Kathrynne Holden and others interested,

I request that you browse and copy as you wish - the medication and
pharmacokinetics "primer taste" sub-pages in the PD section that reside
on my home page (URL is bottom line of signature at end of message.).

I believe that some aspects of the "half-life" concept might benefit
your understanding of the metabolic reactions that convert levodopa into
no-longer-usable chemicals are concentration and rate (time) dependent.
The individual levodopa molecules are not losing their potency with
passage of time.  There are just fewer of them left in the system.

If they are in the stomach (longest with fats in large chunks of red
meat) longer, the amount available when transported to the duodenum and
small intestine will be much less than if not held there.

The digestive juices are not going to secrete if only the pill is there
and the stomach is empty, so some food soon after the pill (or orange
juice with it) will give the two effects of transporting the med with
digestive material into the intestine where the large neutral amino acid
(LNAA) "transporters" are activated to bring the amino acids (levodopa
is carried by these transporters) into the bloodstream. (I conjecture
that the antacids taken with levodopa may stimulate digestive juices
flow and transport that helps some get best results.)

The graphical addition method is very common chemical engineering
technique that is pertinent. Bob Naylor's usage of it with his "typical"
blood plasma concentration measured data was the basis of what I did. I
did get more data from the "Pharmacokinetics and bioavailability of
Sinemet CR: A summary of human studies", NEUROLOGY 1989:39(suppl
2):25-38.

The CR medication is differently affected by food interactions - because
it is made with binder such that the dissolving is slow rather than
rapid. This effect is beneficial in retarding the rate of dissolving
which reduces the initial peak concentration of levodopa in the blood
plasma and makes the dissolving the rate-determining factor (rather than
the metabolic reactions half-life). However, these benefits are gained
at the expense of reduced efficiency in that only 70 to 75% of the
levodopa in the pill on average ever gets into the bloodstream versus
over 99% from the regular medication.  Also, the variability of
absorption into the blood in amount over time is extremely large. (You
might recall that several constipated persons had whole or near whole CR
tablets in the fecal matter removed surgically - or eventually passed
via enema.)

Another factor that may cause difficulty with CR is several delayed
doses being absorbed at once if bowel movement or exercise gets the
chyme mass moving after inactivity.

I also believe that several anecdotal instances have noted improvement
from taking regular medication in instances where more than 300
milligrams of carbidopa per day were being taken.  The CR tablets all
have 25/100 ratio carbidopa while the 10/100 and 25/250 regular tablets
are available to allow getting the recommended 75 mg. per day. I have
not found any data or indication that this potential overdose of
carbidopa problem was investigated.  There could be such concentration
of carbidopa in the blood that it crosses the blood-brain-barrier - or
some other adverse effect(s) might be caused in the peripheral systems.

--
ron      1936, dz PD 1984  Ridgecrest, California
Ronald F. Vetter <[log in to unmask]>
http://www.ridgecrest.ca.us/~rfvetter