PARKINSON'S: LEVODOPA

Question 1

Dopamine pathway

Answer 1

• Dopamine is unable to cross the BBB
• It is important to note that levodopa can be metabolised on either side of the BBB
• 90% of levodopa gets converted into dopamine in the intestinal wall by DDC
  o So it is administered with a DDCI
• SUCH AS carbidopa or benserazide in order to prevent metabolism until after it has crossed BBB
• 5% of levodopa is metabolised by plasma COMT
  o COMT inhibitor
  o Entacapone may be used as an adjunct

Question 2

What is levodopa given in combination with?

Answer 2

dopa-carboxylase inhibitor
* e.g. Benserazide or Carbidopa

Question 3

Levodopa side effects

Answer 3

• Postual Hypotension
• N+V
• Hallucinations
• Response fluctuation
• Impulse disorders
• Sudden onset of sleep
• Red urine
• Motor complication
• Dyskinesia

himrsprn

Question 4

Response fluctutations

Answer 4

Response of motor function can vary at
certain times
* During “ON” period, normal
function is present
* During “Off” period, weakness and restricted mobility occur (dyskinesia and dystonia)
Shortening the interval between drug doses or using combinations may help

Question 5

What does “End-of-dose deterioration” mean with regard to levodopa?

Answer 5

• Levodopa gives a shorter duration of benefit progressively
• As disease getting progressively worse
• akinesia and rigidity
• MR preps may help

Question 6

Akinesia

Answer 6

• abnormal movement
• hard to move e.g. swing arm (can be used interchangeably with bradykinesia which means slowness of movement)

Question 7

Impulse disorders

Answer 7

o Pathological gambling
o Binge eating
o Hypersexuality

Question 8

How is sudden onset of sleep treated?

Answer 8

modafinil - review every 12 months
o DVLA needs to be informed, pt advised not to drive

Question 9

How is nocturnal akinesia treated?

Answer 9

1. Levodopa
2. Dopamine-receptor agonist e.g. Rotigotine

Question 10

How is postural hypotension treated?

Answer 10

1. Midrodine
2. Fludrocortisone