Dive Brief:An emerging class of drugs under development to treat multiple sclerosis suffered another blow Tuesday when Merck KGaA announced a Phase 3 failure for its entrant.In the so-called Evolution studies, the German drugmaker compared its evobrutinib drug with an approved treatment called teriflunomide, sold by Sanofi under the brand name Aubagioand also available generically. Researchers hoped to find an overall reduction in relapse rates for patients with the relapsing-remitting form of the disease.Instead, the study revealed little difference between the two treatment arms, with Aubagio surprisingly performing much better than in previous Phase 3 studies. Shares of Merck KGaA dropped8% in trading Wednesday in Germany.Dive Insight:The announcement is more bad news for a class of drugs known as BTK inhibitors. Just last week, Roches Genentech unit said the Food and Drug Administration placed a partial clinical hold on its program to develop a competing treatment called fenebrutinib on concern about potential liver damage.Merck KGaA faced a similar issue for evobrutinib back in April. And safety questions have also dogged tolebrutinib, under development by Sanofi.Now, though, the question is whether the drugs can effectively treat MS. Researchers found that the annualized relapse rate for Merck KGaAs evobrutinib was 0.11 in one trial and 0.15 in the other. By comparison, the rate was 0.11 and 0.14 for Aubagio, much lower than the 0.32 seen in the Tower trial of Aubagio.Its possible that current MS studies are enrolling less sick patients, skewing the results, Jefferies analyst Brian Balchin wrote in a note to clients. If so, that would have ramifications for the newer drugs being developed by Sanofi, Roche and Novartis, he said. He expects data from Sanofi in mid-2024, Roche in 2025 and Novartis in 2026.Merck KGaA said its undertaking a full evaluation of the data from the two Evolution trials and will present the results to the scientific community in the future. The safety profile in the study was consistent with the Phase 2 trial, the company said.BTK inhibitors target a protein called Brutons tyrosine kinase that is known to play a role in the proliferation of cancer cells and may also be involved in autoimmune disease. The FDA has already cleared a number of BTK inhibitors to treat cancer. Newer members of the class are designed to cross the blood-brain barrier, which is essential for a neurological disease like MS. '