The U.S. government’s supply of remdesivir, a medication used to treat COVID-19 patients that was donated by its manufacturer, will run out by the end of this month.

Dr. Robert Kadlec, an official in the Department of Health and Human Services, said that the government is working with Gilead Sciences, the company that developed the drug, to ramp up production, but it is uncertain when more will be available.

Remdesivir proved effective in clinical trials in treating severely ill patients with COVID-19. The patients experienced rapid recovery in both fever and respiratory symptoms.

According to STAT News remdesivir was one of the first medicines to be a considered a candidate to treat SARS-CoV-2, the virus that causes COVID-19. The U.S. Food and Drug Administration gave emergency authorization for the intravenous drug to be used in hospitalized COVID-19 patients last month.

According to  CNN, the government’s final shipment of remdesivir is scheduled to go out June 29, but it’s not clear when more of the drug will be available and what it will cost. Gilead originally donated 940,000 vials, and now that the free supply is waning, officials are concerned that the price for future medication will skyrocket.

“The price that Gilead can charge, as with any pharmaceutical company in America, appears to be the sky’s the limit — whatever sick and dying people will pay,” said Rep. Lloyd Doggett, a Texas Democrat who chairs the House Ways and Means Committee, according to CNN.

The government controls remdesivir distribution under the rules of its emergency authorization, according to CNN. Kadlec said no decisions have been made as to whether the government will continue its role, or allow the drug to be distributed through normal channels.

According to Fierce Pharma, Gilead CFO Andrew Dickinson said the per-patient cost would be $30,000 but that the company will charge a fraction of that amount.

Gilead is ramping up production to make more of the drug, but the projected availability is unclear, according to CNN. It was noted that the drug is not appropriate for all COVID-19 patients, and ultimately the doctors would be the ones to decide who gets treated.