Ebola has killed more than 1,000 people and sickened nearly 2,000 in the current West African outbreak that has also hit Guinea, Liberia and Nigeria. Many of the dead are health workers, who are often working with inadequate supplies and protection.
At the time that the experimental treatment was being considered for Dr. Sheik Humarr Khan, his immune system was already starting to produce antibodies suggesting he might recover, Doctors Without Borders said in the statement. Khan was also due to be transferred to a European hospital that would be more capable of handling problems that might arise, it said.
The experimental drug, ZMapp, is designed to boost the immune system to help it fight the virus. Since Khan's body was already producing an immune response, the doctors may have feared that any boost would kick it into overdrive.
In the end, the treating physicians decided against using the drug. They never told Khan of its existence because they felt it would be unethical to tell him of a treatment they might not use. Shortly after their decision, however, Khan's condition worsened, the statement said, and the company providing the medical evacuation decided not to transfer him. He died a few days later, on July 29.
"Every day, doctors have to make choices, sometimes difficult, about treatment for their patients," said the Doctors Without Borders statement. "Trying an untested drug on patients is a very difficult decision, particularly in the light of the 'do no harm' principle."
ZMapp has since been given to two U.S. aid workers and a Spanish missionary priest. The Americans are improving, although it is unclear what role ZMapp has played in that, but the priest died Tuesday.
The last known doses of ZMapp arrived in Liberia on Wednesday, carried personally by Foreign Minister Augustine Ngafuan. The California-based company that makes the drug, Mapp Pharmaceuticals, has said that its supplies are now exhausted, and it will take months to produce even a modest amount.
The drug has never before been tested in humans, and it is not clear if it is effective or even harmful.
Dr. Moses Massaquoi, who helped the Liberian government acquire it, told reporters at the airport that there was enough to treat three people. Previously, the government had said it would only have enough to treat two sick doctors.
They would be the first Africans known to receive the treatment.
While many have called for more experimental drugs to be made available, noting that Ebola patients often have little to lose and so much to potentially gain, others have expressed caution.
"To use this drug without having any information on its human benefits or dangers runs the risk of mistakenly thinking it is either effective or not based upon anecdotal evidence, a difficulty that could prove disastrous for later in this outbreak or future ones," said Dr. Philip M. Rosoff, director of the Clinical Ethics Program at Duke University Hospital.
The maker of another experimental Ebola drug said Wednesday that it is not ready to make the treatment available. Canada's Tekmira Pharmaceuticals Corp. said it is continuing talks with governments and international agencies.
The Canadian government has promised to donate 800 to 1,000 doses of its untested Ebola vaccine to the World Health Organization.
Shelly Glover, the Canadian regional minister for Manitoba, where Canada's National Microbiology Laboratory is located, said Wednesday that the vaccines haven't left Canada yet. She said WHO is assembling a panel of experts to help decide who will get one.
Likely candidates are health care workers in Africa who are among the most vulnerable because of their close contact with Ebola patients.
Massaquoi, from Liberia, said negotiations for access to the vaccine are taking place now. Guinea is also considering asking for it.
Unlike ZMapp, which is being given to only a handful of people and is unlikely to yield significant information about the drug's effectiveness, the vaccine could be tested in a small, but more rigorous field trial.
"It gives us an opportunity to test the vaccine in an outbreak situation in populations that are at risk," said David Heymann, who professor at London School of Hygiene and Tropical Medicine.
Meanwhile, Nigeria confirmed that another person has died from Ebola, bringing the toll in that country to three. The man was under quarantine because he had contact with Patrick Sawyer, a Liberian-American who flew into Nigeria with the disease and died of it last month.
Cheng reported from London. Associated Press writers Clarence Roy-Macaulay in Freetown, Sierra Leone, Jonathan Paye-Layleh and Wade Williams in Monrovia, Liberia, Boubacar Diallo in Conakry, Guinea, Maram Mazen in Lagos, Nigeria, Matt Perrone in Washington and Rob Gillies in Toronto also contributed.