Another setback for Cempra’s solithromycin, this time in gonorrhea

After being hit with an FDA complete response letter for its late-stage effort solithromycin at the end of last year, Cempra has quietly announced another setback in its financial results today after the drug came up short in a gonorrhea test.

Cempra says it has combed through data from an initial patient cohort of 262 patients in the so-called SOLITAIRE-U phase 3 study, which was geared to look how a single 1000-mg dose of oral solithromycin fared in uncomplicated genitourinary gonorrhea (GC), with or without concomitant chlamydia infection, compared with an injected antibiotic ceftriaxone alongside an oral antibiotic, azithromycin.

Cempra said it saw high success rates, especially in women patients, but so did the older meds, and in the end the data showed it did not hit the relatively low bar of noninferiority compared to these treatments.

But the biotech, which had some better news last week, is still planning on trying to make its next-gen macrolide work in this disease setting.

“We believe that the small number of solithromycin treatment failures observed in SOLITAIRE-U could be reduced in an approval-enabling study with an adjustment to the dosing regimen, as we believe the treatment failures were most likely related to the duration of study drug exposure at the site of infection,” it said in a statement.

“We plan to discuss our next steps with the GC program with NIAID and the FDA, as resistance to existing therapies for GC has created an urgent unmet medical need. In SOLITAIRE-U, no GC isolates demonstrated solithromycin resistance at baseline, and there was no emergence of solithromycin resistance in the isolates obtained at follow-up cultures.”

In December, the biotech was hit with an FDA complete response letter for both the oral and intravenous forms of its drug, something that will likely mean a lengthy delay for any approval of solithromycin in community-acquired bacterial pneumonia (CABP) in adults.

The first issue was safety: The FDA said it was concerned over potential liver injury from the drug, saying “hepatotoxicity had not been adequately characterized.”

The FDA said the size of the safety database on this issue was limited to 920 patients who received solithromycin, but said this was “too small to adequately characterize the nature and frequency of serious hepatic adverse effects.”

So, Cempra will need to undertake a study of around 9,000 patients who have been exposed to solithromycin in order to see whether the drug is hitting patients’ livers.

On top of this, a “comprehensive plan for post-marketing safety assessment including an enhanced pharmacovigilance program would also be required,” the FDA said in relation to hepatotoxicity. This drove its shares down 40% on the day.

Its latest setback in testing will only add to its headaches: It was down 18% on the news this morning.