These commonly prescribed drugs may have lethal effects

By John Murphy, MDLinx
Published April 23, 2019

Key Takeaways

Physicians are familiar with the common adverse effects of antibiotics, such as rash, diarrhea, and nausea. But they may not recognize the less common and potentially lethal complications associated with these very frequently prescribed drugs.

And antibiotics are indeed frequently prescribed. Each year, US providers write more than 270 million antibiotic prescriptions. That equates to more than four antibiotic prescriptions for every five Americans. Yet, about 30% of outpatient-prescribed antibiotics are not necessary. Keep this in mind as you review these lesser known adverse effects of antibiotics.


Hospital admissions for anaphylaxis are on the rise. In the United States and other countries, the most common cause of fatal anaphylaxis is medication, with antibiotics at the top of the list. Penicillins are the antibiotic class most frequently associated with fatal anaphylaxis, followed by cephalosporins, sulfonamides, and macrolides.


Antibiotics are an underrecognized cause of encephalopathy, according to the authors of a review of nearly 400 such cases in Neurology. These authors found that, among the different classes of antibiotics, encephalopathy was most commonly associated with penicillins, cephalosporins, antimycobacterials, quinolones, and macrolides. Seizures accompanying encephalopathy were most frequently associated with penicillin and cephalosporins.

The researchers also found that psychosis occurred in nearly half of all cases of antibiotic-associated encephalopathy, most commonly with sulfonamides, quinolones, macrolides, and penicillin procaine.

Hearing loss and disequilibrium

Antibiotics—notably the aminoglycosides—can be toxic to the ear, resulting in loss of hearing or equilibrium. Amikacin and kanamycin are toxic primarily to the cochlea (affecting hearing), while gentamicin, tobramycin, and streptomycin are preferentially vestibulotoxic (affecting equilibrium). Unlike common side effects that usually go away when the antibiotic is stopped, ototoxicity is frequently permanent. And the risk increases the longer the patient takes the drug. So, experts advise that when prescribing an aminoglycoside, consider keeping the duration of therapy to a minimum.


Certain antibiotics interact with sulfonylureas to increase the risk for hypoglycemia in people with diabetes. In one study of older patients with diabetes who were taking sulfonylureas, researchers reported that five antibiotics were associated with higher rates of hypoglycemia compared with other non-interacting antibiotics. In this study, an estimated 13.2% of all hypoglycemic events in patients prescribed sulfonylureas were associated with clarithromycin (odds ratio [OR]: 3.96), levofloxacin (OR: 2.60), sulfamethoxazole-trimethoprim (OR: 2.56), metronidazole (OR: 2.11), and ciprofloxacin (OR: 1.62).


As far back as 2008, the FDA mandated a “black box” warning on fluoroquinolones due to their increased risk for tendinitis and tendon rupture. Indeed, fluoroquinolones have been associated with arthropathy or tendinitis—especially Achilles tendon rupture—at a rate of 1%.

“While these drugs are effective in treating serious bacterial infections, an FDA safety review found that both oral and injectable fluoroquinolones are associated with disabling side effects involving tendons, muscles, joints, nerves, and the central nervous system. These side effects can occur hours to weeks after exposure to fluoroquinolones and may potentially be permanent,” the agency posted in 2016. The FDA added that these antibiotics should not be used for uncomplicated infections unless no other treatment options are available.

Aortic events

Another reason to proceed with caution when prescribing fluoroquinolones: They’ve been associated with an increased risk for aortic dissections and aneurysms.

In late 2018, the FDA issued a warning that fluoroquinolones can increase the risk of these rare but serious aortic events, which can lead to dangerous bleeding or even death. 

“Healthcare professionals should avoid prescribing fluoroquinolone antibiotics to patients who have an aortic aneurysm or are at risk for an aortic aneurysm, such as patients with peripheral atherosclerotic vascular diseases, hypertension, certain genetic conditions such as Marfan syndrome and Ehlers-Danlos syndrome, and elderly patients,” the FDA stated. “Prescribe fluoroquinolones to these patients only when no other treatment options are available.”

Why fluoroquinolones are associated with these increased risks to the aorta remains unknown.

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