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Parkinsonian Links
Pharmacology
How Parkinson drugs work:
There are four principal categories of ways in which medications can affect
the symptoms of Parkinson's disease:
1. The medication can deliver more dopamine to the brain and to the body
to replace the dopamine which is no longer being manufactured by the brain
cells. The use of levodopa is the gold standard here. But, because
levodopa can be metabolized in parts of the body where it will have no good (i.e. adverse effects)
effect, it is necessary to protect it until is passes through the blood
brain barrier.
Medication must be taken inhibit the metabolism of the levodopa where it is
not needed. A dopa-decarboxylase inhibitor, such as carbidopa or
benserazide, is included with the levodopa to minimize metabolization of
the levodopa where it will have (adverse) no effects. Typical medications of
levodopa and these inhibitors bear the trade names Sinemet, Prolopa, and Madopar.
COMT (catechol-o-methyl transferase) is another enzyme that can block metabolism of levodopa where it is of no use. Entacapone is a COMT inhibitor. It is available with the trade name Comtan, or combined with levodopa and carbidopa with the trade name Stalevo.
2. Dopamine agonists work by stimulating dopamine receptors, so not as much dopamine is needed. Typical product names include Parlodel (bromocriptine), Permax (pergolide), Mirapex (pramipexole), and Requip (ropinerole). The choice of which agonist to use, if any, is highly dependent upon how the body responds to the various agonists. Mirapex and Requip appear to be safer and better tolerated in general.
3. In the brain, Dopamine is a transporter of information (i.e. an exitatory neurotransmitter), but there is also acetyl-choline (an inhibitory neurotransmitter), which impedes the flow of information. By inhibiting
the effect of the acetyl-choline, it is possible, within a limited range,
to restore the Cholenergic/Dopaminergeic balance. Various
anti-cholingerics are used for this purpose (e.g. benztropine, trihexyphenydyl)) .
4. Other medications work, but we know not
why. Amantadine, brand name Symmetryl, is one such example. Originally
intended as an anti-viral for influenza, Parkinsonian patients observed a lessening of their
symptoms when they were taking it. It has become a medication often
prescribed, primarily in early cases, because it is effective for a while
and it postpones the need for a more sophisticated regimen (i.e. levodopa).
Selegeline, brand names Eldepryl and Deprenyl, is another medication often
prescribed for Parkinson's. Originally it was thought to slow the
progression of the disease, but many in the medical profession doubt the
validity of this. Another view is that because it is a mono-amine oxidase
inhibitor type B (MAO-B), this medication inhibits the breakdown of
dopamine. Whatever the mechanism, it has proved effective in some patients.
There are side-effects, both positive and negative, when one tries to
combine medicines with one another, with over-the-counter medications, and
even with vitamins and minerals. One should consult with one's doctor or Pharmacist
before changing one's medications - adding, deleting, or changing in
quantity or timing. A good doctor will understand that your requirements
are not the same as everybody else's, and (s)he will give you guidelines
for making changes.
Your pharmacist specializes in knowledge about drugs, interactions and side
effects, and should be consulted as well. Make certain that your
pharmacist knows about all of the medications that you take. Don't be
hesitant to tell your pharmacist about medications that you buy elsewhere,
as only then can (s)he apply the full range of knowledge about medications
that is available. It is best to use one pharmacy only, for both prescription and OTC medications.
Your reading of information on the Web may alert you to both potential
problems and potentially useful ideas for your Parkinson's situation. But
before you put yourself to risk, contact your physician and your
pharmacist. Keep alert for good questions, and don't be satisfied with
half an answer. The news about a bad interaction may reach you before your
doctor knows about it. Neuroleptic Malignant Syndrome (NMS)
also involves your medications and is something that may not occur to your
doctor if you don't ask about it.
Finally remember that medications are dispensed also by dentists and
anesthetists. Foods can also interact with medications, but that is a specialty
unto itself.
Thanks to Rick Nemett, B.Sc. Phm., CGP, of Shoppers Drug Mart for his help in writing the above.
Murray Charters has gathered a list of hyperlinks regarding pharmacology.
Return to Links Page, "Medications"
E-mail me with comments at
epr@airmail.net. | It is a sad fact that every web page
like this must add "Disclaimers apply." Revised 27 May, 2004 |  | |
