Conditions and symptoms
What Is Myasthenia Gravis? Muscle Weakness and Medicines
Myasthenia gravis · say it: my-us-THEE-nee-uh GRAV-isAlso written: MG, myasthenia
Short answer
Myasthenia gravis is a long-term condition where the immune system blocks nerve signals to muscles, causing weakness that worsens with use.
What it means
Myasthenia gravis (MG) is an autoimmune condition. The immune system makes antibodies that block messages between nerves and muscles. This causes muscle weakness that gets worse with use and improves with rest. It often affects the eyes (drooping eyelids, double vision), face, swallowing and speech, and sometimes the arms, legs and breathing muscles. Sudden trouble breathing or swallowing is an emergency.
Labels for several medicines warn that they can make myasthenia gravis worse, sometimes seriously. These include fluoroquinolone and some other antibiotics, some heart medicines, magnesium given into a vein, some anaesthetic drugs and others. The warning is telling people with MG to make sure every prescriber and pharmacist knows about it, and telling them to seek urgent help if weakness or breathing worsens after a new medicine.
Myasthenia gravis is different from general tiredness or muscle weakness from other causes, such as myopathy, where the muscle itself is affected.
Where you may see it
- Fluoroquinolone antibiotic boxed warnings
- 'Use with caution in myasthenia gravis' in prescribing information
- Neurology letters and medical alert records
📄 How it looks on a report
Fluoroquinolones may exacerbate muscle weakness in patients with myasthenia gravis. Avoid in patients with known history of myasthenia gravis.
🙅 What it does not mean
- It is not caused by being unfit or tired.
- A label warning does not mean every medicine is off-limits; many are fine.
- It is not the same as muscle damage (myopathy).
🗒️ Questions to ask your doctor
💊 Medicines whose labels mention “Myasthenia gravis”
Plain-English explanations of each medicine, from its official FDA label.
- Azithromycin
a macrolide antibacterial (antibiotic) medicine
- Ciprofloxacin
a fluoroquinolone antibacterial medicine
- Diazepam
A benzodiazepine, a type of medicine that slows activity in the central nervous system (brain and spinal cord)
- Levofloxacin
an antibiotic of the fluoroquinolone type
- Prednisone
a corticosteroid, a type of steroid medicine that works like the adrenocortical (adrenal gland) steroids the body makes naturally
- Simvastatin
a cholesterol-lowering medicine of the HMG-CoA reductase inhibitor type (often called a statin)
- Zolpidem Tartrate
a sleep medicine of the imidazopyridine class. The label describes it as a GABA A receptor positive modulator.
🔗 Read more from trusted sources
- “Myasthenia gravis” on MedlinePlus ↗
US National Library of Medicine
- NCI Dictionary definition ↗
US National Cancer Institute: “myasthenia gravis”
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