Fluoroquinolones and Delirium in Older Adults: What You Need to Know About Cognitive Side Effects

When an older adult starts feeling confused, disoriented, or sees things that aren’t there, most people assume it’s dementia, a stroke, or just aging. But sometimes, the cause is something much simpler-and far more preventable-a common antibiotic. Fluoroquinolones, a class of drugs like levofloxacin and ciprofloxacin, are prescribed millions of times each year in the U.S. for infections like pneumonia, urinary tract infections, and sinusitis. But for people over 65, these antibiotics can trigger sudden, frightening cognitive changes known as delirium. And it happens faster than you think.

What Are Fluoroquinolones, and Why Are They So Common?

Fluoroquinolones were developed in the 1960s and became widely used because they work against a broad range of bacteria. They’re strong, convenient (often just one pill a day), and effective. That’s why doctors reach for them. In 2019, about 27 million fluoroquinolone prescriptions were filled in the U.S. alone. But their popularity doesn’t mean they’re safe for everyone.

Drugs like levofloxacin, a fluoroquinolone antibiotic commonly prescribed for respiratory and urinary infections, ciprofloxacin, used for infections like kidney infections and anthrax exposure, and moxifloxacin, often used for pneumonia and abdominal infections are all part of this class. They work by breaking bacterial DNA, stopping infections in their tracks. But that same mechanism can also interfere with brain chemistry.

How Do Fluoroquinolones Cause Delirium?

Delirium isn’t just being forgetful. It’s a sudden, severe confusion that comes on over hours or days. People may not know where they are, can’t focus on a conversation, hear voices, or become agitated. In older adults, this isn’t rare-it’s underdiagnosed.

Fluoroquinolones disrupt the brain’s natural balance of neurotransmitters. They block GABA-A receptors, which normally calm brain activity. When those receptors are inhibited, the brain gets overexcited. Think of it like removing the brakes from a car. The result? Hallucinations, memory loss, and confusion. Some studies also suggest these drugs overstimulate NMDA receptors, adding to the chaos.

The risk isn’t theoretical. A 2016 review of 391 patients with antibiotic-induced delirium found that fluoroquinolones were responsible for nearly 18% of cases-more than any other antibiotic class. That’s not a small number. It’s one of the top triggers.

Who’s Most at Risk?

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

• Age 65 and older - Nearly half of hospitalized adults are over 65, and their brains are more sensitive to drug changes.
• Reduced kidney function - About 85% of levofloxacin leaves the body through the kidneys. If kidneys aren’t working well, the drug builds up. A creatinine clearance under 50 mL/min doubles the risk.
• Pre-existing brain conditions - People with dementia, Parkinson’s, or a history of stroke are at higher risk.
• High doses - Taking 750 mg of levofloxacin daily (instead of 500 mg) increases the chance of cognitive side effects.
• Multiple medications - Mixing fluoroquinolones with steroids, antidepressants, or antipsychotics can amplify the effect.

One case report in the Journal of Clinical Pharmacy and Therapeutics described an 82-year-old woman with mild kidney disease who developed vivid hallucinations and severe disorientation after just two days on 750 mg of levofloxacin. She had no prior history of mental illness. Her symptoms vanished within 48 hours after stopping the drug.

How Fast Does It Happen-and How Fast Does It Go Away?

Delirium from fluoroquinolones doesn’t creep in slowly. It hits fast. Most patients start showing signs within 1 to 3 days of starting the antibiotic. The symptoms can be dramatic: confusion, inability to follow conversations, seeing people who aren’t there, hearing whispers, or becoming aggressive.

The good news? It’s usually reversible. Once the drug is stopped, most patients return to their baseline within 48 to 96 hours. In one documented case, a 76-year-old man with normal cognition became completely disoriented on day three of ciprofloxacin. His family thought he was having a stroke. After the antibiotic was discontinued and his labs checked, everything cleared up in two days.

This reversibility is critical. It means that if you catch it early, you can prevent long-term damage. But if you don’t recognize it, the patient might end up in a psychiatric ward, get labeled with dementia, or even be placed in a nursing home.

Why Do Doctors Keep Prescribing Them?

It’s not that doctors are careless. Many simply don’t know this side effect exists-or they don’t think it applies to their patient. The American Academy of Neurology has pointed out that antibiotics are rarely the first thing doctors suspect when someone develops delirium. Blood tests, brain scans, and heart checks come first. Fluoroquinolones? Not on the radar.

And here’s the catch: these drugs are often prescribed for infections that don’t even need them. The CDC says fluoroquinolones are overused for simple urinary tract infections, bronchitis, and sinusitis-conditions that could be treated with safer antibiotics like nitrofurantoin, a first-line antibiotic for uncomplicated UTIs in older adults or amoxicillin, a beta-lactam antibiotic with low CNS penetration and minimal delirium risk.

Since the FDA’s 2018 safety warning, prescribing has dropped by about 20% in older adults. Hospitals like UCSF have cut levofloxacin use for UTIs by 35% after implementing protocols to avoid it in seniors. But many outpatient clinics still default to fluoroquinolones because they’re easy to prescribe.

What Should You Do If You or a Loved One Is Prescribed One?

If you’re over 65-or caring for someone who is-ask these questions before filling the prescription:

1. Is this infection serious enough to need a fluoroquinolone?
2. Are there safer alternatives like nitrofurantoin, amoxicillin, or trimethoprim-sulfamethoxazole?
3. What’s my kidney function? Can we check my creatinine clearance?
4. Will you start me on the lowest effective dose?
5. What signs of confusion should I watch for in the first 72 hours?

If the answer to any of these is “I don’t know” or “It’s fine,” push back. The FDA now says fluoroquinolones should be reserved for infections with no other treatment options. That’s not a suggestion-it’s a directive.

What Happens If Delirium Is Missed?

Delirium isn’t just uncomfortable-it’s dangerous. Studies show that older adults who develop delirium are more likely to:

• Stay in the hospital longer
• Need long-term care instead of going home
• Have a higher risk of death within a year

One study found that delirium increases the risk of nursing home placement by 50%. That’s not just a medical issue-it’s a life-altering one. And it’s often preventable.

When delirium is recognized early, the outcome is usually excellent. But if it’s mistaken for dementia or depression, the patient might be given antipsychotics-drugs that can make things worse. That’s why awareness matters.

What Are the Alternatives?

There are plenty of antibiotics that work just as well-with far less risk to the brain:

Even when fluoroquinolones are necessary-for example, in severe infections like pyelonephritis or complicated UTIs-doctors should start with lower doses and monitor closely.

What’s Being Done to Fix This?

Change is happening, but slowly. The American Geriatrics Society added fluoroquinolones to its 2023 Beers Criteria-a list of medications that are potentially harmful for older adults. That means hospitals and insurers are now required to justify their use.

Some institutions are using electronic alerts that pop up when a doctor tries to prescribe levofloxacin to a patient over 70 with kidney disease. Others are requiring second opinions before prescribing fluoroquinolones to seniors.

Researchers are also looking for biomarkers-blood tests or brain scans-that could predict who’s most likely to have a reaction. That’s still in early stages, but it could one day make prescribing much safer.

For now, the best tool is awareness. If you’re an older adult or caring for one, know the signs. If you notice sudden confusion after starting an antibiotic, stop the drug and call your doctor immediately. Don’t wait. Don’t assume it’s “just aging.”

Fluoroquinolones have saved lives. But they’re not harmless. For older adults, the cost of convenience can be too high. The next time you or someone you love is prescribed one, pause. Ask the questions. Demand alternatives. Because sometimes, the most dangerous thing in the medicine cabinet isn’t the infection-it’s the cure.