When best-selling cholesterol drug Lipitor fell off the patent cliff in 2011, the question became, "What's next?" A hot new class of treatments called PCSK9 inhibitors want to become the answer. Sanofi (NYSE: SNY ) and Regeneron (NASDAQ: REGN ) lead the pipeline projects, with Amgen (NASDAQ: AMGN ) a close second. Pfizer (NYSE: PFE ) -- the former home of Lipitor -- pulls up the rear with Roche. What's the fuss? Could these drugs unseat statins like Lipitor? Market potential PCSK9 inhibitors won't replace statins. Statins work too well for the majority of patients, offer a low price tag, and a convenient oral dosage. Most of the PCSK9 drugs are injectable and biologics, which means they'll carry a hefty cost. The best chance will come from targeting those patients who can't find sufficient treatment in statins. Hypercholesterolemia patients have high levels of LDL -- or "bad" cholesterol -- due to either a genetic condition or lifestyle choices. Patients with genetic conditions tend to have cholesterol levels that require something more potent. About 10% of general cholesterol patients have statin intolerance, and others need a bit more help than what statins provide. These patient groups will form the market for PCSK9 inhibitors. With those caveats in mind, let's move on to the lead contenders. Leaders of the pack Regeneron partnered with Sanofi on REGN727, and phase 3 trials initiated last summer. Sanofi hopes to push the drug through the Food and Drug Administration in 2015. Mid-stage trial results showed an LDL reduction of 40% to 72% in patients already taking Lipitor. That range, which covers low and high dosages, compares favorably to the 5% reduction with placebo. Patients with the genetic condition heterozygous familial hypercholesterolemia (heFH) had drops of 28.9% to 67.9% compared to 10.7% with the placebo. Amgen has AMG 145 gearing up for phase 3 trials with the goal of finishing the regulatory process in 2015 -- right on REGN727's heels. In mid-stage trials, AMG145 tested alone and in conjunction with Merck's (NYSE: MRK ) Zetia. Amgen's drug lowered LDL levels 51% at the highest dose on its own and 63% with Zetia. That's compared to a 15% reduction with Zetia alone. AMG 145 combined with statins caused a 56% reduction in heHF patients. Bringing up the rear Pfizer released some early data on a small trial for RN316 that showed 56% reduction in patients already on high doses of statins. But even Pfizer admits the data's misleading because patients falling below a certain cholesterol level had to discontinue treatment for safety purposes. Roche should finish phase 2 this year for its hushed PCSK9 inhibitor RG7652. The company had a high profile failure with its cholesterol drug dalcetrapib, which flunked out of late stage trials. It will be quite some time before these projects provide solid data. Arriving late to the market will allow these drugs to see how the first batch fairs in the market. Foolish final thoughts Out of the developers, Regeneron has the most at stake with the smallest pipeline. But it has a winning drug and Sanofi's backing. Time will tell how much these drugs will earn, but it's safe to say the numbers won't reach Lipitor levels. As Brian Orelli noted, PCSK9 inhibitors would need to beat statins not only on lowering cholesterol but also reducing heart risks. Cardiovascular outcome trials take a lot of time and could offer insufficient data. These drugs have merit but will likely stay in the at-need patient subsets for the near future.