Fluoroquinolones and Delirium in Older Adults: What You Need to Know

When an older adult suddenly becomes confused, sees things that aren’t there, or can’t remember where they are, it’s easy to assume it’s dementia or just aging. But sometimes, the cause is something simpler-and more dangerous-than anyone realizes: a common antibiotic. Fluoroquinolones, including drugs like levofloxacin and ciprofloxacin, are widely prescribed for urinary tract infections, pneumonia, and other bacterial illnesses. Yet for people over 65, these antibiotics can trigger sudden, severe cognitive disturbances known as delirium. And unlike dementia, this confusion isn’t permanent-but it can be deadly if missed.

What Are Fluoroquinolones, and Why Are They So Common?

Fluoroquinolones are a class of antibiotics developed in the 1960s. They work by shutting down bacterial DNA replication, making them powerful against many types of infections. Because they’re effective and often taken as a single daily pill, doctors have relied on them for decades. In the U.S., about 7.8% of all outpatient antibiotic prescriptions are for fluoroquinolones. That’s millions of doses every year.

Common brands include Levaquin (levofloxacin), Cipro (ciprofloxacin), and Avelox (moxifloxacin). They’re used for everything from sinus infections to kidney infections. But their broad use doesn’t mean they’re safe for everyone-especially older adults.

How Fluoroquinolones Trigger Delirium

Delirium isn’t just forgetfulness. It’s a sudden, dramatic shift in mental state. Symptoms include:

• Confusion about time, place, or who people are
• Seeing or hearing things that aren’t real (hallucinations)
• Severe trouble focusing or following conversations
• Agitation, irritability, or extreme drowsiness
• Memory gaps that come and go throughout the day

These symptoms usually show up within 1 to 3 days of starting the antibiotic. In most cases, they disappear within 2 to 4 days after stopping the drug. But while they last, the person can become a danger to themselves-trying to pull out IV lines, wandering off, or refusing food and fluids.

The science behind this isn’t fully understood, but researchers believe fluoroquinolones interfere with brain chemistry. They block GABA-A receptors, which are the brain’s natural “brakes” for nerve activity. Without those brakes, neurons fire too much, causing chaos in thinking and perception. Some studies also suggest these drugs overstimulate NMDA receptors, which can lead to excitotoxicity-essentially, the brain gets overwhelmed by its own signals.

Who’s Most at Risk?

Not everyone who takes a fluoroquinolone will get delirium. But certain people are far more vulnerable:

• Age 65 or older-About 40% of hospitalized adults are in this group, and they’re 5 to 10 times more likely to experience neuropsychiatric side effects.
• Reduced kidney function-Levofloxacin is mostly cleared by the kidneys. If kidneys aren’t working well, the drug builds up in the blood, increasing brain exposure.
• Pre-existing cognitive issues-Even mild memory problems or early dementia raise the risk.
• High doses-Taking 750 mg of levofloxacin daily (instead of 500 mg) nearly doubles the chance of confusion.
• Other medications-Drugs that affect the brain, like benzodiazepines or anticholinergics, can make things worse.

One study found that nearly half of all hospital spending for older adults is tied to complications like delirium. And in many cases, it’s preventable.

Why Doctors Often Miss It

Here’s the problem: delirium doesn’t look like a typical drug reaction. There’s no rash, no vomiting, no fever. Just confusion. And since doctors are trained to look for infections, fever, or organ failure, the real culprit-the antibiotic-often slips through the cracks.

As Dr. Shamik Bhattacharyya from Harvard pointed out in a 2016 study, antibiotics aren’t the first thing physicians suspect when someone develops delirium. In his review of 391 cases, fluoroquinolones were responsible for 18% of all antibiotic-linked delirium-more than any other class. Yet most cases weren’t recognized until after the patient had been confused for days.

One nurse in a Halifax hospital told me about an 82-year-old woman who was admitted for a UTI, started on levofloxacin, and by day two was screaming about spiders crawling on the walls. The family thought she was having a stroke. The medical team thought it was dementia worsening. It wasn’t until someone asked, “Has she started any new meds?” that the real cause came to light. She was taken off the antibiotic, and within 36 hours, she was back to her normal self.

What to Do If You Suspect Fluoroquinolone-Induced Delirium

If an older adult starts acting strangely after beginning a fluoroquinolone, here’s what matters:

1. Stop the drug immediately. Don’t wait for a doctor’s approval. Call the prescribing provider right away. Most cases resolve within 48 hours of stopping.
2. Rule out other causes. Blood tests for electrolytes, glucose, and kidney function help. A brain scan or EEG might be needed to exclude stroke or seizures.
3. Switch antibiotics. Alternatives like amoxicillin, cefdinir, or trimethoprim-sulfamethoxazole are safer for older adults and just as effective for many infections.
4. Monitor closely. Even after stopping the drug, confusion can linger for a day or two. Keep the person safe-no unsupervised walking, no risky tasks.

The American Geriatrics Society’s 2023 Beers Criteria lists fluoroquinolones as “potentially inappropriate” for older adults unless no other options exist. That’s not a suggestion-it’s a warning.

Are There Safer Alternatives?

Yes. For most common infections in older adults, there are better choices:

• Urinary tract infections (UTIs): Nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin.
• Pneumonia: Amoxicillin-clavulanate, doxycycline, or macrolides like azithromycin.
• Sinus infections: Amoxicillin or doxycycline.

These drugs don’t cross the blood-brain barrier as easily. They don’t interfere with GABA receptors. And while they might take a little longer to work, they’re far less likely to cause sudden mental collapse.

Some hospitals have already changed their rules. At the University of California San Francisco, levofloxacin use for UTIs in patients over 70 dropped by 35% after they implemented strict guidelines requiring a second opinion before prescribing.

Why This Problem Is Getting Worse-And Better

Despite the risks, fluoroquinolones are still widely prescribed. In 2019, over 26 million prescriptions were filled in the U.S. But things are shifting. After the FDA issued stronger warnings in 2018, prescriptions for older adults dropped by 20.4% within two years. Hospitals are creating checklists, pharmacists are flagging high-risk patients, and family members are starting to ask the right questions.

Still, resistance is growing. The CDC reports that 35% of gonorrhea strains are now resistant to fluoroquinolones, making them useless for some infections. That’s why they’re not being retired-they’re being reserved.

Future solutions include smart prescribing tools that alert doctors when they try to order levofloxacin for an 80-year-old with kidney disease. Research is also looking at biomarkers that might predict who’s most likely to react badly. But for now, the best tool is awareness.

What Families and Caregivers Can Do

If you’re caring for an older relative:

• Always ask: “Is this antibiotic necessary? Are there safer options?”
• Know the signs of delirium: sudden confusion, hallucinations, agitation.
• Keep a list of all medications-including over-the-counter and supplements.
• If they start acting differently after starting a new antibiotic, don’t wait. Call the doctor immediately.

Delirium isn’t just uncomfortable-it increases the risk of falling, hospital readmission, long-term cognitive decline, and even death. But when caught early, it’s reversible. That’s the difference between a few days of confusion and a lifetime of decline.