Parkinson's Disease & Myasthenia Gravis Flashcards
What is the MOA of levodopa?
Crosses the BBB and is converted to dopamine by dopa decarboxylase.
Which enzyme converts L-DOPA to dopamine?
DOPA decarboxylase
Which enzyme normally metabolises dopamine?
Monoamine oxidase B
Why is L-DOPA more effective in the early stages of Parkinson’s, then becomes less effective?
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.
What are co-careldopa and co-beneldopa?
Combination drugs that contain both L-DOPA and a peripheral DOPA decarboxylase inhibitor, this increases the amount of dopamine entering the brain.
Name a dopamine receptor agonist.
Amantadine
Name some side effects of dopamine receptor agonists.
- dopamine dysregulation syndrome
- more psychiatric side effects than levodopa
- sedation
- hallucinations
- nausea
- confusion
What is dopamine dysregulation syndrome?
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.).
What are rasagiline and selegiline used for?
Monoamine oxidase B inhibitors used for Parkinson’s - enhance dopamine by preventing dopamine metabolism, reducing motor problems.
What is the MOA of COMT inhibitors?
Cathechol-O-methyl transferase inhibitors - reduce the peripheral breakdown of L-DOPA, are only effective if given with L-DOPA.
Name a COMT inhibitor used for Parkinson’s disease.
Entacapone
What is the MOA of anticholinergic when given for Parkinson’s?
Block ACh receptors, reducing tremor (but has no effect on bradykinesia).
What are orphenadrine and procyclidine?
Anticholinergics used for Parkinson’s disease.
When would deep brain stimulation be used for Parkinson’s?
- in someone who is responsive to L-DOPA but can’t tolerate it due to side effects
- must not be given to psychotic patients
What is Myasthenia Gravis?
An autoimmune disease when antibodies block neuromuscular junctions of skeletal muscle, leading to muscle weakness.
How does someone with myasthenia gravis commonly present?
- drooping eyelids
- trouble walking and talking
- double vision
Which type of Ach receptors are found at neuromuscular junctions?
Nicotinic receptors.
What medication can be used for Myasthenia Gravis?
Acetylcholinesterase inhibitors - reduce ACh breakdown and enhance neuromuscular transmission.
Name 2 acetylcholinesterase inhibitors.
Pyridostigmine
Neostigmine
Name some drugs that can exacerbate Myasthenia gravis.
- beta blockers
- calcium channel blockers
- ACEi
- aminoglycosides
What is a Myasthenic crisis?
An acute exacerbation of myasthenia gravis when the muscles are very weak - the patient needs to be NBM due to an unsafe swallow.
What is a cholinergic crisis?
When someone has a neuromuscular block caused by overtreatment with acetylcholinesterase inhibitors.
Apart from acetylcholinesterase inhibitors, what other medication is used in the treatment of myasthenia gravis?
- corticosteroids - decrease immune response
- steroid sparing drugs e.g. Azathiprine
- plasmapheresis
