(CNN) It's the first and only drug shown to be effective against the novel coronavirus in a rigorous trial. Its effects are modest but significant -- shortening a patient's hospital stay by about four days. Dr. Anthony Fauci, the nation's top infectious disease specialist, has called it the new "standard of care" for Covid-19.
But as it stands now, there's only enough remdesivir in the world for about 200,000 patients, according to the drug's maker, Gilead Sciences. Who will those patients be?
The US government, which is deciding where remdesivir goes, has offered few answers and little guidance since the drug was authorized for use on hospitalized patients a week ago.
No comprehensive plan for distribution has been publicly released in the days since. But doctors and pharmacists on the front lines tell CNN that the process for accessing the drug has been opaque.
"Will we get it? Yes, no? What's the speed at which we're going to get it? Every day that you delay getting the drug to a particular hospital or a community means lives lost," said Dr. Peter Chin-Hong, a professor of medicine at the University of California, San Francisco School of Medicine.
As of now, there appears to be no way to apply for remdesivir, according to six doctors and pharmacists who spoke to CNN. Chin-Hong said one colleague described the process as: "Don't call us, we'll call you."
Asked about the plan on Sunday, the US Department of Health and Human Services told CNN to contact the Federal Emergency Management Agency, which said the drug would be distributed "based on an allocation plan approved by the White House Task Force."
But asked for an update on Wednesday, FEMA directed CNN back to HHS, saying that agency would be handling the drug's distribution. HHS and the White House task force, for their part, did not respond to CNN's requests for comment.
AmerisourceBergen, the distributor for remdesivir in the United States, offers a vague explanation on its website: "If you are a hospital identified by the U.S. government as a recipient for donated remdesivir, you will be proactively contacted by an AmerisourceBergen representative."
That donation refers to 1.5 million vials of remdesivir that Daniel O'Day, Gilead's CEO, has said the company is providing to the US government to allocate -- enough for between 100,000 and 200,000 treatment courses.
But O'Day has also said the company plans to distribute that donation globally. Asked for clarification last weekend, Gilead spokesperson Sonia Choi told CNN: "We are working with regulatory authorities worldwide and bioethicists to help inform our global allocation approach."
"If you had to boil it down, the one thing that I'm concerned about is just lack of transparency," said Chin-Hong.
He said he has discussed remdesivir access with doctors around the country, "and I think the pervasive feeling that I would say everyone in this group has is anxiety. And that's because of lack of transparency."
Doctors understand that there is a limited supply of the drug and that resources need to be rationed, Chin-Hong said. "But there's no process, there's no way to go and look something up when you want to advocate for your own hospital or advocate for your own community."
CNN medical analyst Arthur Caplan, founding head of the Division of Medical Ethics at the New York University School of Medicine, has studied these issues before. "One thing we know about rationing is people will accept it if they understand the rationale," he said.
"But when you ration and you don't explain what you're doing, when you're not transparent, when you don't make any effort to explain who's getting something and who isn't -- particularly in a time when panic is everywhere with respect to trying to treat people who are ill with [Covid-19] -- then you're going to breed a huge backlash, which is what you're seeing."
The frustration from doctors is one thing, Caplan said, but anger from patients and their families is likely to come too if they aren't able to access the drug -- and don't understand why.
"This morning I wake up to realize that drug was promised to a handful of hospitals with no obvious criteria," said Dr. Nicole Theodoropoulos, an associate professor at the University of Massachusetts Medical School, on Thursday. "It's difficult to know what to tell patients when there is no transparency about the process."
Gilead Sciences has not responded to CNN's request for comment, although the company has said that "tens of thousands" of courses of remdesivir would begin shipping out this week. The company has set a goal of producing more than a million courses by December.
In a statement, AmerisourceBergen, the drug's distributor, said: "Decisions on which hospitals and the quantity of the product they will receive are being made by the government with AmerisourceBergen using our infrastructure and expertise to efficiently move any product we receive from Gilead in keeping with the government's directives."
The FDA-authorized drug is infused through an IV, and its use is limited to hospitalized patients with severe disease. But Daniel O'Day, chairman and CEO of Gilead Sciences, has said Gilead is looking at other formulations of remdesivir too -- including an inhaled version that could be given outside of the hospital.
"I think people are frustrated," said Dr. Michael Ison, a professor of infectious diseases at the Northwestern University Feinberg School of Medicine.
"We've got patients that are sick and dying from Covid-19. We want to give them the best possible therapy and we don't have access to it. We don't know how to get access to it. No one knows how to advocate for your hospital to have this drug made available to your patients."
He described the delicate balancing act that doctors have to navigate: "If we know we're going to get [remdesivir] for patients, we may hold off on giving other therapies because we know we're going to be getting this therapy that we can offer them instead."
The frustration, he said, is that "we have no idea what the process has been to be selected." The only way to get a glimpse into where the drug is going, he said, is through an ad hoc website put together by researchers at UCSF.
"I've collated an unofficial list of hospitals who are and are not currently slated to receive the drug through a survey of pharmacists and physicians," said Conan MacDougall, a professor of clinical pharmacy at the UCSF School of Pharmacy.
Some major medical centers may be able to provide remdesivir to patients under existing research programs, MacDougall said, but not all patients are eligible for those.
Clinical trials and so-called expanded access programs, which have long been available, can have stringent criteria. And when the US Food and Drug Administration issued an emergency use authorization for remdesivir last week, it framed the move as a way to increase access to the drug.
The FDA issued a similar emergency authorization during the H1N1 pandemic for another antiviral medicine, peramivir. But back then, the US Centers for Disease Control and Prevention was responsible for managing the drug's distribution. As described in The New England Journal of Medicine in 2009, the CDC created an online portal for physicians to request the drug at a time when just 1,200 treatment courses were available.
Like others CNN spoke to, Dr. Cameron Wolfe, an associate professor of medicine at the Duke University School of Medicine, said he understands that limited supplies need to be distributed across the country.
"It's one thing to say, well, we just don't have enough, and it's going to cities that are being heavily hit. I think most families would understand that. It's a hard call, but I think they would understand why."
With no idea of how drugs are being rationed, though, "I can't even say that. I can't even look my colleague in the face and say I know why we are not getting access to this drug.
"That makes for difficult conversations. That makes for painful conversations. And it just doesn't allow you to plan from a hospital point of view."
On Wednesday, the Infectious Diseases Society of America and the HIV Medicine Association wrote a joint letter to Vice President Mike Pence, urging the federal government to ensure the "fair and equitable distribution of remdesivir."
The plan for allocating the drug, they said, should be based on evidence about the virus' spread. "Data on the distribution of remdesivir under the [emergency uses authorization] should be publicly available," they added.