds of beautiful ex-cheerleaders turned drug company salespushers who "educate" doctors about far more expensive--and less effective--newer drugs.

Here are the facts: Metformin (also sold under the brand name Glucophage) comes in a regular version which is taken at meal time, three times a day, and an extended release form (marketed as ER or XR) which is taken once a day.

Almost always, when people report diarrhea or intense heartburn with metformin, they are taking regular version. I experienced the heartburn on the regular drug. It was very disturbing because the pain was localized over my heart and felt just like the description of a heart attack you read in articles. My doctor assured me it was coming from the metformin, but that didn't make it any easier to live with because I kept wondering how, if I were having a real heart attack, I'd know it wasn't a pain from the drug?

The ER version releases the drug more slowly and this usually eliminates the gastrointestinal problems.

The trade off with taking the ER form is that the amount of blood sugar lowering you see might be a bit less than with the regular form as the drug acts in a slower smoother fashion rather than hitting all at once. But if you can't take the regular at all drug because of the side effects, the slight weakening in effect is a reasonable trade off. Plus, you only have to remember to take one dose rather than three. For me, this is not a trivial benefit. Even remembering to take one dose a day is sometimes a challenge!

One important point that my doctor missed when prescribing the ER version of metformin is this: The maximum dose of Metformin ER is LOWER than the maximum dose of regular Metformin.

According to the prescribing information, the maximum dose of the ER is 2000 mg a day. That of the regular is 2550 mg/day. Don't count on a pharmacist to catch the error if your doctor prescribes too much. Mine didn't, but I felt distinctly unwell on the high dose, and a quick look at the prescribing information online showed me the error.

Fortunately, a metformin overdose appears to be surprisingly benign. People have survived suicide attempts where they swallowed as much as 85 grams of the stuff at once. (They did develop lactic acidosis, which can be fatal, but survived.)

The dose at which metformin is supposed to be effective for most people is 1500 mg per day, though I know some smaller people who find a dose of 1000 mg effective. Your body weight will make a difference here, so if you are very large, you may need the maximum dose. In any event, don't conclude that metformin doesn't work until you have tested the dose up to the maximum.

It also takes up to two weeks for the full effect of metformin to become evident. While I will see an increase in my blood sugars if I forget a single day's dose, if I stop the drug for two weeks I see a slow rise in blood sugars through this period. My guess is that this two stage effect is because metformin works both on the liver (where it reduces the release of glucose) and the muscle (where it tricks the tissue into thinking it has just exercised and thus ramps up its burning of glucose). Whatever the explanation, give the drug a few weeks to see what it really does.

Also, many people who experience gas after taking metformin find that cutting way back on their intake of starchy carbohydrates helps eliminate the problem.

Because you only take metformin ER once a day you might wonder what happens if you take it a few hours earlier than usual. Will this cause a dangerous overlap? My experience has been that this isn't a problem. I suspect that the drug does not release evenly over the 24 hours it is supposed to act, and by 20 hours it is pretty much done, so there is no need to be obsessive about taking it at exactly the same time each day.

If I completely space out and don't remember to take the drug for 5 or 6 hours, though, I usually only take half my dose because that way when I take the normal dose at the usual time I don't have too much overlap to worry about.

I have found that there can be significant differences in how the different manufacturers' versions of generic metformin affect my blood sugar. The version I'm taking now, the 750 mg ER pill manufactured by Teva, does not seem to be quite as slow in releasing the drug as other brands are, so I get a much stronger effect during the day, but it wears off by the next morning. Other brands last better through the night, but I don't get anywhere near as good post-prandial numbers at lunch and dinner.

Not so coincidentally, the Teva version of metformin ER comes in a compact, flecked pink pill, while the other versions are pillowy white pills that appear to involve an indigestible matrix in which the drug is embedded. I suspect that the pillowy stuff works a bit better at slowing the digestion of the drug which makes the Teva version sort of a semi ER/semi regular version. That works for me.

I've tried splitting the dose to even out the response, however, I find that if I take Metformin in the evening I end up having to get up to pee at night more than usual. Since this is already a problem for me, I prefer to take it in the morning.

Finally, both Metformin and Metformin ER are currently available for a $4 copay at Wal-mart pharmacies offering the $4 copays on selected generics.