Pharmacology: Myasthenia Gravis

Question 1

What is the pathophysiology of myasthenia gravis?

Answer 1

Ach has difficulty binding to Ach receptors due to IgG blocking the receptor site. Ach gets broken down before it can bind to the post-synaptic receptor

Question 2

What signs and symptoms do patients with myasthenia gravis experience?

Answer 2

Fluctuating FATIGUABLE weakness of skeletal muscle:

• eyelid dropping is the most common presentation
• dysphagia, dysphonia, dysarthria
• limb weakness
• can have respiratory muscle involvement which can be fatal eg aspiration pneumonia

Question 3

Name some drugs that can exacerbate myasthenia gravis?

Answer 3

• aminoglycosides
• beta-blockers
• magnesium
• ACEI

Question 4

What are some complications of myasthenia gravis?

Answer 4

Can get a myasthenic crisis - weak all over, nasal speech, resp muscles can be involved

Overtreatment can cause a cholinergic crisis, need to protect airway

Question 5

List the therapeutic managements of myasthenia gravis

Answer 5

• acetylcholinesterase inhibitors
• corticosteroids to decrease immune response
• steroid sparing drugs eg azathioprine
• IV immunoglobulin
• plasmapheresis to reduce AchR antibodies for short term improvement

Question 6

How do acetylcholinesterase inhibitors work?

Answer 6

They enhance neuromuscular transmission by reducing breakdown of Ach.
Needs to be given before food to prevent aspiration
Excess dose can cause cholinergic crisis

Question 7

What are the side effects of cholinergics?

Answer 7

Miosis and SSLUDGE

• Salivation
• Sweating
• Lacrimation
• Urinary incontinence
• Diarrhoea
• GI upset
• Emesis