From the Guidelines
Amoxicillin is generally considered safe for patients with a history of myasthenia gravis (MG). Unlike some antibiotics such as fluoroquinolones, aminoglycosides, and macrolides that can worsen MG symptoms, amoxicillin (a penicillin-class antibiotic) does not typically exacerbate MG or interact with common MG medications. The British Thoracic Society guideline for bronchiectasis in adults 1 recommends amoxicillin as a first-line treatment for various infections, including those caused by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, without any specific caution or contraindication for patients with MG.
- Key points to consider when prescribing amoxicillin to patients with MG include:
- Standard dosing of amoxicillin can be used as appropriate for the infection being treated, typically 500 mg three times daily for adults, as recommended by the guideline 1.
- Adjustments may be necessary for renal function if necessary.
- Monitoring for any unusual worsening of MG symptoms when starting any new medication, even those considered safe, is crucial.
- The patient's increased susceptibility to infections due to immunosuppressant use for MG management should be considered, making prompt and appropriate antibiotic therapy particularly important. The reason amoxicillin is generally well-tolerated in MG patients is that it does not significantly affect neuromuscular transmission or acetylcholine receptors, which are central to MG pathophysiology, although this specific information is not mentioned in the provided guideline 1.
From the Research
Amoxicillin and Myasthenia Gravis (MG)
- Amoxicillin is generally considered safe for patients with MG, as it is a penicillin antibiotic [ 2 ].
- However, there have been reports of MG exacerbations after amoxicillin treatment, with symptoms starting a few days after antibiotic administration [ 2 ].
- A study found that 6 patients with MG developed acute worsening of symptoms after amoxicillin or amoxicillin/clavulanate treatment, requiring therapeutic intervention and resulting in full recovery to baseline neurological conditions within 1-2 months [ 2 ].
MG Exacerbations and Antibiotics
- The frequency and severity of MG exacerbations associated with the use of certain antibiotics, including ciprofloxacin, levofloxacin, and azithromycin, have been investigated [ 3 ].
- Amoxicillin usage was chosen for comparison, and the results showed that MG exacerbation was seen in 8/603 (1.3%) episodes of amoxicillin use, without a significant difference in frequencies of exacerbations among the four antibiotics [ 3 ].
- Underlying infection may play a role in MG exacerbations, and decision-making regarding the use of these antibiotics should be individualized [ 3 ].
MG Pathophysiology and Clinical Manifestations
- MG is an autoimmune neurological disorder characterized by defective transmission at the neuromuscular junction [ 4 ].
- The core clinical manifestation of MG is fatigable muscle weakness, which may affect ocular, bulbar, respiratory, and limb muscles [ 4 ].
- Clinical manifestations vary according to the type of autoantibody and whether a thymoma is present [ 4 ].
- Diagnosis is straightforward in most patients with typical symptoms and a positive antibody test, although a detailed clinical and neurophysiological examination is important in antibody-negative patients [ 5 ].