Hello Bill, A late reply to your email, but I hope it will prove useful.
I don't think that quoting a half-life for a tablet like Sinemet CR is really
appropriate.
The trem 'Half Life' has presumably been borrowed from the nuclear
science field, where it is used to describe the active life of radio-active
compounds, which tend to degrade in an exponential way. Thus, if a compound
has a half-life of 50 years it means that it will lose half its intensity in
50 years. After another 50 years the intensity will have fallen by half again, so it is now a quarter of its original intensity, and so it goes on.
The use of Half-life nomenclature is appropriate when we talk about the
Dopamine Agonists such as Bromocryptine (Parlodel) and PerMax (Celance, or
Pergolide). Both these drugs take several weeks to achieve a stable level, once
you start taking them, and likewise, if you stop taking them, it will be some
weeks before the effects go back to zero.
Sinemet CR has been designed with the objective of releasing its mix of
Levodopa/Carbidopa in such a way that to the patient, the effect remains at
a constant level for the duration of the tablet. The 'nominal' life of a CR
tablet is around 4 hours, but it can vary, depending mostly on how far down
the PD road you have travelled. I would say that the range varies from 6 hours
if you are a newly-diagnosed PWP , to 2 hours for a long-term user.
One other point may be relevant; that is the term which I see knocking around
as 'bio-availability'. I don't know where this term originated, but it is
claimed that for instance, a 200/50 Sinemet CR will only deliver about 70% of
the levodopa it contains, compared to two 100/25 non-CR tablet. All I can say
is that in my computer program (which for newcomers is designed to help
evaluate the optimum tablet strategy for anyone with PD), I find it completely
unnecessary to invoke such a factor.
If anyone out there knows, could they tell me whether the term has a
background of good science, or is it just another term dreamed up to describe
an anomalous result which could't be explained?
--
Brian Collins <[log in to unmask]>
