Subject: Carbidopa Toxicity I am re-sending this message, which originally went out on 24 November, but appears to have had some problems. Apologies if you have seen it before. Hello to you all, and thanks to Pam Barnett for her kind comments. I must apologise for not responding to any discussions over the last week. I have been up-grading my computer with a super-fast new processor, and it took a little while to teach it who was in charge. Anyway, I am back now, and would like to address some of the points made regarding Carbidopa. I do believe that too much Carbidopa can be bad for you. The story as I understand it is: 1/ The function of Carbidopa in the Sinemet tablet is to protect the Levodopa from chemical attack as it travels in the blood-stream from the lower intestine to the Brain. It first cane to my attention that there can be such a thing as too much Carbidopa when reading the excellent book by Dwight C. McGoon- 'The Parkinson's Handbook' (Published by the Norton Press of New York) - I will say a little more about this book later-. Since then I have asked several neurologists the same question, and the concensus is that only 70 to 100 mg of Carbidopa per day is required to provide effective protection to the levodopa. 2/ So: What happens to the unwanted excess carbidopa. The clever thing about Carbidopa is that it cannot get into brain, and is forcibly separated from the levodopa at the blood-brain-barrier. By this time, the Carbidopa, cast adrift after doing a fine bodyguard job on the levodopa, is probably going to have what we might call an attitude problem, so it sets off to do the one thing it is good at: protect Large Amino-Acids from chemical attack. And they are there in profusion; their reason for being there to act as the building blocks for protein in various parts of the body.They need to interact chemically to do their job, and the carbidopa will spoil this delicate balance, until it is eventually broken down by the liver. The theory ( Idon't think it can be called more than that) is that by interfering with the delicate balance in the blood stream, the Carbidopa produces feelings of lethargy, sleepiness, lassitude, etc. 3/ If the above argument is unconvincing to a sceptical neurologist or doctor, you might ask why else do Sinemet produce a specially low dose tablet having 100 mh of levodopa and only 10 mg of Carbidopa. 4/ This next point may be a complete red-herring, but I just put it forward as a possibility. A friend of mine living in Derby is, as far as I know, the record holder for levlodopa usage: taking an average of 3000 mg of levodopa per day. - That's right: Three Thousand milli grammes per day. (And of course 750 mg of Carbidopa ). I remembered him describing symptoms very like those listed above, and before writing this email, I phoned to check his status. When I listed the symptoms he immediately agreed that they were a perfect description of his condition, but then said that he no longer has the problem, since he switched to Madopar! ( For the benefit of USA residents, I should explain that Madopar is available in many countries as an alternative to Sinemet, and it functions interchangeably with Sinemet in normal useage.) Where Sinemet contains levodopa and carbidopa, Madopar contains levodopa and Benserazide. I don't know enough chemistry to have a clue as to whether this is significant, but it does make you wonder. To return to Dr. McGoon's book. The first 50 or so pages contain by far the most clearly-written and jargon-free description of how the parts of the brain which are associated with PD work, and I would recommend it to anyone. However, when he gets on to the 'Drug Holiday' idea, I switch off! I have occasionally (for quite unrelated reasons) found it necessary to go without my tablets for a day, and I would say that the relief when the first dose of levodopa cut in after that ordeal was great (in comparison with the preceeding 24 hours). but I don't think it went beyond that. I do recognise however that perhaps the point at which I am in the long decline that we call PD may be different to Dr. McGoon's point. We all tend to see things as they affect us personally, and Parkinson's being what it is, with the variety of effects being almost as numerous as the number of sufferers, I may yet find myself agreeing with the idea of a 'drug holiday' I would be interested tp hear from anyone with experience of both Madopar and Sinemet, especially if one or the other produced different reactions in the patient. Regards -- Brian Collins <[log in to unmask]>