WASHINGTON — Martin Shkreli, a former pharmaceutical executive serving a seven-year prison sentence for defrauding investors, was accused on Monday of trying to maintain a monopoly over the lifesaving drug Daraprim through anticompetitive tactics.

The Federal Trade Commission and the office of the New York attorney general, Letitia James, jointly sued Vyera Pharmaceuticals and the company’s owners, Mr. Shkreli and Kevin Mulleady, in a federal court in Manhattan. They say Vyera and its leaders had an “elaborate and anticompetitive scheme” that blocked generics from entering the market after the company jacked up prices of Daraprim. The drug is used to treat toxoplasmosis, a rare, potentially fatal parasitic infection.

Mr. Shkreli became known as a “pharma bro” for his brash attitude when faced with criticisms for raising prices of Daraprim by 5,000 percent, making it prohibitively expensive. In 2018, he was sentenced to prison for defrauding investors in hedge funds he ran by lying about his performance and track record.

In their suit, the F.T.C. and New York attorney general say that soon after Vyera bought the rights to Daraprim in August 2015, it raised the price per tablet to $750 from less than $20, knowing the increase would attract generic competition. Before Vyera’s purchase of Daraprim, the drug had been accessible and affordable for decades. Daraprim is the only drug approved by the Federal Drug Administration to fight toxoplasmosis, which can kill people who have compromised immune systems, including babies and H.I.V. patients.