Chimerix reported today that a Phase 3 trial for its antiviral medication brincidofovir failed to meet the required benchmark goals. As a result, shares of the company’s stock plunged in early trading, falling by as much as 79.43% to $7.32 per share. Chimerix closed out trading on the last trading day (Dec. 24) above $35 per share.

Chimerix, Inc. (CMRX)Tanks After Report Of Failed Late State Trial

Volume was also extremely heavy today. As of 9:41 a.m., already 2.12 million Chimerix shares had changed hands. The average daily volume is 307,491 shares.

Mixed results on Chimerix’s lead drug

Brincidofovir was in testing for treatment of patients undergoing stem cell transplants. The late stage trial found that patients who were taking the drug didn’t see a significant reduction in infections of cytomegalovirus, which is a virus that belongs to the herpes family. The drug is also Chimerix’s lead drug, and its failure in the late stage signals serious trouble for the pharmaceutical firm.

During the testing period, through the 14th week after the participating patients received their hematopoietic cell transplantation, fewer of those taking brincidofovir were infected with cytomegalovirus compared to the control group. However, between the 14th and 24th week, testers found an increase in infections with the virus in patients taking the drug compared to those who were not taking it. Researchers also noted a very slight increase in mortality among patients who were taking the drug when compared to those who were not, although this increase was not statistically significant.

Graft-versus-host disease presents a problem

Chimerix said today that based on preliminary analysis of the results, the probable reason brincidofovir did not achieve its main goal was because of a complication called graft-versus-host-disease, which happens when the stem cells that are being transplanted attack the patient’s body. Graft-versus-host-disease causes a much higher rate of corticosteroids being prescribed compared to the control group. Both GVHD and corticosteroid use are risk factors for cytomegalovirus infection occurring late in the treatment period after receiving the stem cell transplant and discontinuing use of the antiviral drug.

“The population of allogeneic stem cell transplant recipients is heterogeneous and complex,” said Chimerix Chief Medical Officer W. Garrett Nichols, M.D. in a statement. “We will be evaluating the sub-groups of patients within SUPPRESS, such as T-cell depleted transplant recipients who have a lower risk of GVHD, to better understand these results and inform our next steps. We are reaching out to investigators and other experts to help us assess the complete data set to understand what may have caused the results of the SUPPRESS trial to differ substantially from those seen in the Phase 2 study.”

The drug was being tested in patients who had kidney transplants, and Chimerix has halted enrollments in the trail until the complete data from the study is available. However, it will continue testing brincidofovir in patients suffering from serious adenovirus infections and smallpox. The pharmaceutical company expects to release the full analysis of the trial at the BMT Tandem Meetings in February.