NEW YORK — U.S. doctors are prescribing enough antibiotics to give them to four out of five Americans every year, an alarming pace that suggests they are being overused, a new government study finds.

Overuse is one reason antibiotics are losing their punch, making infections harder to treat. The recent report gives the first detailed look at usage of these medicines in every state and finds it highest in the South and Appalachia.

“It sounds high,” said Keith Rodvold, a professor of pharmacy practice at the University of Illinois at Chicago.

There is no scientific consensus on an appropriate level of antibiotic prescribing. But some experts said the new study’s results are disturbing, and that rates are probably excessive even in the states with the lowest antibiotic prescription levels.

Antibiotics have been commonly available since the 1940s, and have done wonders at saving patients with infections ranging from pneumonia to sexually spread diseases. But bacteria have increasingly gained the power to shrug off antibiotics.

Experts say chances of resistance increase when antibiotics are not used long enough or are taken for the wrong reasons, allowing bacteria to survive and adapt. The Centers for Disease Control and Prevention is tracking at least 20 strains of resistant bacteria.

CDC researchers conducted the new study, analyzing a national prescription drug database for 2010. The findings are being published in the New England Journal of Medicine.

Other studies have focused on antibiotic prescriptions for specific groups like Medicare patients. This is the first to look at it for all Americans.

Doctors and other health care providers prescribed 258 million courses of antibiotics in 2010, for a population just shy of 309 million, the researchers found. That translates to 833 antibiotic prescriptions for every 1,000 people, on average.