(Reuters) - Tetraphase Pharmaceuticals Inc said its lead experimental antibiotic for serious bacterial infections met the main goal in a late-stage study, sending its shares surging nearly 23 percent in after-market trading on Tuesday.

The company said the antibiotic, eravacycline, was being studied in a pivotal 500 patient late-stage study for intra-abdominal infections.

Tetraphase said the drug showed statistically significant improvement in curing patients with intra-abdominal infections, compared to patients who were treated with Medicines Co’s drug, meropenem.

Eravacycline is a synthetic tetracycline derivative for drug-resistant bacterial infections administered intravenously in hospital.

The company plans to submit a marketing application for the drug to the U.S. Food and Drug Administration by the first quarter of 2018.

Tetraphase expects to also apply for European approval by the third quarter of this year.

The company’s shares were up about 20 percent at $8.25, making them the top percentage gainer among Nasdaq-listed stocks in extended trading.

Up to Tuesday close of $6.90, the stock had gained about 71 percent this year.