Yes, certain antibiotics can cause seizures, though it’s uncommon. The risk is highest with specific drug classes, particularly when given at high doses or to people with kidney problems, and the seizures typically stop once the antibiotic is discontinued or the dose is adjusted.
How Antibiotics Trigger Seizures
Your brain maintains a careful balance between signals that excite nerve cells and signals that calm them down. The calming side relies heavily on a chemical messenger called GABA, which acts like a brake on brain activity. Several antibiotics interfere with this braking system. They block GABA receptors directly or reduce GABA production, which leaves nerve cells firing more easily than they should. Some antibiotics also activate excitatory receptors (the ones that speed up nerve signaling), further tipping the balance toward uncontrolled electrical activity. When enough neurons fire simultaneously without the usual checks in place, a seizure results.
Other mechanisms can contribute too: some antibiotics cause oxidative stress by generating toxic molecules inside nerve cells, interfere with protein production neurons need to function normally, or disrupt the energy-producing structures within cells. These effects lower what’s called the “seizure threshold,” the point at which abnormal electrical activity spills over into a full seizure.
Which Antibiotics Carry the Highest Risk
A systematic review covering 143 studies and more than 25,700 patients identified four groups of antibiotics most strongly linked to seizures: unsubstituted penicillins, fourth-generation cephalosporins, carbapenems (especially imipenem), and ciprofloxacin. The evidence connecting these drugs to seizures is still graded as low overall, meaning seizures remain a rare side effect even with these higher-risk medications. But the pattern across thousands of case reports is consistent enough to warrant caution.
Penicillins
Penicillin G has the most significant seizure-inducing potential in the penicillin family. When given intravenously to adults, it can harm the central nervous system at doses exceeding 50 million units in a 24-hour period. At typical therapeutic doses, the risk is much lower, but it climbs in patients whose kidneys can’t clear the drug efficiently.
Cephalosporins
Cefepime, a fourth-generation cephalosporin used for pneumonia, urinary tract infections, and skin infections, has drawn particular attention. The FDA has issued a safety communication about cefepime and seizure risk in patients whose doses aren’t adjusted for kidney function. Cefepime can cause a particularly dangerous form of seizure called nonconvulsive status epilepticus, where continuous seizure activity happens in the brain without the obvious jerking movements people associate with seizures. Instead, patients may become confused, unresponsive, or stuporous. In one reported case, a patient developed this condition after just five days on cefepime following recovery from kidney failure. Earlier-generation cephalosporins like cefazolin and cefuroxime have also been linked to neurotoxicity, but less frequently.
Carbapenems
Imipenem has long been considered the carbapenem most likely to cause seizures. Meropenem was developed partly as a safer alternative. In a large retrospective study of hospitalized infants, seizure diagnoses occurred at a rate of 3.0 per 1,000 days on imipenem compared to 2.3 per 1,000 days on meropenem. That looks like a meaningful difference, but after adjusting for other factors like illness severity, the statistical difference disappeared. Clinical guidelines for critically ill patients on kidney replacement therapy note that imipenem’s neurotoxicity risk is “significantly higher” at the doses sometimes needed for resistant infections, and recommend considering a different antibiotic altogether in those situations.
Fluoroquinolones
Ciprofloxacin and levofloxacin have both been implicated in seizures, though the evidence comes mainly from individual case reports rather than large studies. Fluoroquinolones vary in their seizure potential. Among older fluoroquinolones, trovafloxacin carried the greatest risk, while levofloxacin may carry the least. In one published case, a 74-year-old woman with no seizure history and no electrolyte abnormalities experienced a seizure after five doses of levofloxacin for pneumonia, suggesting the drug alone was responsible. In another case, a patient seized on levofloxacin and then again when switched to ciprofloxacin, though she also had low magnesium and impaired kidney function, both of which independently lower the seizure threshold.
Who Is Most at Risk
Kidney impairment is the single biggest risk factor. Most of the antibiotics linked to seizures are cleared from the body by the kidneys. When kidney function is reduced, the drug accumulates to higher levels in the blood and, eventually, the brain. Many reported cases of antibiotic-induced seizures involve patients who either had unrecognized kidney problems or whose antibiotic doses weren’t reduced to match their kidney function.
Other factors that increase risk include:
- Pre-existing brain conditions: prior seizure disorders, brain tumors, strokes, or meningitis can all make the brain more susceptible
- Electrolyte imbalances: low magnesium and low sodium both lower the seizure threshold and can combine with an antibiotic’s effects to trigger a seizure
- Other medications that lower seizure threshold: theophylline (used for lung disease) taken alongside ciprofloxacin is a well-documented combination
- High doses: the risk scales with how much drug reaches the brain, so aggressive dosing in critically ill patients increases exposure
Age plays an indirect role too. Older adults are more likely to have reduced kidney function (sometimes without knowing it) and are more likely to be on multiple medications that interact.
What Antibiotic-Induced Seizures Look Like
These seizures can look like any other seizure: generalized shaking, loss of consciousness, sudden muscle jerking. But one of the trickier presentations is nonconvulsive status epilepticus, where seizure activity is happening electrically in the brain but the outward signs are subtle. A person might seem confused, drowsy, or simply “not themselves” for hours or days. This is especially common with cefepime. The only way to confirm it is with an EEG, a test that records brain electrical activity. If an unexplained change in mental status develops while someone is on a high-risk antibiotic, that possibility needs to be investigated.
How These Seizures Are Treated
The most important step is stopping or changing the antibiotic. Because these seizures are caused by a drug rather than by epilepsy, removing the cause is often enough to prevent further episodes. In the acute setting, the same medications used for other seizures are effective. Fast-acting sedatives from the benzodiazepine family are the standard first response. If those don’t stop the seizure, stronger sedatives are used next.
One important distinction: a common anti-seizure medication used in epilepsy, phenytoin, does not work for drug-induced seizures and is not recommended. If the seizure was caused by a specific antibiotic used for tuberculosis called isoniazid, a form of vitamin B6 is the targeted treatment and can be lifesaving.
Most people who experience an antibiotic-induced seizure do not go on to develop epilepsy. The seizure is a direct toxic effect of the drug, and once the drug is cleared from the body, the risk returns to baseline. Recovery depends on how quickly the cause is identified and the antibiotic is stopped, but most patients recover fully without lasting neurological effects.
Reducing the Risk
Dose adjustments based on kidney function are the primary safeguard. For patients on kidney replacement therapies, clinical guidelines recommend using loading doses to achieve effective drug levels quickly, then adjusting maintenance doses downward to avoid toxic accumulation. For drugs with wide safety margins like most penicillins, slightly higher doses may be acceptable in critical illness, but for imipenem and cefepime, erring on the side of caution (or choosing an alternative antibiotic) is preferred when kidney function is compromised.
If you have a history of seizures, kidney disease, or known brain conditions, making sure your prescriber is aware before starting any antibiotic is the simplest way to reduce risk. These factors can influence which antibiotic is chosen and at what dose, avoiding the higher-risk options when equally effective alternatives exist.