Parkinson's Disease & Myasthenia Gravis

Question 1

What is the MOA of levodopa?

Answer 1

Crosses the BBB and is converted to dopamine by dopa decarboxylase.

Question 2

Which enzyme converts L-DOPA to dopamine?

Answer 2

DOPA decarboxylase

Question 3

Which enzyme normally metabolises dopamine?

Answer 3

Monoamine oxidase B

Question 4

Why is L-DOPA more effective in the early stages of Parkinson’s, then becomes less effective?

Answer 4

L-DOPA is taken up by dopaminergic cells in the substantia nigra and converted to dopamine in these - it is more effective when there are more dopaminergic cells.

Question 5

What are co-careldopa and co-beneldopa?

Answer 5

Combination drugs that contain both L-DOPA and a peripheral DOPA decarboxylase inhibitor, this increases the amount of dopamine entering the brain.

Question 6

Name a dopamine receptor agonist.

Answer 6

Amantadine

Question 7

Name some side effects of dopamine receptor agonists.

Answer 7

• dopamine dysregulation syndrome
• more psychiatric side effects than levodopa
• sedation
• hallucinations
• nausea
• confusion

Question 8

What is dopamine dysregulation syndrome?

Answer 8

An impulse control disorder where someone has the following symptoms due to excess dopamine: pathological gambling, hypersexuality, compulsive shopping, desire to increase dosage and pounding (sorting into colours, sizes, shapes etc.).

Question 9

What are rasagiline and selegiline used for?

Answer 9

Monoamine oxidase B inhibitors used for Parkinson’s - enhance dopamine by preventing dopamine metabolism, reducing motor problems.

Question 10

What is the MOA of COMT inhibitors?

Answer 10

Cathechol-O-methyl transferase inhibitors - reduce the peripheral breakdown of L-DOPA, are only effective if given with L-DOPA.

Question 11

Name a COMT inhibitor used for Parkinson’s disease.

Answer 11

Entacapone

Question 12

What is the MOA of anticholinergic when given for Parkinson’s?

Answer 12

Block ACh receptors, reducing tremor (but has no effect on bradykinesia).

Question 13

What are orphenadrine and procyclidine?

Answer 13

Anticholinergics used for Parkinson’s disease.

Question 14

When would deep brain stimulation be used for Parkinson’s?

Answer 14

• in someone who is responsive to L-DOPA but can’t tolerate it due to side effects
• must not be given to psychotic patients

Question 15

What is Myasthenia Gravis?

Answer 15

An autoimmune disease when antibodies block neuromuscular junctions of skeletal muscle, leading to muscle weakness.

Question 16

How does someone with myasthenia gravis commonly present?

Answer 16

• drooping eyelids
• trouble walking and talking
• double vision

Question 17

Which type of Ach receptors are found at neuromuscular junctions?

Answer 17

Nicotinic receptors.

Question 18

What medication can be used for Myasthenia Gravis?

Answer 18

Acetylcholinesterase inhibitors - reduce ACh breakdown and enhance neuromuscular transmission.

Question 19

Name 2 acetylcholinesterase inhibitors.

Answer 19

Pyridostigmine

Neostigmine

Question 20

Name some drugs that can exacerbate Myasthenia gravis.

Answer 20

• beta blockers
• calcium channel blockers
• ACEi
• aminoglycosides

Question 21

What is a Myasthenic crisis?

Answer 21

An acute exacerbation of myasthenia gravis when the muscles are very weak - the patient needs to be NBM due to an unsafe swallow.

Question 22

What is a cholinergic crisis?

Answer 22

When someone has a neuromuscular block caused by overtreatment with acetylcholinesterase inhibitors.

Question 23

Apart from acetylcholinesterase inhibitors, what other medication is used in the treatment of myasthenia gravis?

Answer 23

• corticosteroids - decrease immune response
• steroid sparing drugs e.g. Azathiprine
• plasmapheresis