Overwhelmed by demand for an experimental treatment for coronavirus, the drug maker Gilead abruptly shut down its emergency access program, leaving doctors and families scrambling for answers.

The company said it was setting up a broader access program that could try to help more people, but some said the transition is delaying remedies for very ill patients who have few options.

“We have heard zero. We know nothing,” said Genny Allard, the mother of Jack Allard, a 25-year-old New Jersey resident who is in a medically induced coma and on a ventilator at Hackensack Meridian Health JFK Medical Center in Edison, N.J. “I’m just, like, apoplectic at this point. I have a kid who is sick and the doctor wants to give him the next medicine that is supposed to help.”

The drug, remdesivir, is being studied in several large-scale clinical trials around the world, including a huge trial announced last week by the World Health Organization. But the results have not been reported yet, and it is still unclear whether the drug works against the coronavirus. It was studied to treat Ebola, but did not work well enough against that virus.