Acadia Pharmaceuticals Inc., the San Diego-based company that developed the first-ever drug approved to treat hallucinations and delusions caused by Parkinson’s disease, saw its stock drop 23 percent April 9 after a news report about the deaths of some patients who were taking the drug.

As of market close the company’s market cap was down more than half a billion dollars, ending the day at about $2.06 billion from $2.68 billion on April 6.

Federal regulators greenlit the Acadia drug, called Nuplazid, in mid-2016. The drug was heralded for its potential because, unlike traditional antipsychotic drugs, it doesn’t function by suppressing dopamine production. Symptoms caused by Parkinson’s occur because of a deficiency of dopamine, making drugs that further reduce the level of the chemical in the brain inappropriate for such patients.

The report, published by CNN, drew attention to a November publication from the Institute for Safe Medication Practices, which analyzes U.S. Food and Drug Administration reports on “adverse events” related to prescription drugs. The publication noted reports of more than 200 deaths of patients who had been using the drug through March 2017.

The FDA uses such reports, which are submitted by consumers and health care professionals, to track potential issues with drugs.

Nuplazid, which was designated a “breakthrough therapy” by the FDA because of its potential compared to existing treatments, underwent an expedited review to speed its entry to market.

CNN reported that while a reviewing panel approved the drug 12-2, some members of the committee who voted in favor of it expressed concern about the limited testing the drug had undergone at the time.

In 2016 and 2017 combined, the FDA received 5,735 reports of “adverse events” ascribed to Nuplazid’s use from consumers and heath care professionals. Of those, 1,860 were termed “serious” cases, including deaths; 712 were reports of death, according to agency data. In that same time period, sales of Nuplazid topped $142 million.

In a statement, Acadia noted that psychosis related to Parkinson’s is typically seen in advanced stages of the disease, so those who would be candidates for its use typically have an overall high risk of death. It also emphasized the lack of a definite causal relationship between adverse events reported to the FDA and a particular drug or drugs a patient was using: “… (O)ne cannot calculate incidence of the event on that basis and the (FDA) data by themselves are not an indicator of the safety profile of the drug or biologic.”

Reach reporter Sarah de Crescenzo at sarahd@sdbj.com.