>>> Posting number 37457 Date: Wed, 11 Feb 1998 12:36:45 -0500 From: Stephan Schwartz Subject: Carbidopa/levodopa ratio Arthur wrote: >>>One also wonders why the carbidopa/levodopa ratio is the same in both pill sizes: would we not expect the carbidopa requirement to remain constant as the levodopa requirement rises?<<< Art 62/12<<< Hello Arthur: To my knowledge there are three carbidopa/levodopa ratios in regular release Sinemet - 10/100, 25/100 & 25/250. For timed-release Sinemet (CR) there are two dosages - 25/100 & 50/200. So for regular Sinemet the carbidopa/levodopa ratio fluctuates from 1 to 10, then 1 to 4, and then 1 to 10 again. For Sinemet CR the ratio is a constant 1 to 4. To complicate matters even more the ratio in regular and timed release Madopar (benesarizide/levodopa) is a constant 1 to 4 for both preparations: Madopar'62.5' =12.5b/50l Madopar'125' = 25b/100l Madopar'250' = 50b/200l &Madopar HBS = 25b/100l [timed release] Now, your question: Why doesn't the amount of carbidopa remain constant despite the rise in the amount of levodopa in each pill? There is a highly specialized area of the brain at the junction with the spinal cord called the vomiting center (medical term?). There, nerve cells detect toxins in blood circulation and provoke vomiting to prevent further absorption of the poison by expelling the matter from the stomach. The vomit center is sensitized to levodopa, in varying degrees for patients, according to their individuality. In some patients the vomit center can become desensitized to levodopa over a period of time. Therefore, in some patients the action of carbidopa as an inhibitor is not uniform. Researchers estimate that the optimum daily level of carbidopa in the bloodstream is approximately 75mg . . . below that, some patients still experience nausea. However, because of the differences among patients, that estimated level could be less or more in practice. Hence, the amount of carbidopa in the regular release pill 10/100, even taken at several intervals throughout the day, may not be sufficient over a 24 hour period for that patient to avoid the formation of some levodopa in the bloodstream that triggers the vomit center. The pills are purposely scored to allow the patient to adjust the levels of carbidopa and levodopa by adding some carbidopa during the day [breaking a 25/100 to take half - 12.5/50] thereby getting just enough extra carbidopa [12.5mg] to inhibit nausea, but not too much additional levodopa [50mg] that could trigger dyskinesias. Stephan 53/7 anyone can retrieve any message from the PARKINSN list archives as easy as: 1. send the following e-mail message (where xxxxxx = the post numbers): GETPOST PARKINSN xxxxxx xxxxxx xxxxxx 2. to the PARKINSN listserver at: [log in to unmask] 3. and, bob's yer uncle, the listserver will e-mail them to you in minutes! janet paterson ~ [log in to unmask] ~ http://www.geocities.com/janet313/ ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn