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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