The Japanese company behind an experimental Ebola treatment says it offers new hope for thousands of people infected with the deadly virus in west Africa, but acknowledged it is "not a miracle drug".
In their first comments to media since the release of early clinical trials last week, executives from Fujifilm's drug unit Toyama Chemical said the results were a "good first step" that could lead to larger and better-designed trials.
Avigan - approved for use in Japan as an influenza treatment - was somewhat effective at saving the lives of Ebola patients if given early in the illness, but not later, according to the results presented to a US conference.
"They were better than my expectations," Fujifilm director Yuzo Toda said in an interview at the company's office in Tokyo.
"Taking this medicine as early as possible (means) the mortality rate can be significantly reduced. That sends a very strong message to the patient."
Testing began late last year, led by INSERM, the French Institute of Health and Medical Research, and is being funded by the European Commission.
The ongoing clinical trial in hard-hit Guinea - dubbed Jiki, meaning hope in the local language - is testing the drug on patients with Ebola, which causes severe vomiting, diarrhoea and sometimes fatal bleeding.
Results from only 80 people are available so far, but they show that among those who received the drug early in their illness, 15 per cent died.
However, among those who received it when their viral load was high, 93 per cent died, according to the preliminary results presented at the Conference on Retroviruses and Opportunistic Infections in Seattle, Washington.
No help for most vulnerable
The death rate from the virus in the latest outbreak has ranged from 53 to 60 percent, according to the World Health Organization.
NGO Medecins Sans Frontieres (Doctors Without Borders), which is among those helping to carry out the trial, said it was happy to see the drug "seems to have a positive effect for certain patients".
"But it also seems that the most vulnerable patients, the people that are most likely to die from the disease, don't benefit at all," said the group's medical director Bertrand Draguez.
Toda and his colleagues acknowledged the drug's apparent limitations, but said any positive results could help spread the word among the worst-hit communities and convince more patients to sign up for clinical trials.
They hope the WHO will accelerate the use of Avigan to deal with the Ebola crisis.
"We didn't expect it would work for all patients, or be a miracle drug, but this is a very good first step," said Hiroshi Kitaguchi, general manager of the business development unit at Toyama Chemical, which developed Avigan.
"The results may not be a miracle, but we can say it is a miracle that we have (come) this far in such a short period of time."
Best known for its photo film and camera business, Fujifilm started to acquire healthcare firms nearly a decade ago in a bid to branch into other sectors as demand for camera film plummeted. Among them was Toyama Chemical, which it bought in 2008.