Doctors mean well, but new data suggests that many physicians are following old protocols that are fueling dangerous antibiotic resistance.

Taking your doctor’s advice is usually the best medicine.

But patients who are prescribed high-powered antibiotics for sore throats should second-guess their doctor’s opinions because they won’t help in 90 percent of sore throat cases. And new data suggests the outdated practice continues to fuel a major threat to human health: antibiotic resistance.

A new study published in the journal JAMA Internal Medicine says that despite nearly 40 years of knowing better, many doctors still routinely prescribe expensive broad-spectrum antibiotics for sore throats.

While only about 10 percent of all sore throats are caused by group A streptococcal (GAS) bacteria, or strep for short, about 60 percent of sore throat cases are being treated with azithromycin, a powerful antibiotic that experts say should only be used for proven bacterial infections. Instead, researchers Dr. Michael L. Barnett and Dr. Jeffrey A. Linder say patients are better served by using tried-and-true penicillin.

Using data from 8,191 sampled sore throat cases out of 92 million estimated doctor’s office visits from 1997 to 2010, the researchers found penicillin was used in nine percent of the cases, while azithromycin was used in 15 percent of cases.

“Prescribing of penicillin, which is guideline-recommended, inexpensive, well-tolerated, and to which GAS is universally susceptible, remained infrequent,” the study authors wrote.

The prescription rates for antibiotic drugs have fallen from near 80 percent in 1993. Until the 1970s, doctors routinely gave patients antibiotics for the flu, the common cold, and other temporary conditions not caused by bacteria.

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“In conclusion, despite decades of effort, we found only incremental improvement in antibiotic prescribing for adults making a visit with sore throat,” the researchers stated.

Scientists involved in the latest study noted that their data did not include information about whether the prescriptions were appropriate for the condition, but did say that 90 percent of sore throats are not caused by bacteria.

The World Economic Forum has called antibiotic resistance “arguably the greatest risk” to human health, and the U.S. Centers for Disease Control says that reducing this resistance is its top priority.

Antibiotics become ineffective from overuse because bacteria evolve to outwit the drugs, creating new strains of bacteria that can outsmart the strongest antibiotics on the market.

Earlier this week, more than 300 people fell ill after eating chicken carrying a strain of salmonella that’s antibiotic-resistant.

And research published in The New England Journal of Medicine shows that in 2009 U.S. patients were given more than 6.5 million pounds of antibiotics, and in 2010 another 28.6 million pounds were given to livestock.

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Besides increasing the prevalence of antibiotic-resistant bacteria, the continuing practice of giving broad-spectrum antibiotics for sore throats cost the U.S. $500 million from 1997 to 2010, the researchers said.

Moreover, these antibiotics can cause short-term side effects, including diarrhea, stomach pain or upset, dizziness, and vaginal itching or discharge.