Pharmacology Parkinson Disease Flashcards
Symptoms of Parkinson Disease
*Progressive disorder
*Rate of disability progression is most marked in the early years
of the disease.
*Significant disability 10-15 years after onset
*At later stages, PD patients become increasingly dependent in
their activities of daily living.
*Motor fluctuation, dyskinesias and non-motor symptoms (eg falls,
postural instability, postural hypotension, confusion, dementia, suboptimal nutrition, speech and sleep disorders) are common at later stages.
Motor symptoms of PD
1.Tremor at rest
2.Slowness of movement (bradykinesia)
3.Rigidity (stiffness and resistance)
“cogwheel-like” movements of arms
Postural instability
1/2/3 = Cardinal features of PD
Non-motor manifestations of PD
Autonomic, neuropsychiatric, olfactory and sensory
Common in PD as many as 88% of patients have at least one nonmotor symptom and 11% with five nonmotor symptoms
More prominent in later stages of PD
Relatively resistant to, and may be worsened by dopaminergic agents
Cause significant disability
Often neglected in PD management
AE of levodopa
Side effects:
– Short term: nausea, vomiting, postural hypotension
– Long term: motor fluctuations and dyskinesia (10%/yr)
– Although levodopa is the most efficacious drug for the symptomatic
management of both early and late Parkinson’s disease, the dose of
levodopa should be kept to the minimum necessary to achieve good
motor function.
*** COMT inhibitors - side effects (7)
increase abnormal movements (dyskinesias)
– liver dysfunction (Tolcapone)
– nausea, diarrhea
– urinary discoloration
– visual hallucinations
– daytime drowsiness, sleep disturbances
Example of anticholinergics
Trihexyphenidyl (Artane)
Anticholinergics advantages
Advantages:
– May be effective in controlling tremor
– Peripherally acting agents may be useful in treating
sialorrhoea
AE of anticholinergics (7)
– Side effects (especially in elderly):
– Dry mouth, sedation, constipation, urinary retention, delirium, confusion, hallucinations
Dopamine agonists - side
effects
similar to levodopa
– ‘ergot’ derivative - fibrosis
– pedal edema
– somnolence with ropinirole, pramipexole
– arrhythmia
– Pergolide - restrictive valvular heart disease
Which medication to use for PD?
Treatment has to be individualised
according to:
–age
–stage of disease
–level of activity
–associated psychological factors
–associated medical conditions
–patient factors
Early Symptomatic Disease
without complications:
May not even need oral medications if coping well
More importantly,
– Physiotherapy and exercise regime (stretching, maintain balance and posture)
– Healthy and balanced diet
– Knowledge on disease
– Social support
If oral medications required…
- Anticholinergic agents (eg Artane)
– MAO-B / COM-T inhibitors (eg
Selegiline)
–Dopamine agonists (eg Bromocriptine)
– Levodopa (eg Madopar)
Pathophysiology of PD
*Impaired clearing of abnormal/damaged intracellular
proteins by ubiquitin-proteasomal system.
Failure to clear toxic proteins
-> accumulation of aggresomes
-> apoptosis
Lewy bodies ≈ aggresome, containing α-synuclein and ubiquitin
Degeneration of dopaminergic neurons with Lewy body inclusions in substantia nigra, locus ceruleus, cortical association areas, hypothalamic neurons, sympathetic ganglia, parasympathetic neurons, olfactory bulb.
Substantia nigra has dopaminergic projections to basal ganglia
Facilitates and modulates motor movements initiated by motor
cortex
Synthesis:
-L-tyrosine
-L-dopa
-> L-dopa (tyrosine
hydroxylase)
-> dopamine (DOPA
decarboxylase)
Breakdown:
dopamine
dopamine -> homovanillic acid
(catechol-O-methytransferase,
COMT & monoamine oxidase,
MAO)
Strategies for increasing or decreasing dopamine synthesis
1) Increase dopamine synthesis
Levodopa
2) Inhibit dopamine breakdown with
COMT inhibitors
3) Strategy: inhibit dopamine breakdown with MAO-B inhibitors
Strategy: activate dopamine receptors Dopamine agonists
Strategy: Increase dopamine synthesis Levodopa
Gold Standard
- First available in 1960s
Madopar HBS, madopar 250, Sinemet 100
- Dopamine precursor, “2-in-1” preparation with peripheral
decarboxylase inhibitors to prevent side effects due to excess DA
in PNS (Eg, Levodopa + carbidopa: Sinemet)
**Although levodopa is the most efficacious drug for the symptomatic management of both early and late Parkinson’s disease, the dose of levodopa should be kept to the
minimum necessary to achieve good
motor function.
Levodopa + carbidopa:
Sinemet
Strategy: inhibit dopamine breakdown with COMT inhibitors
Entacapone (Comtan®) or Tolcapone (Tasmar®)
blocks an enzyme that converts levodopa into an inactive form
more levodopa is available to enter the brain
only effective if used with levodopa
increases duration of each dose of levodopa, beneficial in treating “wearing off” responses
Strategy: inhibit dopamine breakdown with
MAO-B inhibitors
E.g., Selegiline (Jumex®)
can be taken by itself
mild antiparkinson activity
inhibits enzyme monoamine oxidase B, interferes
with breakdown of dopamine
laboratory studies suggest that it may delay the nigral brain cell degeneration
Selegiline is efficacious as a symptomatic monotherapy and may be used in early stages of Parkinson’s disease.
EG of anticholinergic
Trihexyphenidyl (Artane)
Anticholinergic agents may be used
as symptomatic monotherapy or as
an adjunct to levodopa to treat
tremors and stiffness in Parkinson’s
disease.
Strategy: activate dopamine receptors Dopamine agonists
Used since 1970s, adjunct or monotherapy
- Available as
– Bromocriptine (Parlodel®)
– Pergolide (Celance®, Permax®)
– Piribedil (Trivastal Retard®)
– Ropinirole (Requip®)
– Pramipexole (Sifrol ®) - Act directly on dopamine receptors in the brain to reduce the symptoms
of PD - Antiparkinsonian effects not superior to levodopa (levodopa still the gold standard)
- Prevent or delay onset of motor complications
Dopamine agonists are efficacious as
symptomatic monotherapy. Dopamine agonists
may also be used as an adjunct to levodopa in the treatment of Parkinson’s disease
In younger Parkinson’s disease patients, therapy should commence first with dopamine agonists rather than levodopa.
AE of ropinirole and pramipexole
Dopamine agonist
Somnolence, strong desire for sleep/ sleeping for unusually long periods of time
AE of pergolide
restrictive valvular heart disease
