Cempra Inc.’shares surged 38 percent Friday morning after the clinical-stage drug maker said that its pill to treat acute bacterial skin infections cleared a late-stage study, inching the company one step closer to getting its first drug to market.

This is Cempra’s best ever one-day percentage gain, showing a return of investor optimism two months after the U.S. Food And Drug Administration rejected the company’s pneumonia antibiotic.

Cempra said the fusidic acid drug from its most recent study was found as effective as the generic oral antibiotic, linezolid, to treat patients with serious acute bacterial skin infections.

ABSSSI, as the bacterial skin infections are called, leads to more than 5 million hospitalizations each year in the United States and Western Europe.

The drug has been used in Europe for decades. Often prescribed topically in creams, it stops bacteria from reproducing.

Pfizer originally developed linezolidone, and the Medicines Co’s Orbactiv, Merck & Co’s Sivextro and Allergan Plc’s Dalvance and Teflaro are already approved to treat the condition.

Cempra is attempting to enter a crowded market that’s not as profitable as other markets such as the treatment of cancer, but the need for new antibiotics is mounting as patients build up resistance to older therapies.

Cempra said the rate of side effects seen in the trial was similar across both treatment groups, and that it plans to meet with the FDA to plan a path for fusidic acid’s approval.

The company is also studying the potential to use the drug to treat bone and joint infections.

In December, Cempra’s antibiotic to treat community-acquired bacterial pneumonia was rejected by the FDA, due to manufacturing issues and inadequate data about the damage the drug does to the liver.

Most analysts said Cempra would likely abandon the drug after the FDA recommended testing the drug on another 9,000 patients. The company had tested it on 920 patients.

Shares of Cempra were trading at $4.22 as of noon Friday, up 34 percent.