Arthur wrote:
>>> Arthur Hirsch <[log in to unmask]> 02/11/98 10:43am
>>>One also wonders why the carbidopa/levodopa ratio is
the same in both pill sizes: would we not expect the
carbidopa requirement to remain constant as the levodopa
requirement rises?<<<
Art 62/12<<<
Hello Arthur:
To my knowledge there are three carbidopa/levodopa
ratios in regular release Sinemet - 10/100, 25/100 & 25/250.
For timed-release Sinemet (CR) there are two dosages -
25/100 & 50/200.
So for regular Sinemet the carbidopa/levodopa ratio
fluctuates from 1 to 10, then 1 to 4, and then 1 to 10 again.
For Sinemet CR the ratio is a constant 1 to 4. To complicate
matters even more the ratio in regular and timed release
Madopar (benesarizide/levodopa) is a constant 1 to 4 for both
preparations: Madopar'62.5' =12.5b/50l
Madopar'125' = 25b/100l
Madopar'250' = 50b/200l
&Madopar HBS = 25b/100l [timed release]
Now, your question: Why doesn't the amount of
carbidopa remain constant despite the rise in the amount of
levodopa in each pill?
There is a highly specialized area of the brain at the
junction with the spinal cord called the vomiting center
(medical term?). There, nerve cells detect toxins in blood
circulation and provoke vomiting to prevent further absorption
of the poison by expelling the matter from the stomach.
The vomit center is sensitized to levodopa, in varying
degrees for patients, according to their individuality. In some
patients the vomit center can become desensitized to
levodopa over a period of time. Therefore, in some patients
the action of carbidopa as an inhibitor is not uniform.
Researchers estimate that the optimum daily level of
carbidopa in the bloodstream is approximately 75mg . . .
below that, some patients still experience nausea. However,
because of the differences among patients, that estimated
level could be less or more in practice.
Hence, the amount of carbidopa in the regular release pill
10/100, even taken at several intervals throughout the day,
may not be sufficient over a 24 hour period for that patient to
avoid the formation of some levodopa in the bloodstream that
triggers the vomit center. The pills are purposely scored to
allow the patient to adjust the levels of carbidopa and
levodopa by adding some carbidopa during the day [breaking
a 25/100 to take half - 12.5/50] thereby getting just enough
extra carbidopa [12.5mg] to inhibit nausea, but not too much
additional levodopa [50mg] that could trigger dyskinesias.
Stephan 53/7
