Antibiotics have a special place in the world of medicine. Statins, anti-malarials and chemotherapy drugs may have a reputation for being life-saving, but none has had the lasting impact of antibiotics, which are estimated to have saved 200 million lives in the last 65 years.

But that success has led to problems. In the past three decades, antibiotics have been prescribed in ever-growing numbers — at an estimated cost of $2.8 billion a year — sometimes to treat viral ailments that aren’t helped by the drugs. Antibiotics also are found increasingly in animals farmed as food — 29 million pounds worth in 2009, according to the Food and Drug Administration — to kill bacteria and boost growth.

At the same time, some bacteria, including those found in hospitals and the community, are developing resistance to previously effective antibiotics. As a result, physicians have to prescribe larger doses to get the same result or, in some cases, switch to more powerful versions of the drugs, some of which have toxic side effects. Even more concerning is the presence of bacteria that are resistant to all drugs, leaving doctors with no options for formerly treatable infections.

It’s natural for bacteria to develop resistance to something that’s adept at killing them, but the explosive use of antibiotics is speeding up the biological process, leaving some physicians fearful that modern medicine may end up back in pre-penicillin days.

“Before we began using antibiotics, these resistance mechanics were already in nature, but in a very low rate,” said Dr. Brad Spellberg, an infectious disease specialist with the UCLA David Geffen School of Medicine. “Any use of antibiotics drives resistance, even appropriate use. But inappropriate use increases the rate faster.”

In an effort to prevent widespread resistance, physicians across the globe are promoting the judicious use of antibiotics and emphasizing the development of new drugs. Pediatricians and family practice doctors are backing off patient requests for antibiotics, with some instead offering a safety-net prescription to be filled only if symptoms don’t improve. Hospitals, which have seen some of the worst effects of antibiotic resistance, are adopting stewardship programs that aim to make sure drugs aren’t being overused.