A North Carolina drugmaker plans to test its experimental antiviral drug in patients who have Ebola, after getting authorization from regulators at the Food and Drug Administration.

Chimerix Inc. said Thursday that it has received FDA clearance to proceed with a trial examining the safety and effectiveness of its brincidofovir tablets in patients who have the virus. The company said in a statement that the drug is available for immediate use in testing.

With the FDA's permission, the Durham, North Carolina, drugmaker previously made the drug available to the first Ebola patient diagnosed in the U.S., who died in Dallas last week. Chimerix did not immediately return requests for comment.

The FDA does not publicly confirm when it has granted companies permission to begin testing. The agency has not approved any drugs as safe and effective in treating Ebola.

Brincidofovir is an antiviral drug being developed to treat several types of viruses, including one that infects patients undergoing bone marrow transplants. Chimerix is working with the U.S. Department of Defense on developing the drug as a treatment against smallpox. Laboratory tests suggested it may also work against Ebola.

Chimerix's drug is one of three experimental medications known to have been used on Ebola patients during the current outbreak. The other two are:

- ZMapp from San Diego-based Mapp Pharmaceuticals, which was developed specifically as an Ebola treatment. It is a cocktail of antibodies engineered to recognize the virus and bind to infected cells. Supplies are exhausted, though federal officials say work is underway to produce more.

- The TKM-Ebola injection, by Tekmira Pharmaceuticals of Canada, works by blocking genes that help the Ebola virus reproduce and spread. It has been used in at least one patient and is said to be in limited supply.