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A month’s supply costs you about the same as a Starbucks latte. It’s one of the oldest drugs in active clinical use today, and it’s now the first-line drug for almost everyone with newly diagnosed Type 2 diabetes on the planet. Most of the millions of people who take it don’t give it a second thought, but humble metformin may well be the closest thing we have to a miracle drug.
Consider the following: Other than insulin, metformin packs probably the biggest blood-glucose-lowering punch of any diabetes drug on the market, lowering HbA1c levels (a measure of blood glucose control) by up to 1.5%. It protects your heart, and it might even hold some cancers at bay. It gets along well with a wide variety of other drugs and treatments, and by most measures, it’s safer than most other prescription drugs. Impressively, it’s risen from the ranks of a “me-too” drug (a drug that’s very similar to an existing drug) to the very pinnacle of diabetes treatment worldwide.
What do you know about this unsung hero among diabetes drugs? Check out this “biography” of metformin to learn everything you ever wanted to know, but were afraid — or didn’t even know — to ask.
The birth of metformin
Like most drugs, metformin has its roots in a plant — in this case, the French lilac (Galega officinalis). Research into this plant’s potential as an antidiabetic agent dates back to the early 1920’s, but major efforts were abandoned with the discovery and development of insulin. It wasn’t until 30 years later, in the search for oral drugs to control diabetes, that these efforts resumed. While the French lilac has long been known to have glucose-lowering properties, it has also long been known to be poisonous. Because it is dangerous to livestock, here in the United States it’s listed as a noxious weed in 12 states, including pretty much every state it grows in.
And just how does metformin lower blood glucose? No one knows, despite the fact that it is one of the most studied compounds in the world, having been the subject of over 13,000 clinical researchers and more than 5,600 published studies over the last 60 years. The leading theories on metformin hold that it limits glucose production in the liver, or that it helps muscle tissue take in glucose. Or that it helps with carbohydrate absorption. Or that it’s a mild insulin sensitizer. It’s probably a combination of all of these factors, although this is far from a definite answer.
But metformin does work, and it works fast, nearly from the first pill. It also carries little risk of overdoing its job; when used alone as a treatment, metformin rarely causes hypoglycemia (low blood glucose). It does not cause weight gain, and in many people it causes mild weight loss. It reduces the risk of heart attack, can be combined with other blood-glucose-lowering drugs, and has few harmful side effects. (Click here to learn more about the side effects of metformin.) Yet in the beginning, metformin was nowhere near as beloved as it is today.
Fears of lactic acidosis, a wickedly dangerous side effect from some members of the biguanide family of medicines, of which metformin is a part, delayed its approval by the Food and Drug Administration (FDA) in the United States until 1995 — fully 38 years after the drug’s deployment in Europe. Lactic acidosis is a metabolic crisis in which the blood becomes acidic. It frightens doctors and patients alike because of its reputation as a one-way street, with an overall mortality rate above 75% and a median survival time of only 28 hours.
But what’s the risk of lactic acidosis from metformin, really? Cartoon character SpongeBob SquarePants may have said it best in the famous episode on sea bears: “Sea bears are no laughing matter. Why once I met this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy, who knew this guy’s cousin…” Like sea bears, very few doctors have actually seen a case of metformin-induced lactic acidosis with their own eyes. But these rumors and hearsay kept prescriptions low during metformin’s early years in the United States, despite its already long clinical career in Europe.
But now, after 50 years in the trenches, we know just how safe metformin really is. At the very worst, the rate of lactic acidosis associated with metformin is 3 cases per 100,000 patient-years. And on those exceptionally rare occasions when lactic acidosis is seen in metformin users, the fatality rate appears to be much lower than is usually seen when other drugs or conditions cause lactic acidosis. By comparison, the arthritis medicine celecoxib (Celebrex) carries an associated all-cause mortality rate of 1,140 per 100,000 patient-years.
But does metformin really cause lactic acidosis at all? One recent study, first published in the Cochrane Database, looked at pooled data from 347 recent clinical studies. In all of these clinical studies, there were no cases of lactic acidosis among participants who were assigned to take metformin. The new study also points out that people with diabetes are more prone to lactic acidosis than the general population in the first place. Other studies have shown that rates of lactic acidosis in non-metformin arms of clinical studies are actually higher than in metformin arms, seriously calling into question the conventional wisdom that metformin causes lactic acidosis.
Why, then, has this fear been so widespread? Metformin actually wasn’t the first member of the biguanide family of drugs to hit the market. It was preceded by buformin and by phenformin, which is now banned nearly everywhere. In contrast to metformin’s theoretical lactic acidosis rate of 3 cases per 100,000 patient-years, phenformin had a rate more than 20 times higher. It was pulled from the market following a number of high-profile deaths in France in the 1970’s.
By the way, even if metformin does cause lactic acidosis, it’s not the only cheap pill to do so. Lactic acidosis is also associated with overdoses of acetaminophen, more commonly known by its brand name, Tylenol.
Metformin makes it big
So how did metformin achieve this career transformation? It wasn’t until the UK Prospective Diabetes Study (UKPDS) was released in 1998 that the floodgates of acceptance opened. The UKPDS gave American doctors solid clinical evidence of metformin’s effectiveness at both lowering blood glucose and improving cardiovascular outcomes, just at the time when medicine in the United States was moving to a more evidence-based framework. Metformin began to pick up speed, and it hasn’t really hit any stumbling blocks since then.
According to the IMS Health National Prescription Audit, more than 59.1 million prescriptions for metformin were dispensed in the United States alone in 2011. If you’re wondering how 18.8 million people with diagnosed diabetes can use three times as many prescriptions, it’s because each time someone refills a 30- or 90-day supply of metformin, it counts as one prescription. Still, that’s a lot of metformin. Even at a measly four bucks a pop, the drug grosses nearly a quarter of a billion dollars per year in the United States alone. And globally, metformin is the most widely prescribed diabetes drug. Its father, Dr. Sterne, would be proud.
Metformin gets married
Metformin has been combined in diabetes polypills with sulfonylureas (in Metaglip, Glucovance, Amaryl M), thiazolidinediones (ACTOplus met), and DPP-4 inhibitors (Janumet, Galvumet, Kombiglyze XR). Globally, there are now more than 20 polypills containing metformin, and the list is likely to continue to grow as new diabetes drugs are developed.
The most commonly prescribed extended-release version of metformin is Glucophage XR. This pill accomplishes its mission with a polymer that turns into a gel in the stomach, which blocks quick absorption of the medicine. This XR formulation has been shown to prolong the absorption of the drug to a peak of around seven hours, compared with traditional metformin’s three-hour peak in working action.
Indian researchers are currently experimenting with a floating pill that would stay in the stomach for even longer, slowly releasing metformin the entire time. For as long as metformin remains a popular diabetes drug, it is a safe bet that researchers will be trying to create new and innovative ways to deliver it to the body.
A promising future
Beyond diabetes, metformin is an effective treatment for polycystic ovary syndrome (PCOS), for which it can increase ovulation rates fourfold. While it is not FDA-approved for this use, metformin features prominently in the treatment guidelines for PCOS of many organizations worldwide, including the American College of Obstetricians and Gynecologists. In the area of HIV/AIDS treatment, metformin is sometimes used to reduce cardiovascular risk factors. And far on the cutting edge of medical research, metformin is being evaluated for its potential to reduce the growth of tumors.
Closer to its original home, metformin is increasingly used in efforts to prevent Type 2 diabetes, or at least to delay the onset of full-blown diabetes in people with prediabetes. Although metformin is not FDA-approved for prediabetes, more and more doctors prescribe it to keep blood glucose levels in the normal range for as long as possible.
After more than 50 years, it is safe to say that metformin is still going strong.
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