This is chapter five neuro, and in this video, we'll be discussing Parkinson and Alzheimer's disease.
We'll start with Parkinson's disease, and this is a disorder that is associated with motor symptoms.
When we think of people who have Parkinson's, we often think of celebrities - a celebrity would be Michael J Fox.
Parkinson's is caused by the loss of dopamine receptors in the brain which can lead to
decreased dopamine, so the way that we treat it is by
increasing the amount of dopamine available in the brain. The first medication we'll discuss today is a combination medicine of
levodopa and carbidopa and the brand name is Sinemet. This medication
basically just replaces our dopamine. Levodopa works by increasing dopamine synthesis,
and this is one of the most effective drugs that we have currently to treat Parkinson's. The carbidopa actually has no effect on
the Parkinson's itself, but it just makes levodopa more available to the brain. Levodopa
can get into the brain, but it can also circulate in the vasculature, so by preventing it from
being
degraded, we can make it more available to the brain and then we can also give smaller doses to avoid some side effects.
You can remember that these deal with
Parkinson's disease because they both end in -dopa and we need to increase the dopamine to treat Parkinson's.
The second medication is selegiline or the brand name
Eldepryl. The way that selegiline works is that it inhibits monoamine oxidase
B receptors. As you recall from the antidepressant video,
we use monoamine oxidase inhibitors in depression because monoamine oxidase breaks down different
neurotransmitters in the brain,
so
when we are selecting for the B, receptor with a monoamine oxidase B
inhibitor, that prevents dopamine from being metabolized and
this is thought to be neuroprotective,
which just means that it's thought to maybe delay or prevent the neural progression in the brain of Parkinson disease.
We can remember that -giline, the stem of selegiline, means Parkinson's and then we can also remember that Eldepryl
sounds kind of like Elderly, and that's who we mostly see Parkinson's in.
Next we're going to discuss a couple different therapies for Alzheimer's disease. Alzheimer's disease is basically
categorized as memory loss and having impairments in thinking.
The reason that Alzheimer's happens, they think, is because of the loss of acetylcholine in the brain,
wo we're going to try to increase levels of acetylcholine to treat it. The first medication
we'll discuss today is donepezil, the brand name is Aricept. That is a cholinesterase inhibitor.
Acetylcholine is typically broken down by an enzyme called acetylcholinesterase.
If we give an acetylcholinesterase inhibitor, that will inhibit the enzyme that breaks down acetylcholine,
Leading to increases in acetylcholine,
leading to
symptomatic benefit.
We can remember that donepezil is for Alzheimer's because we can
remember 'don't remember zilch', so kind of sounds like donepezil.
The next medication we'll discuss for alzheimer's is memantine, the brand name is Namenda.
Memantine is an NMDA receptor
antagonist. NMDA receptors are involved in memory and learning,
so we think that in Alzheimer's, there's an overstimulation
of glutamate on those receptors, so if we block glutamate, we can protect against further damage. A way to
remember that memantine is for Namenda
the 'mem-' in memantine we can remember that it sounds like memory and
then for Namenda we can think of Namenda as 'mending the brain'. Namenda also has an
NMDA in it and that's just like the receptor, so then we can remember the mechanism action as well.
Let's go through a few questions.
Practice question 1- 'A combination
medication used to treat Parkinson's disease that contains a drug that enhances the effect of the other drug is?'
Like we said before, we have our four medications that we are going to discuss today.
The correct answer is levodopa / carbidopa.
This is the only medication with two drugs,
so that's why B), C) and D) are incorrect. As you recall, levodopa
increases dopamine synthesis and then carbidopa just makes more levodopa available to the brain.
Now we'll go over
answers B) C) and D) and we'll change the question so that we can make B) C) and D) correct.
So practice question three 'An MAO B
Inhibitor that is thought to be neuroprotective in Parkinson's disease is?' The answer is B)
selegiline because B) is an MAO B
inhibitor and it is neuroprotective, which means it might just delay disease progression and
degeneration in the brain. A) is incorrect because it is for Parkinson's
but it has a different mechanism of action
and it's not neuroprotective. C) and D) are incorrect because those are agents that we use to treat Alzheimer's disease.
Question 4 - 'Which of the following medications is an acetylcholinesterase
inhibitor?' The correct answer is C) donepezil. As you can recall with
Alzheimer's disease, we want to increase the amount of acetylcholine.
Acetylcholine is broken down by acetylcholinesterase,
so if we give an acetylcholinesterase
inhibitor, we will prevent the breakdown of acetylcholine and then increase the levels in the brain.
D) memantine is incorrect because it is an NMDA receptor
antagonist, and A) and B) are incorrect because of their mechanisms as well as they are used for Parkinson's and not Alzheimer's.
Practice question 5 - 'An NMDA Receptor
antagonist that is indicated in moderate to severe Alzheimer's disease?' and the answer is D) memantine,
it is the NMDA receptor. As we recall that the brand name Namenda
contains an N, M, D and A and this is just in the indicated for moderate to severe Alzheimer's.
A) and B) are incorrect because of their mechanisms of action and also their use for Parkinson's and not Alzheimer's,
and donepezil is incorrect because the mechanism of action is different,
and we actually used in donepezil earlier on in Alzheimer's treatment.
It is also indicated for mild Alzheimer's unlike memantine.