A critical drug which treats childhood cancers is in dwindling supply in the United States — a situation doctors are describing as a “nightmare.”

The drug, Vincristine, is used to treat common childhood cancers such as leukemia and lymphoma, but has become increasingly scarce after one of two manufacturers stopped making it in July.

On Friday, the FDA announced supplies would be fully recovered by January 2020, but the medication is now on back-order and doctors throughout the country are facing the difficult decision of rationing the drug to their young and sick patients.

There is no alternative to Vincristine.

“This is truly a nightmare situation,” Dr. Yoram Unguru, a pediatric oncologist at the Herman and Walter Samuelson Children’s Hospital at Sinai in Baltimore told The New York Times, who first reported on the shortage last week.

“Vincristine is our water. It’s our bread and butter. I can’t think of a disease in childhood cancer that doesn’t use vincristine.”

Almost 16,000 children are diagnosed with cancer in the US each year, according to the American Childhood Cancer Organization.

Dr. Michael Isakoff at Connecticut Children’s Medical Center in Hartford said his team treats up to 100 children diagnosed with cancer each year.

“We completely rely on Vincristine,” Isakoff told NBC Connecticut. “Our patients rely on it. It’s a critical drug to the treatment of children with cancer.”

Earlier this year Teva, one of two manufacturers of the drug, made a “business decision” to discontinue it, according to the FDA — leaving Pfizer as the sole supplier of Vincristine in the US.

Manufacturing problems have led to a delay at Pfizer, the FDA said.

A Pfizer spokeswoman last week said they would expedite shipping in the coming weeks and ramp up production to four times what they typically made before Teva withdrew from the market.

Children’s Oncology Group chair Peter C. Adamson said he was “infuriated” by the “greatly concerning” shortage.

“We find the situation forced upon pediatric oncologists and families of children with cancer unacceptable,” he said in a statement.

“I am hopeful we can take this unacceptable crisis and move towards better answers, always keeping the interests of patients and families central to our efforts.”