An inhaled insulin championed by a billionaire medical entrepreneur appears headed for market failure after being abandoned by the company with the rights to market it.

MannKind, the developer of the insulin, announced Tuesday that Sanofi, the big French drug company with the marketing rights, was terminating the agreement between the two companies.

The move by Sanofi is not a surprise since the inhaled insulin, called Afrezza, has had dismal sales since being approved by the Food and Drug Administration in June 2014. Sanofi reported sales of only 5 million euros, or a little more than $5 million, in the first nine months of 2015.

Still, MannKind’s shares plummeted in trading Tuesday. The company is expected to face significant money problems without Sanofi’s support.

MannKind was started by Alfred E. Mann, who made a fortune founding aerospace and medical device companies, including the insulin pump manufacturer MiniMed, which was sold to Medtronic for about $3 billion. But Mann, now 90, spent much of his accumulated wealth backing MannKind as it suffered many setbacks before finally winning FDA approval of Afrezza.

Mann and other supporters of Afrezza said the product would provide millions of diabetics with a new option that might be more attractive to them than injecting themselves with insulin up to several times a day. But Pfizer had already suffered a costly failure in trying to market an inhaled insulin called Exubera.

MannKind had hoped to succeed where Pfizer failed because its inhaler was much smaller and more discreet — the size of a referee’s whistle, while Pfizer’s was the size of a tennis ball can. MannKind had also said its insulin had some desirable medical characteristics, other than being inhalable, although there was debate on that.

But Afrezza still faced obstacles, including concerns over the safety of putting insulin into the lungs. The prescribing information for Afrezza calls for lung function to be tested before patients start on the drug and periodically thereafter. The label also has a boxed warning, the strongest kind, that Afrezza should not be used by people with asthma or other chronic lung diseases because of the risk of bronchospasms. It is also not recommended for smokers or recent smokers.

Sanofi had hoped that Afrezza, which is taken at mealtimes, would be an adjunct to its big diabetes drug Lantus, which is a basal insulin taken once a day. Sanofi paid $150 million in 2014 to MannKind for the Afrezza rights in 2014 and another $50 million early in 2015.

But Sanofi wasted no time in jettisoning the product, acting almost immediately after Jan. 1, the first day it was allowed to give MannKind notice of termination.

Sanofi’s entire diabetes business, one of its major assets, is suffering now from price and product competition. That contributed to the ouster of its chief executive, Christopher Viehbacher, in October 2014. The new chief executive, Olivier Brandicourt, said in the fall that Sanofi’s diabetes business was expected to decline 4 to 8 percent annually from 2015 to 2018.

MannKind, based in Valencia, Calif., said in a news release Tuesday that the companies would try to effect a smooth transition of the marketing rights from Sanofi to MannKind, to be completed in no later than six months. It said it was reviewing its strategic options for Afrezza. But MannKind, a small company, is expected to face challenges in marketing Afrezza by itself, or in finding a new partner.

MannKind “now faces a difficult challenge of creating value for the product in a wholly owned and highly competitive environment,’’ Joshua Schimmer, an analyst at Piper Jaffray, wrote in a note Tuesday.

“At this point, we are skeptical that MNKD can find a new commercial partner for Afrezza given the stark failure of SNY’s efforts, even if they were halfhearted,’’ he wrote, using the stock symbols for MannKind and Sanofi.

A big challenge for MannKind could be raising money. It had only $32.9 million in cash and a debt of $185.4 million as of Sept. 30, according to a regulatory filing.

MannKind had a net loss of $91.4 million in the first nine months of 2015, even with Sanofi footing much of the bill to market Afrezza. As of Sept. 30, MannKind had an accumulated deficit of $2.6 billion since its founding.

At the time Afrezza was approved, Mann had provided about $1 billion to the company in equity and loans. He owned 37.8 percent of the stock as of March.

Hakan S. Edstrom, the chief executive of MannKind, resigned in November and was replaced on an interim basis by Mann, who had been the chief executive for many years. The new chief executive, who officially took office Tuesday, is Duane M. DeSisto, a former chief executive of Insulet, a manufacturer of insulin pumps.