Investing.com -- Sanofi (EPA:SASY) shares fell more than 9% on Thursday after the drugmaker reported results from a large trial of its experimental eczema treatment amlitelimab that showed weaker effectiveness than expected, though safety results were strong.
The Phase III trial, called COAST 1, tested amlitelimab in people with atopic dermatitis, a chronic skin condition marked by itching and inflammation.
Patients received the treatment either every four weeks or every 12 weeks over a 24-week period.
One main measure of success was the percentage of patients reaching what is known as EASI-75, a standard score for eczema severity.
Results showed 16.8% improvement in the every-four-week group and 20% in the every-12-week group compared with placebo.
Those numbers were below what was seen in an earlier, smaller study of the drug and at the lower end compared with other medicines used to treat the condition.
A second measure, known as vIGA-AD, also came in modest. About 16% of patients on the four-week schedule and 18.6% on the 12-week schedule reached clear or almost clear skin, compared with placebo.
Company charts suggested the drug's effect continued to improve between weeks 16 and 24 of treatment.
Placebo responses, patients who improved without receiving the drug, were higher than those seen in past trials of Dupixent, Sanofi's blockbuster eczema treatment.
Analysts noted that the characteristics of patients in the amlitelimab study, including how many had already tried other advanced therapies, will be important to understanding the results.
Sanofi underscored amlitelimab's safety record in the trial. The most common side effects were conditions such as colds and upper respiratory infections, which appeared more often in the placebo group than among patients given amlitelimab.
Mild injection site reactions were slightly more common in the amlitelimab group at 2.2% versus 0.7% for placebo, but none were serious or caused people to stop treatment.
"Whilst placebo-adjusted efficacy may initially disappoint, management emphasises the clean safety profile," Jefferies analysts said in a note.
They added that the drug "may be positioned as an attractive maintenance drug" after patients first start on more potent treatments.
The results also contrasted with Amgen's experimental eczema drug rocatinlimab, which works differently. Amgen's treatment has been linked to higher rates of fever and chills.
In the amlitelimab trial, only 1.1% of patients reported fevers and 0.4% reported chills, numbers similar to placebo. By comparison, Amgen’s Phase III trial recorded 9% of patients with fever and 5% with chills.