I think it fairly likely that the Dopamine level decay decreases exponentially
not to zero but to a baseline level.This level is the residual production by the
body of its natural dopamine. This would give the baseline level that Joe talks
about. Other medications concentration such as mirapex would decay to zero
because these are not natural (made by the human body) substances.
K-F Etzold (cg Carline)
"J. R. Bruman" <[log in to unmask]>@listserv.utoronto.ca> on 09/15/99 01:08:01
PM
Please respond to "Parkinson's Information Exchange"
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Subject: Half-life of medication
The replies in the recent postings may be strictly accurate, but I think
perhaps in some cases the problem may be more complicated. In
particular, the concentration of levodopa (as in Sinemet) in the blood
may be measured as a function of time, but the concentration of
dopamine produced from levodopa, within the brain, is not so easy to
measure. First, the concept of a half-life implies the *assumption*
that the decay in question follows a specific mathematical law. Second,
I've felt for some time (and I think some experts agree) that the amount
of dopamine in the brain has two components: There is a long-term, or
"baseline" part that is independent of medication and reflects only the
progression of PD; then there is the part that is *added* by taking
levodopa as medication. I think it is only this second part that obeys
the "half-life" rule of decay. Instead of that number, what I'd like to
see is something that indicates how much of any given pill you need to
take, in order to maintain a desired baseline level (that is, the level
you would find in a subject without PD symptoms). Cheers,
Joe
--
J. R. Bruman (818) 789-3694
3527 Cody Road
Sherman Oaks, CA 91403-5013
