If you're over the age of 45 and are at risk of heart disease, your doctor may start recommending you take statins like Pfizer's (PFE 2.40%) Lipitor, Merck's (MRK 0.44%) Zetia, or AstraZeneca's (AZN 0.28%) Crestor. Those drugs are part of a class of cholesterol fighting compounds known as statins that are already being prescribed to roughly a third of U.S. adults. 

In November, guidance provided to doctors by the American Heart Association recommended the use of statins be expanded from those already showing signs of heart disease to those that may also be at risk of developing heart disease based on factors like weight, age, and blood pressure.

That shift in guidance may increase the number of patients taking statins to nearly half of all U.S. adults. However, the benefit of this change may not be limited to the manufacturers of statins. It may also eventually boost the use of next-generation cholesterol fighting compounds being developed by Regeneron (REGN 0.32%), Amgen (AMGN 2.35%), and Pfizer.

Curbing cholesterol
According to research published in the New England Journal of Medicine, statins may be prescribed to 12 million more people following the revamped guidance. More than 10 million of those 12 million are likely to be people who have no cardiovascular disease currently, but may have heart disease in the future. 

The biggest impact will be among those aged 60 and up. Under the previous guidelines, roughly 30% of those in that age group were deemed eligible for statin therapy. Now, more than 80% will be considered eligible.

That's a huge increase in the patient population served by these medications, and it may mark the biggest shift in their use since they were first approved in the 1990s. But what do statins do?

Cholesterol is important to a body's normal functioning. It's a necessary building block for every cell in our bodies. But sometimes, cholesterol can build up in the wrong places, like our arteries. If those buildups become blockages, patients can suffer a stroke or heart attack.

So, while some cholesterol is necessary, controlling "bad" cholesterol, or LDL, can help prevent those dangerous buildups. To do this, drugmakers developed statins. Statins encourage the liver -- the organ responsible for creating 70% of our body's cholesterol -- to remove LDL from the bloodstream by reducing the production of a cholesterol creating enzyme. In studies, statins successfully lowered the amount of bad cholesterol enough to reduce the chance of heart disease by 60%. 

Based on that success, doctors turned statinsinto the most widely sold treatments in America, resulting in more than $20 billion in annual sales for statin drug manufacturers at their height. 

A maturing market for statins
The most successful statin of all-time was Pfizer's Lipitor. Lipitor was the most widely prescribed statin in the U.S., and the top-selling drug of all time. Lipitor generated more than $125 billion in sales for Pfizer between 1997 and 2011,and prior to losing patent exclusivity, Lipitor's sales were eclipsing $12 billion a year.

But Lipitor isn't the only statin that ranks among the best-selling therapies. According to IMS, Merck's Zetia, for example, is the 28th best-selling drug in the U.S., with sales of $444 million in the fourth quarter.Zetia's total global sales were $2.7 billion;however, that pales in comparison to AstraZeneca's Crestor.

Crestor's sales totaled $1.5 billion in the fourth quarter, bringing sales of Astra's cholesterol fighter to $5.6 billion last year. That made Crestor the fourth best-selling drug in America in 2013, according to IMS.

A lot of soon-to-be prescribed statin users will likely find themselves treated with generic versions of Lipitor, but some will end up with prescriptions for Zetia or Crestor instead. That suggests sales for both drugs may climb in the coming year.

Developing the next cholesterol busting drug
Statins have been widely used, but they don't work for everyone. In some cases, patients don't respond to the therapy, and in others, side affects like memory loss or muscle weakness may occur.

That has drug developers hard at work developing drugs that can either replace or improve statin therapy. The most advanced of this research centers around the PCSK9 gene.

Statins have been shown to boost the amount of the PCSK9 protein created by that gene, and PCSK9 protein has been associated with reducing statin's effectiveness. As a result, companies including Regeneron, Amgen, and Pfizer are conducting trials across thousands of patients for PCSK9 inhibiting therapies.

Both Regeneron and Amgen's drugs are closest to convincing regulators to approve their use. Regeneron, which is working with Sanofi on the new drug, reported its alirocumab PCSK9 drug reduced bad cholesterol in 94% of patients during phase 3 trials. On average, patients treated with alirocumab saw their LDL levels fall by 47% after 24 weeks.

During phase 2 trials, Amgen's PCSK9 drug, labeled AMG-145 or evolucumab, reduced bad cholesterol by 40% to 59% versus just 0.1% to 0.5% for patients treated with placebo. While Amgen hasn't released the exact numbers for its phase 3 trials, it has indicated it saw similar results.

Over at Pfizer, its PCSK9 compound, RN316, is similarly successful, lowering LDL by 56% after 12 weeks. 

Fool-worthy final thoughts
The American Heart Association estimates Americans spending on cardiovascular disease will triple by 2030 to more than $800 billion as the number of people with the disease grows to roughly 40% of the population.

In order to control that spending, doctors will have to proactively treat patients that are at risk of developing the disease. While a lot of that activity will center on promoting healthier lifestyles, many will also turn to statin therapy.

Assuming Regeneron, Amgen, and Pfizer are able to usher their new PCSK9 drugs to market, those drugs may soon be prescribed alongside, or instead of, statins in some cardiovascular patients. Of course, not every patient will benefit from the increased use of these drugs, but for many, their use may prove life-saving. After all, heart disease is responsible for roughly one in four deaths every year.