Shares of Acorda Therapeutics are sinking after the company announced this morning that it has increased the frequency of blood cell count monitoring for participants to weekly in its Phase 3 program of tozadenant for Parkinson’s disease.

The company took this action in response to “cases of agranulocytosis, possibly drug-related, and in some cases associated with sepsis and death.” Acorda also paused new enrollment in the long-term safety studies, pending further discussion with the independent Data Safety Monitoring Board and the FDA. Including the previously conducted Phase 2b study, approximately 890 patients have been exposed to tozadenant and 234 have been exposed to placebo. “There have been seven cases of sepsis, all in the tozadenant groups, five of which were fatal,” the company said in a statement today. Four of the sepsis cases were associated with agranulocytosis, two had no white blood cell counts available at the time of the event and one had a high white blood cell count, it added. Shares of Acorda are down 37%, or $10.35, to $17.85 in early trading.