Infectious disease specialists are protesting a huge overnight increase in the price of a 62-year-old drug used to treat a life-threatening parasitic infection.

The drug, Daraprim, was acquired last month by Turing Pharmaceuticals, a start-up run by a former hedge fund manager, which immediately raised the price to $750 a tablet from $13.50, The New York Times reported.

That brings the annual cost of treatment to hundreds of thousands of dollars.

“What is it that they are doing differently that has led to this dramatic increase?” said Judith Aberg, M.D., the chief of the division of infectious diseases at the Icahn School of Medicine at Mount Sinai. She said the price increase could force hospitals to use “alternative therapies that may not have the same efficacy.”

In recent months, critics have slammed pharmaceutical companies high prices on new drugs for diseases like cancer, hepatitis C, and high cholesterol, as well as older drugs, some of them generic.

Although some price increases have been caused by shortages, others have resulted from a business strategy of buying old neglected drugs and turning them into high-priced “specialty drugs,” The Times reports.

In August, Sen. Bernie Sanders, who is seeking the Democratic nomination for president, and Rep. Elijah E. Cummings, D-Maryland), wrote to Valeant Pharmaceuticals after that company acquired two heart drugs, Isuprel and Nitropress, from Marathon Pharmaceuticals and promptly raised their prices by 525 percent and 212 percent respectively. Doxycycline, an antibiotic, went from $20 a bottle in October 2013 to $1,849 by April 2014, according to the two lawmakers.

This week, Hillary Rodham Clinton also called for controlling the cost of prescription drugs, a key fix Obamacare.

"We have a lot of positives. But there are issues that need to be addressed," the Democratic presidential front-runner said Sunday on CBS' Face the Nation. "I'm going to address them this week, starting with how we're going to try to control the cost of skyrocketing prescription drugs. It's something I hear about everywhere I go."

The Infectious Diseases Society of America and the HIV Medicine Association sent a joint letter to Turing this month calling the price increase for Daraprim “unjustifiable for the medically vulnerable patient population” and “unsustainable for the healthcare system.” An organization representing the directors of state AIDS programs has also been looking into the price increase, according to doctors and patient advocates.

Martin Shkreli, chief executive of Turing, said that the drug is so rarely used that the impact on the health system would be minor and that Turing would use the money it earns to develop better treatments for toxoplasmosis, with fewer side effects.

“This isn’t the greedy drug company trying to gouge patients, it is us trying to stay in business,” Shkreli said. “This is still one of the smallest pharmaceutical products in the world. It really doesn’t make sense to get any criticism for this.”