Week 3 - Myasthenia Gravis

Question 1

Describe what is Myasthenia Gravis

Question 2

Describe the pathophysiology of Myasthenia Gravis

Answer 2

• Caused by impaired neuromuscular junctions from antibodies acting against ( autoimmune reaction ) self nicotinic Acetylcholine receptors
• Loss of receptors means there is less transmission (from Acetylcholine binding) across the synapsw and therefore decreased sodium into cell decreased amount of action potential increasing muscle relaxation

Question 3

Describe the function of Acetylcholinesterase in Myasthenia Gravis

Answer 3

Acetylcholinesterase breaks down acetylecholine by the post synaptic cleft therefore meaning there is decreased amoutn of acetylcholine and therefore transmissions —> action potential meaning increased muscle contraction

Question 4

Describe the moa of Acetylcholine esterase inhibitors

Answer 4

• Inhibiting Acetylcholine esterase means AChe is left longer in the synaps allowing it to bind to a nicotinic receptor and transmission is passed

Question 5

What drugs are examples as cholinesterase inhibitors

Answer 5

Pyridostigmine - MG
Neostigmine - MG
Malathion - Head lice

Question 6

Describe the physiological effect Acetylcholinesterase inhibitors have on the body

Answer 6

Is parasympathomimetic meaning increases physioogical effects of parasympathetic pathway

e.g decreased heart rate

• contraction of smooth muscle
• pupil constriction

Question 7

Describe some triggers for MG

Answer 7

• Infection
  Thyroid function
• stress
• anaemia

Question 8

Name Some drugs that contraindicate MG for their interference with nueromuscle transmission

Answer 8

Phenytoin
carbamazepine
Lithium
Antimuscarinic agenst
lidocaine

Question 9

Name Some drugs that contraindicate MG for their increase in muscle weakness

Answer 9

• Beta BLockers
• Diuretics
  Statins
  Magnesium

Question 10

Describe the treatment for MG

What is the maintenance dose of pyridostigmine ?

Answer 10

Pyridostigmine

starting 15mg QDS with food

Maintenance dose is 60mg

Question 11

Describe the adverse effects of pyridostigmine

Answer 11

Pyridostimine is a parasympathomimetic so has nicotinic and muscarinic affects including :

• Muscle / abdominal cramps
• Gut motility increases ( diarrohea)
• bradycardia
• bronchial constriction
  increased sweating

Question 12

What is the drug treatment provided for side effect control ?

Answer 12

• Diarrhoea - Loperamide
• Taking with food can mitigate GI s/e
• Co-prescribing oral anti-cholinergic drugs (that have little or no effect on nicotinic
  receptors (i.e. do not produce muscle weakness)