Parkinson's Flashcards
What is Parkinson’s characterised by?
Loss of dopaminergic neurons in the substantia nigra, the region of the brain responsible for modulating motor movement and reward functions, as well as being involved in dopamine production.
What are the common symptoms of Parkinson’s?
Tremors
Stiffness
Slowness
Balance issues
What is first line treatment of Parkinson’s?
Levodopa
How does levodopa work?
Crosses blood brain barrier and acts as a dopamine precursor in the presynaptic terminals of dopaminergic neurons, resulting in decarboxylation to form dopamine.
What are “on-off” periods in levodopa and other Parkinson’s treatment?
Diphasic dyskinesia - 2 “off” periods of erratic movements, first when levodopa is first given and when it wears off.
What can be done to improve end-of-dose deterioration and on-off periods?
Change timing of doses
Increase the dose
Add in other medicines
What is a key complication of levodopa?
Dopamine dysregulation syndrome - impulse control disorders such as pathological gambling, binge eating, and hypersexuality.
What is levodopa often combined with?
Dopa decarboxylase inhibitors such as:
Benserazide (co-beneldopa)
Carbidopa (co-careldopa)
How do dopa decarboxylase inhibitors work?
They inhibit aromatic amino acid decarboxylase (AAAD) outside the brain to prevent premature decarboxylation of levodopa to dopamine before it penetrates the BBB.
What are some of the main side effects caused by levodopa?
Nausea and vomiting
Hypotension
Anxiety and depression
Hallucinations (mainly with changes in dose)
How do dopa decarboxylase inhibitors reduce nausea and vomiting caused by levodopa?
Premature decarboxylation of levodopa to dopamine can result in activation of dopamine receptors in the gut and therefore nausea and vomiting. These medicines prevent this premature decarboxylation.
How should a patient be transferred from one levodopa/dopa-decarboxylase inhibitor preparation to another?
Discontinue previous preparation 12 hours before starting next one. Avoid abrupt withdrawal due to risk of neuroleptic malignant syndrome and rhabdomyolysis (muscle break down).
How do dopamine agonists work?
Mimic dopamine by selectively stimulating D2 receptors in the brain.
Why are dopamine receptor agonists second-line to levodopa?
They are less effective at improving motor symptoms and the ability to do day-to-day tasks and they have an increased risk of hallucinations.
What are the 2 types of dopamine agonists?
Ergot - bromocriptine, pergolide, cabergoline. Associated with increased risk of heart and lung problems.
Non-ergot - ropinirole, rotigotine, apomorphine. Newer and safer.
How do COMT inhibitors work?
Inhibit catechol-O-methyl transferase (COMT) to prevent peripheral breakdown of levodopa, allowing more of it to reach the brain.
When would a COMT inhibitor be prescribed?
As an adjunct treatment with levodopa if a patient develops dyskinesia or motor fluctuations.
Name 1 COMT inhibitor.
Entacapone.
How do MAO-B inhibitors work?
Inhibit monoamine oxidase B (MAO-B) to prevent removal of “excess” dopamine from the brain.
Name 3 MAO-B inhibitors.
Safinamide
Isocarboxazid
Phenelzine
When would a MAO-B inhibitor be prescribed?
As an adjunct treatment with levodopa if a patient develops dyskinesia or motor fluctuations.
Why would an anti-emetic be prescribed to a Parkinson’s patient?
Many antiparkinson’s medication, such as levodopa, can cause nausea and vomiting due to stimulation of dopamine receptors in the gut.
What anti-emetics could you prescribe to a Parkinson’s patient?
Low dose domperidone (10mg tds) for maximum 1 week (stop when nausea resolves).
How does domperidone work?
Dopamine D2 receptor antagonist which works by:
1. inhibiting dopamine receptors involved in emesis in the chemoreceptor trigger zone
2. inhibiting dopamine receptors in the gut to prevent dopamine slowing gastric motility (causes nausea and vomiting) i.e., speeds up gastric motility
What is a common side effect of domperidone?
Dry mouth
What anti-emetics cannot be used in Parkinson’s and why?
Metoclopramide and prochlorperazine.
They are dopamine antagonists, same as domperidone, but they cross the BBB at a much higher rate where they can cause extrapyramidal side effects, even in those without Parkinson’s.
What are critical medicines?
Ones that cannot be easily be replaced by other medicines and if it is omitted it could cause serious harm to the patient.
Why are anti-Parkinson’s medicines considered critical medicines?
Parkinson’s medicines are extremely time critical due to end-of-dose deterioration and on-off periods. If a dose is late or missed the patient will start to experience Parkinson’s symptoms e.g., tremor, confusion, agitation, difficulty communicating.
What should you recommend if a person forgets to take their Parkinson’s medication?
Take it as soon as they remember and adjust the subsequent doses that day. Do not take 2 doses together.
Why are swallowing issues common in Parkinson’s?
Swallowing can be affected by rigidity of muscles in the face, jaw, and tongue.
What solutions are there to swallowing difficulties?
Adjust patients position and head posture.
Take smaller bites when eating
Change diet to softer foods and thicker drinks.
Use an enteral feeding tube.
How can Parkinson’s medication be given via enteral feeding tube
Co-beneldopa - dispersible tablets available
Co-careldopa - regular tablets can be dispersed in 10ml of water.
Entacapone - regular tablets can be dispersed in 10ml of water.
Ropinirole - regular tablets can be dispersed in 10ml of water.
Domperidone - regular tablets can be dispersed in 10ml of water. Also available as suspension and suppository.
