We're finding out more and more about the risks of a common medicine once considered a wonder drug

When Alexander Fleming discovered penicillin in 1928, it was hailed as a wonder drug. For the first time in history, bacterial infections that were once a death sentence could now be treated with a few pills.

But almost as soon as antibiotics were discovered, scientists began to realize their limitations. Bacteria quickly became resistant to the drugs, spawning "superbugs" that were immune to most treatments.

And scientists are now finding out that even when they're effective, antibiotics can have serious, and sometimes permanent, side effects.

An FDA advisory panel is calling for better warning labels on a group of frequently prescribed antibiotics called fluoroquinolones, The Wall Street Journal reported.

Common drugs, toxic effects

Most fluoroquinolones are sold as generic drugs, but they also include well-known drugs such as Bayer AG's Cipro, (generic name ciprofloxacin) and Johnson & Johnson's Levaquin (levofloxacin). They are prescribed to treat everything from bronchitis to sinus infections and urinary-tract infections (UTIs), and more than 36 million prescriptions were written for these drugs in 2014, The Journal reported.

But there's been mounting evidence over the last few years that these drugs may cause side effects, ranging from heart problems to peripheral nerve disorders and even trouble concentrating.

Many newer fluoroquinolones are no longer prescribed because of their toxic effects, according to the medical book Merck Manual. For example, companies stopped making a drug called trovafloxacin because it was found to cause severe liver problems, and gatifloxacin because it could cause dangerously low or high blood sugar.

Patients and doctors testified before an advisory panel to the FDA on Thursday about the risks and benefits of these drugs.

One woman who testified said she had been healthy when she took Levaquin in March 2014 to treat non-life-threatening pneumonia. But after taking the drug, "all my tendons were damaged," she told the panel, according to The Journal. "Nine pills took my health away. I suffered excruciating pain over a year," she said, adding that she now walks with crutches.

Several doctors who represent drug companies were also present at the hearing and testified to the benefits of the antibiotics in question. For example, they said fluoroquinolones are important for treating cases of bronchitis in people with chronic obstructive pulmonary disease or COPD, which can be fatal if untreated.

The FDA panel was asked to evaluate drug labels for how well they describe the risks and benefits of several uses. They voted unanimously to revise the labels on antibiotics prescribed to treat sinusitis, 18-2 (with one abstention) for bronchitis, and 20-1 for urinary-tract infections, The Journal reported.