Sanofi and Regeneron had high hopes for IL-6 inhibitor Kevzara's chances as a repurposed therapy for COVID-19 patients after anecdotal results in China showed promise. But now, the drug has hit an early hurdle in the U.S. Will Kevzara go on to find its footing in phase 3? 

Sanofi and Regeneron will scale back a late-stage trial of Kevzara after its phase 2 precursor showed negligible results in treating "severe" COVID-19 patients requiring oxygen therapy, but not more intensive treatment, the drugmakers said Monday. 

The phase 3 stage of Kevzara's U.S. coronavirus program will now include only patients rated as "critical," meaning they require ventilation or ICU care. The phase 3 trial will also strip out  a 200-mg dose, which showed little efficacy at the phase 2 stage. 

In the phase 2 trial, preliminary data showed intravenous Kevzara lowered C-reactive protein in both severe and critical patients, an inflammation biomarker found at high levels in some COVID-19 patients. However, clinical outcomes in the severe arm of the study––including lowering the risk of ventilation and death––showed "negative trends" compared with positive outcomes in the critical arm, the drugmakers said.

Most confounding for Sanofi and Regeneron, those negative results in severely ill patients didn't carry over into the ongoing phase 3 study, where preliminary outcomes were "better than expected," they said. Still, after an independent data monitoring committee recommended the trial changes, no additional severe patients were enrolled. 

RELATED: Sanofi, Regeneron hustle Kevzara into 2nd pivotal coronavirus study

The phase 3 U.S. study continues to enroll critical patients, though, the drugmakers said. The aim is to eventually treat around 600 of them. Early results from that study are expected in June. 

Meanwhile, the drugmakers are still awaiting results from a phase 2/3 study of COVID-19 patients abroad. The ex-U.S. Kevzara trial, which dosed its first patient in late March, will enlist severe or critically ill patients who've been hospitalized in Italy, Spain, Germany, France, Canada, Russia, Israel and Japan. 

That adaptive trial will eventually enroll around 300 patients and study intravenous Kevzara as an add-on to supportive care, Regeneron said, but its design may change in light of the U.S. monitoring committee's recommendations. 

RELATED: Sanofi, Regeneron ready to roll Kevzara into COVID-19 trials immediately

Kevzara is one of a group of IL-6 inhibitors targeted for COVID-19 trials alongside Roche's Actemra and EUSA Pharma's Sylvant after anecdotal results in China showed early promise in treating the disease. 

The growing demand to evaluate meds repurposed to treat COVID-19 has been a boon for Roche, which posted 30% sales growth for Actemra in the first quarter to $687 million. Roche itself recently launched a randomized, placebo-controlled trial of Actemra in hospitalized patients, potentially angling to beat Sanofi and Regeneron to the punch.