Metformin

metformin

As I was considering which diabetes drug to feature in my first ‘drug post,’ there was only one clear choice.  The most prescribed medication for diabetes, and one that literally hundreds of my patients use is…metformin!  Metformin is the generic name.  Some of the brand names you may be familiar with are Glucophage, Glucophage XR, Fortamet, and Riomet (the liquid form of metformin).

Just a heads-up, remember that I am a pharmacist.  So, when describing a drug, I will sound like, you guessed it, a pharmacist.  Blame my training.  I’ll try to make things simple and easy to follow and understand, but if I’ve ever gone too “scientific” and you’d like things explained another way, or you have questions, feel free to let me know.  My email will be available at the end of my post.  An important thing to remember before I start: glucose is just a fancy name for sugar.  I’ll probably use glucose because it is most common for me, so just don’t be confused by my terminology – I am referring to sugars.  So without further ado…metformin!

Metformin – How It Lowers Blood Glucose

Something for you to remember: as a diabetic you have sugar (glucose) in your blood – kind of floating around your cells because for some reason it’s not getting into them.  Sugar in the blood and not in the cell is a bad thing.  Normally insulin in your body helps sugar enter your cells, but in diabetics it just isn’t doing the trick.  Metformin makes your cells more sensitive to allowing sugar to enter – kind of like opening the door for sugar.  More sugar in cells means less floating around in your blood, which means lower A1c, which makes for a healthier person.

Is that enough?  Ok, so now sugar is going into your cells where it belongs, so we have a perfectly wonderful drug for diabetes and can be happy with that.  Do you think that the scientists that made metformin thought that?  You guessed it, of course they didn’t!  They wanted more “bang for their buck,” so they thought of another way to keep sugars out of your blood.  How did they do that?  By not allowing it into your blood in the first place.  Metformin is very special – it acts as a sort of bodyguard after you eat a meal.  Metformin helps to keep some of the sugars that you eat from entering your bloodstream.  If the sugars stay in your stomach and intestines and don’t enter your blood, the result is lower blood sugar readings.  Pretty simple, huh?

But wait, there’s more!  Would you believe it – your body actually produces it’s own sugar!  You see, our bodies need a certain amount of sugar for energy.  Your brain lives off of it, as do many other important organs.  So your liver has the important job of making sugar when needed.  Unfortunately in diabetics, it will do this sometimes even when you have enough already in your blood.  So for that reason, the makers of metformin decided to develop their drug so that it would stop the liver from producing that extra sugar.

Look at that – three different ways that metformin helps with diabetes!  No wonder it is the drug that is chosen first for most new type 2 diabetics.

Metformin – The Effect on Your Numbers

So where does that put us?  How does this change the numbers you are seeing on your blood tests?  With metformin, you can expect to see a decrease in your A1c of at least 1-2% (example: your A1c could decrease from 10 down to 8 or 9 after metformin is started).  Remember that A1c tells the story of your average blood sugars over the past 3 months.  You could look at the blood sugar readings that you take during the day as photographs, whereas your A1c would be the title of the photo album.

An added bonus of metformin is that it might help to lower your bad cholesterol and increase your good cholesterol.  There is a potential for modest weight loss when on metformin, but the average is only about 2.6 pounds, so it is not a “miracle” weight loss drug.  However, it is unique because it is a diabetes medication that is weight neutral, meaning it does not cause weight gain.  As you will learn later, this is not the case with all diabetes medications.

Metformin – Dosing

Initially, most patients are started at doses of 500 mg once or twice daily of the immediate release (IR) form of metformin.  Immediate release just means that the medication enters your blood all at once, versus slowly releasing all day long (extended release).  If a patient is new to metformin and is starting at a dose of 500 mg twice daily, I usually recommend starting at 500 mg once daily for the first three days in order to decrease stomach upset.  There is a less commonly used 850 mg dose of metformin that is available, which is started at one tablet daily with breakfast.

For some patients, extended release (ER) metformin is chosen.  Metformin ER enters the blood more slowly, which leads to less stomach upset and discomfort.  Since metformin ER only needs to be taken once daily, it is a good choice for patients that have trouble with taking a medicine twice daily (can’t remember, varied schedules, etc).  Patients are generally started on 500 – 1000 mg of metformin ER, taken with the evening meal.  Do not cut, crush, or chew metformin ER because it is specifically made to disperse throughout the day, not all at once.

Because of unpleasant stomach upset and side effects, metformin should always be taken with food or immediately following the meal.  We start metformin at low doses because of the high potential for side effects.  Doses are then increased weekly if needed.  Generally we do not see a response with metformin at doses less than 1500 mg per day, so don’t be discouraged if your doctor keeps increasing your dosage.  It may take up to eight weeks of being on metformin before full effectiveness can be seen, so patience really is a virtue.

Metformin – Side Effects

I have already previewed the major side effect of metformin, which is stomach upset.  This includes diarrhea, nausea/vomiting, and gas.  As I mentioned, taking the medication with meals and increasing doses slowly over days and weeks can help to minimize this.  When starting metformin, patients sometimes complain of an unpleasant or metallic taste.  This tends to go away within the first few weeks.  More rarely we see skin rashes, itching, and sun sensitivity (sunburning easily) with metformin use.

A very rare (2-10 patients per 100,000 patients on metformin per year) but serious side effect that is caused by metformin is something known as lactic acidosis.  Lactic acid is a part of our metabolism that helps us produce energy when we do things like exercising.  At high levels, it can be very dangerous.  Lactic acidosis can be deadly in up to 50% of cases.  If lactic acid levels are too high, dialysis is required to remove the metformin from the body and to correct the increased lactic acid levels.  Fortunately physicians and pharmacists are well aware of this side effect, and it is easily preventable if certain patients that are more at risk are not given metformin.  Side effects from metformin are very rare and can be easily dealt with and prevented by taking the medicine with food and switching to a different medication if needed.

Last week I had a patient that was switched from metformin to glipizide.  While her A1c was okay, her kidneys were not doing very well, which could lead to lactic acidosis.  So, her doctor changed her to another medication.  This leads me into a discussion of which patients would not be eligible to take metformin.

Metformin – Who Should Not Take It

Patients with kidney disease or kidney failure are more at risk of developing lactic acidosis, since metformin is removed from the body solely by the kidneys (if your kidneys are not good, metformin stays in your body too long, causing problems).  Your doctor will do blood tests to determine the health of your kidneys prior to starting you on metformin.  If your kidneys are not healthy enough, another medication will be used.  As we get older, our kidneys generally do not work as well, so metformin is not recommended in anyone over the age of 80 years old, unless your doctor determines that your kidneys are healthy.

The liver is responsible for regulating lactic acid levels in our bodies, so anyone with liver disease should avoid metformin.  Since alcohol has a negative effect on the liver, patients should be advised not to drink in excess (binge drinking, or chronic use of more than two drinks per day or at one sitting).  I’m sure that the other effects of alcohol on diabetes will be covered in a future blog post.

Metformin – Drug interactions  

Certain stomach medications used for acid reflux (cimetidine – generic for Tagamet, and ranitidine – generic for Zantac) interact with metformin.  Two antibiotics (cephalexin – generic for Keflex, and Bactrim) may increase metformin concentrations.  You would think that this is a good thing, but it can lead to more harm than good (increased side effects, stomach discomfort and pain).  The fluoroquinolone antibiotics (Levaquin, Cipro) may cause increases or decreases in blood glucose levels, which are also not good things for diabetic patients.  There are other medications that I have not included on this list, for sake of space, so please remember to check with your pharmacist or physician, and make sure they are aware of all medications you are taking.

I know this is lot of ‘pharmese’ so far, but I am a pharmacist so what do you expect? Bottom line is that you need to always let your doctor and pharmacist know what drugs you are taking so any negative interactions can be avoided.  Don’t forget to ask your pharmacist to check for interactions before you stop to pick up a product from the cough/cold or vitamin section of the pharmacy, because these are also medications and they can interact with other things you are taking.  Your doctor and pharmacist should be informed about all prescription and over-the-counter medications that you are using, as well as any allergies you have to medications.

Some folks have more than one doctor – always let all doctors know every medication you are on.  And, use only one pharmacy so they can check for interactions.  You run risks if you use more than one pharmacy – nobody knows all of the drugs you are taking, so you don’t have a safeguard in place.  So to sum up: make sure all doctors know about all of your medications, and use one pharmacy.  Okay?  It’s best for you that way.  I’ll step off my soapbox now.

Metformin – Monitoring

Sometimes I have patients ask me why they have to make another appointment with their doctor before they will be given any refills.  “I’m a diabetic, and I will be for the rest of my life.  Why do they need to see me every year?  Aren’t they just going to keep me on my meds?”

This is a very valid question.  As you can see from what I’ve been talking about in this post, there are many reasons why metformin (or any other medication) might not be appropriate for a patient.  And, our bodies are always changing – what might have been the right medication and dosage for you when you started it might not be appropriate six months or even ten years later.  Your kidneys and liver might not be working as well to clear the medication.  Your control on diabetes might have improved or, sadly enough, gotten worse.

So at least once yearly, your physician will want you to come in for simple blood testing.  This will include a serum creatinine (something that gives us an idea of how well your kidneys are functioning), fasting plasma glucose and A1c (remember the photos and photo album?), and other blood components.

The ADA recommends A1c tests twice a year and a full panel of blood tests once a year. Your doctor should be following that as a minimum.  In the early stages of treatment, your doctor might test more often to track progress.  And, really, how long does a blood test take?  Most labs now allow you to make an appointment online so it’s faster and more convenient for you.  Sometimes you don’t even need to see the doctor – you get lab work and they send in the prescription once they have the results.  It’s as simple as that.  But remember, if they do need to see you, please make the appointment.  They really are only trying to make sure they have the right medication and dose for you, and that your diabetes is being taken care of properly.  We all want you to live a long and happy and enjoyable life.

Metformin – Place in Diabetes Therapy

Metformin is known as the cornerstone for treatment of type 2 diabetes.  The current guidelines that we follow when treating new diabetics state that metformin should be started before any other medication, unless the patient is not able to take it for the few reasons I stated earlier.  Metformin is also the only medication that is currently approved for use in pre-diabetics to prevent full-blown diabetes.  It is also the only oral diabetes medication approved for use in kids (age 10 and up).  Since insulin is the only other diabetes medication that can be used in kids right now (and let’s face it, what kid wants to get a shot?!), it is a very popular medication for those very young diabetics.  Unfortunately it does not work for type 1 diabetes, which is generally diagnosed in younger people.

If you would like to read more about metformin, here is another good website: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000974/

So there you have it, a review of our most popular diabetes medication, metformin.  Next week I will move on to one of the different categories of meds that we use to treat high blood sugars, so you will want to stay tuned.

As a disclaimer, I am your “virtual” pharmacist, here to provide you with information and answers to questions.  However, I am not your local pharmacist and could, in no way, be aware of your specific medical needs.  Remember to always check with your medical provider and pharmacist before stopping or starting any new medications.  My posts are based on general pharmacy principles and should not considered as your “first opinion” when it comes to your health.  Please consult with your doctor and pharmacist about anything regarding your health.

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