Myasthenia Gravis & Drug Interactions


If you have myasthenia gravis, it’s not unusual to be taking multiple medications. How do those drugs interact with drugs for infection, pain, or other illnesses, or with the over-the-counter (OTC) medications and supplements that can be found in most people’s medicine chests?

The topic of “Myasthenia Gravis and Drug Interactions” was addressed at Conquer MG’s October 2016 patient seminar in Oak Lawn, Illinois. Our speaker was Mitra Habibi, PharmD, from the University of Illinois at Chicago College of Pharmacy. Doctor Habibi is a clinical pharmacist; she works with physicians to coordinate care and medications for patients in the hospital setting. She also teaches at the University.

Click to see a short clip from Dr. Habibi’s presentation that covers cautions for MG patients regarding antibiotics, including black box warnings.

Click to see Dr. Habibi’s full presentation covering black box warnings; the use of antibiotics, pain medication, magnesium, statins, over-the-counter medications, and quinine for MG patients; and steroid side effects.

Here are highlights from Dr. Habibi’s presentation.

General Cautions

  • Avoid combining your meds in an old pill bottle; the label will be inaccurate and confusing for others.
  • Always keep an up-to-date list of your medications and doses in your wallet. That way you can share consistent and complete information with all of your health care providers.
  • To avoid drug interaction problems, it’s essential that each of your doctors has an accurate picture of all medications you’re taking, including over-the-counter (OTC) meds and herbal supplements.
  • OTC meds and supplements are drugs and can trigger interactions with other medications you take.
  • As we age, our bodies – including the liver and kidneys – metabolize drugs differently. So doses need to change.

Medications that Can Worsen MG Weakness

Antibiotics are the biggest classification of drugs that potentially cause problems in patients with MG. There are classes of antibiotics that can be used for MG patients and classes that should not be used. Key: your prescribing doctor should be aware that you have MG.

  • Never use someone else’s leftover antibiotics (even if you think you have the same illness), because you may be unaware of adverse effects with your MG or your other medications.
  • Medications labeled with black box warnings related to myasthenia gravis should be avoided. The Food and Drug Administration (FDA) requires this strictest warning when there is significant risk of serious or life-threatening side effects. The warning is surrounded by a black outline on the prescription container and insert.
  • These antibiotics have black box warnings and should not be used for individuals with myasthenia gravis:
    • Fluoroquinolones (Ciprofloxacin (“Cipro”), levofloxacin, gatifloxacin, femifloxacin, norfloxacin, ofloxacin)
    • Ketek (telithromycin)
  • These antibiotics should also be avoided because they can cause neuromuscular weakness.
    • Aminoglycosides (amikacin, gentamicin, kanamycin, neomycin, streptomycin, tobramycin)
    • Tobramycin – probably the weakest neuromuscular blocking effect (least problematic)
    • Macrolies (erythromycin, zithromycin or z-pack) – use cautiously, if at all
  • Clindamycin – Likely to worsen MG
  • These antibiotics have not been shown to cause many problems for MG patients
    • Tetracycline (doxycycline, minocycline) – this may worsen MG
    • Sulfonamides (Bactrim), Penicillin – causes rare cases, usually not a problem for majority of MG patients
  • Voriconazole (antifungual) and peramivir (antiviral) reported to worsen MG
  • Botulinum toxin (Botox) – avoid use

Other Topics

Dr. Habibi also noted:

  • Magnesium can interfere with neuromuscular transmission. The usual doses of medications containing magnesium (antacids, laxatives) are unlikely to cause problems – except in patients with kidney disease. The amount of magnesium in daily multivitamins is unlikely to cause problems. However, intravenous doses of magnesium sulfate can cause serious muscle weakness and should be avoided in MG patients.
  • The effect of Beta blockers on myasthenia gravis depends on the dose and type of medication. Propranolol is the most likely offender to cause fatigue, while Atenolol is least likely.
  • Steroids, commonly used to treat MG weakness, can have many adverse effects.
  • With pain management, it’s important to consider the individual to minimize drug interactions. Your doctor should take into account the severity of your MG disease, other complicating illnesses, and other medications being used before recommending pain meds. In general, aspirin, non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen, and acetaminophen (Tylenol) are considered safe for MG, that is, they have not been shown to worsen MG or cause muscle weakness. However, each of these medications carry risks (for example, NSAIDS can increase the risk of stomach ulcers when taken with steroids), so it’s important to view the individual situation.