Both Ebola patients being brought to Atlanta for treatment received an experimental drug before leaving Africa, CNN reported Monday.

At least in the case of Dr. Kent Brantly, the untested drug had an immediate positive result, the network reported. The second patient, missionary Nancy Writebol, also showed improvement after receiving two doses.

Brantly arrived at Emory University Hospital over the weekend and is being cared for in a special isolation unit. Writebol is scheduled to arrive Tuesday.

The drug that they were given, called ZMapp, was developed by Mapp Biopharmaceutical Inc., which is based in San Diego, CNN reported. It is produced by exposing mice to fragments of the Ebola virus and then harvesting antibodies from their blood.

Up to now, there has been no known treatment for Ebola, which can kill upwards of 80 percent of its victims, depending on the strain.

It is not known how soon ZMapp could be in commercial production. That process is typically a long one, but the it can be hastened in urgent cases where the Federal Drug Administration grants permission for “compassionate use.”

Mapp Biopharmaceutical did not immediately return phone calls seeking comment Monday.

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