First Big Pharma fled the field, and now start-ups are going belly up, threatening to stifle the development of new drugs.

At a time when germs are growing more resistant to common antibiotics, many companies that are developing new versions of the drugs are hemorrhaging money and going out of business, gravely undermining efforts to contain the spread of deadly, drug-resistant bacteria.

Antibiotic start-ups like Achaogen and Aradigm have gone belly up in recent months, pharmaceutical behemoths like Novartis and Allergan have abandoned the sector and many of the remaining American antibiotic companies are teetering toward insolvency. One of the biggest developers of antibiotics, Melinta Therapeutics, recently warned regulators it was running out of cash.

Experts say the grim financial outlook for the few companies still committed to antibiotic research is driving away investors and threatening to strangle the development of new lifesaving drugs at a time when they are urgently needed.

“This is a crisis that should alarm everyone,” said Dr. Helen Boucher, an infectious disease specialist at Tufts Medical Center and a member of the Presidential Advisory Council on Combating Antibiotic-Resistant Bacteria.

The problem is straightforward: The companies that have invested billions to develop the drugs have not found a way to make money selling them. Most antibiotics are prescribed for just days or weeks — unlike medicines for chronic conditions like diabetes or rheumatoid arthritis that have been blockbusters — and many hospitals have been unwilling to pay high prices for the new therapies. Political gridlock in Congress has thwarted legislative efforts to address the problem.

The challenges facing antibiotic makers come at time when many of the drugs designed to vanquish infections are becoming ineffective against bacteria and fungi, as overuse of the decades-old drugs has spurred them to develop defenses against the medicines.

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