In early March, Esperion Therapeutics (NASDAQ:ESPR) reported data from the first of five trials evaluating its cholesterol-lowering drug, bempedoic acid. The data show it reduces bad cholesterol levels, but share prices fell because of safety concerns. On Tuesday, it appears those concerns are waning following data from a phase 2 trial evaluating its use alongside PCSK9 inhibitors in patients with hypercholesterolemia.

A big market opportunity

Tens of millions of people take statins to help control bad cholesterol (LDL-C), yet many of those patients still fail to lower their bad cholesterol levels to target levels and about 600,000 Americans die because of heart disease every year.

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Given the size of the market and the need for more effective cholesterol-lowering medications, drugmakers have been working hard developing drugs that work in new ways. The new drugs may help patients who are still shy of their cholesterol goals despite using statins or can't take statins because of their side effects.

Most of these efforts have failed, but in 2015 Amgen Inc. (NASDAQ:AMGN) and Regeneron Pharmaceuticals (NASDAQ:REGN) launched two new drugs -- Repatha and Praluent -- that target LDL-C in an entirely new way. They inhibit a gene responsible for breaking down bad cholesterol receptors in the liver so that more bad cholesterol can be removed from the bloodstream. In trials, these PCSK9 biologics lowered bad cholesterol by an additional 60% when added to statins.

Although PCSK9 inhibitors are effective, they're injected, complex biologics that can cost $14,000 per year. Those drawbacks arguably make them less than ideal for widespread use.

Esperion Therapeutics bempedoic acid is a small-molecule drug that can be produced cheaply and taken daily as a pill, so it may be a better solution. That's especially true if a single tablet combination with Lipitor and another widely used cholesterol drug, Zetia, makes it to market.

On March 7, bempedoic acid took an important step toward FDA approval when results from its first phase 3 trial were unveiled. In that study, adding bempedoic acid to Zetia in statin-intolerant patients lowered bad cholesterol by an additional 23%. Those results were similar to what was observed in bempedoic acid's mid-stage trials.

Despite its efficacy, Esperion Therapeutics' shares fell because elevated liver enzymes were observed in two patients, or 1.1% of participants. That rate was concerning because elevations in liver enzymes greater than three times the upper limit of normal occurred in only 0.7% of patients in large-scale Lipitor studies.

While the safety concern shouldn't be dismissed, I previously wrote that across the 919 patients participating in phase 2 or phase 3 trials, elevated enzyme levels above three times the upper limit of normal were observed in only 0.65% of people. The lower ratio suggests investors might not want to draw too many conclusions from the single phase 3 study.

On Tuesday, management reported phase 2 trial data that was less concerning. In the trial, adding bempedoic acid to PCSK9 inhibitors reduced bad cholesterol by an additional 27%, and importantly there weren't any patients in the study who had elevations in liver function tests of greater than three times the upper limit of normal. Following those results, elevated levels greater than three times the upper limit of normal have only been observed in 0.63% of the 947 people who've participated in the phase 2 and phase 3 studies that have been reported so far.

More data on deck

The latest study results are intriguing because they demonstrate that, if necessary, bempedoic acid can be used alongside PCSK9 inhibitors. However, what makes this trial really important is the solid safety data. If the safety results in the remaining phase 3 trials don't raise anymore eyebrows, than Esperion Therapeutics could be on track to have a blockbuster drug on its hands. That said, there's no guarantee that the upcoming trials will read out positively and that does make this a risky stock to buy. Therefore, investors might want to approach it a bit cautiously until more data is in hand. That shouldn't be too long of a wait. Results from two phase 3 trials are expected in May.

Todd Campbell owns shares of Amgen and Esperion Therapeutics. His clients may have positions in the companies mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.