Antibiotics and Myasthenia Gravis: What You Need to Know About Neuromuscular Weakness Risks

For someone living with myasthenia gravis (MG), even a simple infection can feel dangerous. Not just because the illness itself weakens muscles, but because the very drugs meant to treat it-antibiotics-might make things worse. This isn’t theoretical. It’s a real, documented risk that’s shaped how doctors choose treatments for millions of people with MG worldwide.

What Happens When Antibiotics Meet Myasthenia Gravis?

Myasthenia gravis is an autoimmune disorder where the body attacks the connection between nerves and muscles. Normally, nerves send signals using a chemical called acetylcholine. That chemical binds to receptors on muscle cells, telling them to contract. In MG, those receptors are damaged or blocked, so muscles don’t get the message properly. That’s why people with MG get tired easily, have drooping eyelids, trouble swallowing, or even breathing issues.

Now add antibiotics into the mix. Some of them interfere with that same nerve-muscle connection. They don’t cause MG, but they can make the symptoms much worse-sometimes suddenly and dangerously. This is called an MG exacerbation. In rare cases, it can lead to myasthenic crisis, where breathing muscles fail and emergency ventilation is needed.

Which Antibiotics Are Riskiest?

Not all antibiotics are created equal when it comes to MG. Some are relatively safe. Others carry serious warnings.

High-risk antibiotics:

• Aminoglycosides (like gentamicin, tobramycin): These are the worst offenders. They directly block acetylcholine receptors at the muscle end. Even a single dose can trigger weakness in sensitive patients. Many hospitals avoid them entirely in MG patients.
• Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin): These once had FDA black box warnings for MG patients. They can disrupt nerve signaling and have been linked to muscle weakness, tendon ruptures, and nerve damage. Studies show about 1.6% to 2.4% of MG patients experience worsening symptoms after taking them.
• Macrolides (azithromycin, clarithromycin, erythromycin): These are also flagged as risky. They interfere with calcium channels needed for acetylcholine release. About 1.5% of MG patients report flare-ups after use.
• Telithromycin: This antibiotic was pulled from the U.S. market in 2007 because it caused life-threatening MG exacerbations. It’s still a textbook example of what not to give.

Lower-risk antibiotics:

• Penicillins (amoxicillin, ampicillin, penicillin V): These are the go-to choices for most infections in MG patients. A 2024 Cleveland Clinic study of over 900 antibiotic courses found only a 1.3% exacerbation rate with penicillins-lower than fluoroquinolones and macrolides.
• Cephalosporins (cefazolin, cephalexin): Generally considered safe. No strong evidence links them to MG worsening.
• Vancomycin and clindamycin: Use with caution, but not as risky as aminoglycosides or fluoroquinolones. Often used when penicillins aren’t suitable.

Why Do Some Antibiotics Make MG Worse?

It’s not just one mechanism. Different antibiotics attack the neuromuscular junction in different ways:

• Presynaptic effects: Some antibiotics, like macrolides, reduce the release of acetylcholine from nerve endings. Less signal = weaker muscle response.
• Postsynaptic effects: Aminoglycosides bind directly to acetylcholine receptors, blocking the signal before it even reaches the muscle.
• Calcium channel interference: Fluoroquinolones can disrupt calcium flow in nerve cells, which is needed to trigger acetylcholine release.

In a healthy person, the body has plenty of spare receptor sites. But in MG, those sites are already reduced by 70-80%. Adding an antibiotic that further blocks or reduces signaling pushes the system past its limit. That’s when weakness spikes.

New Evidence Is Changing Old Rules

For years, doctors were told to avoid fluoroquinolones and macrolides entirely in MG patients. But a landmark 2024 study from Cleveland Clinic, involving 365 patients and 918 antibiotic courses, turned that advice on its head.

The study found that while fluoroquinolones and macrolides did cause exacerbations, the rate (2%) was only slightly higher than amoxicillin (1.3%). The difference wasn’t statistically significant. That means, for many patients, the risk isn’t as high as once thought.

What matters more is who you are. The study identified three key risk factors that make an MG patient far more vulnerable:

• Recent hospitalization or ER visit for MG in the past 6 months
• Being female
• Having diabetes

If you have none of these, your risk from a fluoroquinolone or macrolide is likely low. But if you have one or more? You need a much more cautious approach.

When Infection Is the Real Enemy

Here’s the tricky part: infections themselves trigger MG flares in 88.2% of cases where antibiotics were blamed. That means the weakness you see after taking an antibiotic might actually be from the pneumonia, UTI, or sinus infection you’re trying to treat.

That’s why doctors don’t always avoid risky antibiotics. Sometimes, the infection is too dangerous to delay. A severe lung infection can kill faster than antibiotic-induced weakness. The goal isn’t to avoid antibiotics entirely-it’s to choose the safest one and monitor closely.

What Should You Do as a Patient?

If you have MG, here’s what works in real life:

• Always tell every doctor and pharmacist you have MG. Write it on your phone’s lock screen. Tell your pharmacy when you fill prescriptions. Many ER visits are worsened because no one knew the patient had MG.
• Ask: “Is there a safer antibiotic for someone with MG?” Don’t assume the first one prescribed is the best. Penicillins are often just as effective for common infections.
• Monitor for warning signs in the first 72 hours. If you start feeling more tired than usual, your eyelids droop more, your voice gets weak, or swallowing becomes harder-call your neurologist immediately. Don’t wait.
• Keep your MG specialist in the loop. Even if your primary doctor prescribes the antibiotic, check with your MG team first. They know your history best.
• Don’t skip antibiotics if you’re sick. Untreated infections are far more dangerous than the small risk from most antibiotics. The key is smart selection and close watch.

What About Other Medications?

Antibiotics aren’t the only drugs that can worsen MG. Beta-blockers, some anti-seizure meds, magnesium IV, and even certain over-the-counter antacids with magnesium can be risky. Always review every medication-even supplements-with your MG specialist.

Bottom Line: It’s About Risk, Not Fear

The old rule-“avoid all fluoroquinolones and macrolides”-is outdated. The new rule? Assess the patient, not just the drug.

For most MG patients with stable disease, penicillins are still the safest bet. But if you need a fluoroquinolone for a stubborn infection, and you’re not in the high-risk group, it might be okay-with monitoring.

The biggest mistake isn’t using a risky antibiotic. It’s not treating an infection at all because you’re afraid. Infections kill. MG flares, when caught early, can be managed.

Stay informed. Stay in touch with your care team. And remember: you’re not powerless. You have the power to ask the right questions, to speak up, and to choose safety without surrendering to fear.