Iterum Therapeutics filed to raise $92 million in an IPO that will support the phase 3 clinical trials of oral and intravenous versions of the antibiotic sulopenem.

Sulopenem is in the same class of antibiotics as penicillin. Pfizer offloaded the drug to the Dublin-based biotech in 2015 in exchange for an upfront payment, a stake in Iterum and the chance to receive additional equity, milestones and royalties later on.

Intravenous sulopenem is active against the gram-negative bacteria that cause urinary tract and intra-abdominal infections, the company says. Gram-negative bacteria are resistant to multiple drugs and are becoming increasingly resistant to approved antibiotics. Iterum tweaked Pfizer’s oral prodrug, sulopenem etzadroxil, by adding probenecid and combining them into a single tablet.

"We plan to initiate a Phase 3 clinical program in the second half of 2018 for the treatment of adults in three indications: [uncomplicated urinary tract infection], complicated urinary tract infections (cUTI) and complicated intra-abdominal infections (cIAI)," Iterum said in an SEC filing. It expects topline data to read out for all three trials in the second half of 2019 and plans to file NDAs by the end of 2019.

In addition to funding its phase 3 program, the capital is earmarked for working capital, paying down debt, making license payments to Pfizer and "other general corporate purposes" which may include "regulatory, manufacturing, clinical supply and related costs," according to an SEC filing. The IPO comes a year after Iterum raised $65 million in series B funding.

Pfizer abandoned sulopenem in 2010. Data presented that year linked two regimens of sulopenem to cure rates of 90% and 88% in patients with community-acquired pneumonia requiring hospitalization, while patients who took a different antibiotic combo—ceftriaxone followed by an amoxicillin-clavulanate suspension—had a cure rate of 63%.

The trial failed to show a statistically significant difference between the sulopenem and control arms. But Pfizer enrolled only 33 patients in the trial, fewer than originally planned, and 10 dropped out, making it difficult to draw concrete conclusions.

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