Pharmacotherapy for Movement Disorders Flashcards
under normal conditions the SNc favors the which pathway?
direct pathway
in PD the activity of which pathway predominates?
indirect pathway
___________ receptor activation appears to be most important in gating the balance of the direct and indirect pathways
D2
what are the 5 main strategies for PD pharmacotherapy?
- replace DA
- Stimulate DA receptors
- Enhance DA release
- Inhibit DA metabolism
- Alter DA/ACh
which drug is the single most effective treatment for PD?
L-DOPA
Which drug can completely ameliorate all the symptoms of PD, particularly during initial treatment?
L-DOPA
what is the MOA of L-DOPA?
replenishes DA Stores in the remaining DA terminals in the striatum
L-DOPA is converted in the periphery and brain to dopamine by what enzyme?
L-aromatic aminoacid decarboxylase (L-AAD)
99% of systemically administered L-DOPA is converted to dopamine in the periphery, and is principally excreted in the urine as what two substances?
HVA & DOPAC
L-DOPA has to be co-administered w/ what drug?
carbidopa
what is the MOA of cabidopa?
inhibits L-aromatic amino acid decarboxylase (L-AAD)
-prevents metabolism of L-DOPA to dopamine in the periphery (you want L-DOPA to remain unchanged so it can cross the BBB)
what are the two main benefits of using carbidopa with L-DOPA?
reduces the amount of L-DOPA needed by up to 75% & reduces side effects due to reduced level of peripheral DA
the GI and CV adverse effects of L-DOPA are due to what?
due to the response to L-DOPA monotherapy
what are the GI adverse effects of L-DOPA monotherapy?
anorexia, N/V, tend to decrease w/ repeated use
what are the CV adverse effects of L-DOPA monotherapy?
arrhythmias, tachycardia, ventricular extrasystoles, Afib, incidence tends to be low except in those predisposed, also orthostatic hypotension
the behavioral and dyskinesias are adverse effects of L-DOPA therapy with what other drug?
carbidopa
what are the behavioral adverse effects of L-DOPA combo therapy w/ carbidopa?
depression, anxiety, delusion, agitation, insomnia, hallucinations, nightmares, euphoria. (antipsychotics are used to alleviate this problem)
what are the dyskinesias associated with L-DOPA combo therapy with carbidopa?
chorea, myoclonus, tics, tremor
the adverse effects for which drug have fluctuations in response like a “on-off phenomenon”?
L-DOPA
what is the main drug interaction with L-DOPA, that causes an increase in L-DOPA metabolism?
vitamin B6 (pyridoxine)
why is it not ok to give L-DOPA to pts on MAO-A inhibitors?
hypertensive crisis
what are some of the contrindications for L-DOPA therapy?
psychotic pts, glaucoma (angle-closure), cardiac disease, peptic ulcer, melanoma
Therapy with L-DOPA is often effective for how many years?
3-5 yrs (often delayed until symptoms of PD yield functional impairment)
What is the rationale behind dopamine agonist therapy?
to activate D2 receptors to reduce the activation of the indirect pathway?
what are the advantages to dopamine agonist therapy?
- doesn’t have to be converted to active compound
- no toxic metabolites
- doesn’t compete w/ other substances for GI absorption or crossing BBB
- may be more selective (reducing adverse effects)
what kind of drugs are considered the preferred therapeutic strategy for early PD?
dopamine agonists
which kind of drugs may be used in combo w/ L-DOPA in advanced PD to reduce the “on-off” phenomenon?
dopamine agonists
name the drug: D2 agonist/D1 partial agonist
bromocriptine
name the drug: D1/D2 agonist
apomorphine
name the drug: D2 selective, may also act as a free radical scavenger
pramipexole
name the drug: D2 selective, metabolized by CYP1A2
Ropinirole
which drug is an antiviral agent that was found to alleviate parkinsonian symptoms?
Amantadine
how long do the effects of amantadine last?
effects are modest and short-lived
how is amantadine excreted?
urine
what are the adverse effects of amantadine?
restlessness depression agitation irritability insomnia excitement hallucinations confusion overdose may produce psychosis other adverse effects similar to L-DOPA and dopamine agonists
which drug is contraindicated in pts w/ history of seizures or heart failure?
amantadine
which drug is a selective MAO-B inhibitor that retards the breakdown of dopamine?
Selegiline
metabolites of selegiline include what two drugs that increase dopamine release?
amphetamine & methamphetamine
what is the indication for selegiline?
used primarily in pts whose responsiveness to L-DOPA has declined (little effect when administered alone)
what are some of the drug interactions of selegiline?
don’t take w/ meperidine, TCAs, or SSRIs
what are the adverse effects of selegiline?
May potentiate the adverse effect of L-DOPA
name the drug: a new more potent inhibitor of MAO-B approved for combo therapy w/ levodopa in late-stage or alone in early PD?
rasagiline
name the two drugs that are selective inhibitors of COMT?
entacapone, tolcapone
what is the MOA of entacapone and tolcapone?
prolongs the action of L-DOPA, reduces the production of 3OMD which may compete w/ L-DOPA for transport carriers in GI and BBB
-increases the bioavailability of L-DOPA
What is the indication for enacapone, tolcapone?
helpful in reducing fluctuation responses to L-DOPA
name the inhibitors of DA metabolism that are both rapidly absorbed, highly bound to protein, half-life about 2 hrs?
entacapone, tolcapone
which COMT inhibitor has both central and peripheral effects?
tolcapone
which COMT inhibitor has only peripheral effects?
entacapone
which COMT inhibitor is preferred b/c the other one may result in increased liver enzymes and hepatic failure (requires pt consent)
entacapone is preferred
tolcapone (causes increased liver enzymes and hepatic failure, requires pt consent)
what are the muscarinic antagonists used to block cholinergic activation in the striatum (3)
benztropine
diphenhydramine
trihexyphenidyl
what are the adverse effects of the muscarinic antagonists used to treat PD?
drowsiness, mental slowness, inattention, confusion, delusions, hallucinations, and mood changes
using muscarinic antagonists to treat PD are contraindicated in pts with what conditions?
prostatic hyperplasia
OBD
glaucoma
(avoid concomitant use of drugs with antimuscarinic effects-like TCAs or antihistamines)
what is the trinucleotide repeat found in huntington’s?
CAG (glutamine, polyglutamine expansion)
the huntingtin gene is located on what chromosome?
4
Huntington’s disease has a loss of cholinergic neurons in the striatum but a greater and earlier loss is observed in WHICH NEURONS that project to the external globus pallidus (indirect pathway) thus decreasing the output (STN) of the indirect pathway?
loss is observed in the striatal medium spiny GABAergic neurons which project to GPe
what are the 2 main drugs used to treat HD associated depression?
Fluoxetine
carbamazepine
what are the central dopamine depleting agents drugs used to treat HD associated chorea?
reserpine and tetrabenazine
what are teh dopamine antagonists that are used to treat HD associated chorea?
chlorpromazine and haloperidol
what is the proposed MOA of the drugs used to treat HD associated chorea?
thought to be able to block D2 receptors