Camilla Flintermann wrote: <<We've been trying to get a med routine that will help Peter with the awful lethargy he experiences at many times through the day. About 6 weeks ago the neuro put him on 6XSin>CR 50/200 at 4 hour intervals around the clock--no improvement. Today I went armed with info from this list re: CARBIDOPA, and when I suggested that 300mg x day was too much, he agreed, said "that's what I might have said myself" (but of course he DIDn't say it first) and agreed to move P. off the CRs and try 25/250mg Sinemet instead. He suggested starting with 4 x day, but said we could go to 5 or 6 if needed, and still be at 1/2 the carbidopa P. gets now. To my question about toxicity, a point Alan Bonander made on the list, he shrugged, and said there's no evidence of that, it's just that you don't*need*more than 70-100mg carbidopa. This leads me to ask if anyone has evidence to cite about toxicity? Or is it one of those "possible" things we so often encounter with PD?>> Brian Collins sent Pat Martin's words about the non-specificity of carbidopa, so I will not repeat that. I will include portions of the following: Dietary Factors in the Management of Parkinson's Disease P.A. Kempster, M.D., M.R.C.P. (U.K.), F.R.A.C.P. and M. L. Wahlqvist, M.D., F.R.A.C.P. Dr. Kempster is with the Departments of Neurosciences and Medicine and Dr. Wahlqvist is with the Department of Medicine. Monash Medical Centre, 246 Clayton Rd., Clayton 3168. Melbourne. Australia. ABSTRACT Oral administration of L-dopa is currently the most effective way to treat the cerebral dopamine deficiency which causes Parkinson's disease. Unfortunately, many patients with advanced Parkinson's disease develop an unstable pattern of response to L-dopa because of fluctuating delivery of the drug to the brain. Diet contributes to this problem through Its adverse effects on L-dopa pharmacokinetics. This article reviews dietary strategies to improve responsiveness to pharmaceutical L-dopa treatment and the potential use of food as a source of L-dopa. Nutritional factors concerning weight loss and energy balance in Parkinson's disease are also discussed. A set of dietary guidelines is developed to assist clinical nutritionists and neurologists in the practical management of patients with Parkinson's disease. Nutrition Reviews 1994;52,2:51-58 Feb 1994 L-Dopa medication is now usually initiated in patients with relatively mild Parkinson's disease early in the course of the illness. Modern treatment combines L-dopa with a peripheral decarboxylase enzyme inhibitor (carbidopa or benserazide) to minimize conversion of L-dopa to dopamine outside the nervous system. In most cases, motor symptoms improve and a stable and satisfactory response continues for the next few years. With further disease progression, many patients begin to experience fluctuation of response to L-dopa, and drug-induced dyskinetic involuntary movements may then accompany the beneficial effects of the medication. Significant motor fluctuations develop at a rate of about l0% per treatment year.[4] In their most severe form, motor fluctuations produce, the "on-off" syndrome.[5] Patients with this affliction swing between severe Parkinsonian disability ("off' phases) and relative improvement of motor fluctuation which restores mobility at the expense of involuntary movements ("on" phases). Capricious and abrupt fluctuation between these states occurs many times a day. The fact that patients cannot predict when sudden loss of independent mobility will occur is in itself a major cause of disability in this syndrome. The pharmacokinetic properties of L-dopa lead to fluctuating blood levels, generating fluctuation of motor function in susceptible patients.[6] The drug has a relatively short half-life because of enzymic catabolism; and dietary intake is apt to interfere with its absorption and transport within the body. Fluctuating delivery of L-dopa to the brain does not seem to matter early in the disease course. However, disease progression brings increasing dependence on pharmacological dopamine receptor stimulation. Severe motor fluctuations are generally seen in patients who retain a capacity to respond well to L-dopa but have lost most of their endogenous dopamine production because of nigral cell loss. A precipitous decline in motor functions thus occurs each time that the supply of exogenous L-dopa to the brain lapses. Table 1. Dietary Factors Which Affect Clinical Response to L-Dopa Medication 1. Timing of L-dopa doses in relation to mealtime. 2. Effects of food on gastric emptying Energy content of food Meal size Food viscosity 3. Competition between dietary neutral amino acids and L-dopa for absorption across the intestinal mucosa. 4. Competition between circulating neutral amino acids and L-dopa for active transport across the blood-brain barrier. DIETARY INFLUENCES ON L-DOPA PHARMOCOKINETICS L-Dopa is normally present as an intermediate metabolite in neurons which produce catecholamine neurotransmitters (dopamine, noradrenaline, adrenaline). It is synthesized by the enzyme tyrosine hydroxylase from the diet-derived aromatic amino acid tyrosine. Brain tyrosine hydroxylase is confined to dopaminergic and noradrenergic neurons, has a high affinity for its substrate tyrosine, and its activity is regulated by the rate of neuronal firing.[9,10] Administration of tyrosine to Parkinsonian patients may increase dopamine synthesis and turnover in the central nervous system,[11] but there is no evidence of any clinical benefit from treatment with tyrosine. Phenylalanine is an indirect amino acid precursor of L-dopa but has no clinical effect on Parkinsonism.[12] A normal diet contains little L-dopa.[13] and the small amount of circulating L-dopa in normal subjects probably emanates from synthetic activity in peripheral sympathetic neurons and the adrenal medulla.[14] To exert its action In Parkinson's disease, L-dopa must he absorbed from the gastrointestinal tract into the bloodstream, cross the blood-brain barrier, and then be enzymatically converted to dopamine within the brain to interact with striatal dopamine receptors. Intake of food, particularly protein, can interfere with this process at a number of levels. Single oral doses of L-dopa, when administered in the fasting state, produce efficient and reliable absorption of L-dopa, which corresponds to predictable and relatively prolonged motor responses even in patients with the most erratic pattern of response to their usual oral L-dopa medication.[15] Patients are often advised to take L-dopa doses with meals. By reducing L-dopa absorption, food may reduce side effects such as nausea on first exposure to medication containing L-dopa. However once motor fluctuations have developed after prolonged treatment, food is usually a hindrance to the bioavailability and clinical effectiveness of L-dopa. L-Dopa is optimally absorbed from the duodenum and proximal jejunum.[16] The drug is not absorbed across gastric mucosa,[17] but oral doses are dependent on gastric emptying for access to absorption sites. The rate of gastric emptying is chiefly determined by the energy content of food and is inversely proportional to the energy density of meal.[18] Thus fat will retard gastric emptying to greater degree than either protein or carbohydrate. Low gastric acidity slows emptying [19] although routine administration of antacids to Parkinsonian patients does not improve L-dopa absorption.[20] Some types of dietary fiber increase food viscosity and slow gastric emptying.[21] The gastric mucosa contains the enzyme dopa decarboxylase,[22] which will catalyze unwanted conversion of L-dopa to dopamine, reducing the amount of L-dopa available for subsequent absorption from doses affected by delayed gastric emptying. When L-dopa is administered by naso-duodenal tube[23] or to subjects who have previously had a gastrectomy,[19] absorption is very rapid and efficient. Effects on gastric emptying are probably largely responsible for the observation that when L-dopa is given with food, the rise in plasma concentration is reduced, delayed and unpredictable as compared with fasting.[24,25] On reaching the proximal small gut, L-dopa crosses the mucosal barrier by a stereospecific, saturable active transport mechanism shared by large neutral amino acids such as phenylalanine, tyrosine, tryptophan, leucine, isoleucine, valine, methionine, and histidine.[26] Dietary protein can thus lead to competition for these active carrier sites. Once L-dopa molecules have reached the bloodstream, access to the brain is dependent on similar active amino acid transport across the blood-brain barrier for which it must compete with other circulating neutral amino acids.[27] Intravenous infusion of L-dopa at a constant rate can produce stable and sustained motor responses in patients with motor fluctuations. When oral protein or neutral amino acid loads are then administered, a transient loss of response occurs without change in blood L-dopa concentration, indicating a block to L-dopa passage into the brain through competition for transport across the blood-brain barrier.[24] Constant rate intraduodenal infusion also produces efficient L-dopa absorption, stable L-dopa blood level, and sustained clinical responses in fasting patients. With oral administration of protein, the relative importance of competition by dietary neutral amino acids at gut and blood-brain barrier levels can be compared. Oral protein causes a loss of clinical response to L-dopa without affecting blood concentration: this indicates that the major site of interference between L-dopa and amino acid active transport is at the blood-brain barrier.[28] Experimental data regarding the equilibrium constant for active transport of large neutral amino acids also agree with this observation. In gut, as in most tissues, the equilibrium constant is considerably higher than physiological concentrations of neutral amino acids. However, the constant for brain capillary endothelial cells (which form the physiological blood-brain-barrier) is about 10 times less than for other tissues and approaches the sum of postprandial plasma concentrations of large neutral amino acids.[29] Unpredictability is a major feature of severe motor fluctuations. Although patients experience the fluctuations every day, the timing of dramatic changes in motor disability and the amount of "on" and "off" time per day are never the same despite constant pharmacological treatment. Erratic L-dopa absorption due to the influence of food on gastric emptying[30] and the dissociation between L-dopa plasma concentration and clinical effect because of dietary neutral amino acids in the bloodstream[31] appear to be the chief factors generating the unpredictable element of motor fluctuations. However, the most effective dietary strategy involves redistribution of protein intake.[31] This requires protein to be virtually excluded in food taken during the day (protein content restricted to 7 g) with daily protein requirement being made up in a high-protein evening meal. Carter et al compared various diets in a group of fluctuating patients on standard oral L-dopa medication. While taking an average American amount of protein in their diet, these patients were "on" for 51% of the waking day. When protein intake was reduced to the RDA level, "on" time increased to 61% and when a protein redistribution diet was taken, patients remained "on" for 71% of the time.[35] The protein redistribution diet requires considerable reorganization of mealtimes, and patients have to accept a period of loss of response to medication following the higher-protein evening meal. Nevertheless, with appropriate dietary guidance and encouragement, the majority of patients are able to comply with the diet. About 60% of patients report improvement in control of motor symptoms and a more stable response to L-dopa, usually within a few days.[34] The diet offers no benefit to patients who do not fluctuate because of poor responsiveness to L-dopa.[34] Long-term experience with the protein redistribution diet suggests that 70% of patients who gain an initial advantage will use the diet for 12 months or more.[37] A study of the nutritional status in patients restricting daytime protein intake for 2 months showed that significant reduction in the intake of protein, calcium, phosphorus, iron, riboflavin, and niacin occurred.[38] However, only calcium intake fell to below the RDA level, probably because of a restriction on the intake of dairy products. Body weight and serum prealbumin concentration did not change significantly. Although dietary protein redistribution is an effective long-term treatment in some patients, careful monitoring of nutrition is required. This is of particular importance when the usual diet is marginally adequate and when patients are at risk for osteoporosis. Manipulation of dietary components other than protein has been studied less extensively. Carbohydrate loads, by stimulating insulin secretion, reduce circulating amino acid levels.[39] This may be the explanation for the observation that the effectiveness of oral L-dopa doses is enhanced by glucose loading.[40] Berry et al administered balanced carbohydrate:protein (ratio = 5) meals to Parkinsonian patients and found that plasma neutral amino acid levels did not change.[41] They suggested that the effect of carbohydrate in lowering amino acid concentration could cancel out the rise following a moderate protein load and that a balanced dietary intake may be as effective as protein restriction/redistribution. Limiting or redistributing protein intake may minimize competitive inhibition of transmembrane passage of L-dopa into the brain but may not be the best way to influence other forms of dietary interference with the action of L-dopa, particularly the effects of food on gastric emptying. Redistribution of the dietary energy content or adjustment of the fiber-type and viscosity of meals may allow more efficient access of L-dopa medication to absorption sites. These forms of dietary manipulation have not been systematically evaluated in Parkinson's disease. Meal size will also affect the time taken for gastric emptying. Small snacks taken with L-dopa medication do not significantly interfere with the clinical response to the drug.[42] However, dividing daily dietary intake into multiple small feedings rather than three standard meals does not improve the effectiveness of treatment.[33] selected refs: 6. Shoulson I, Glaubiger GA, Chase TN. On-off response: clinical and biochemical correlations during oral and intravenous levodopa administration In Parkinsonian patients. Neurology 1975;25:1144-8 15. Kempster PA, Frankel JP, Bovingdon M, Webster R, Lees AJ, Stern GM. Levodopa peripheral pharmacokinetics and duration of motor response in Parkinson's disease. J Neurol Neurosurg Psychiatry 1989; 52:718-23 17. Bianchine JR, Calimlim LR, Morgan JP, Dujovne CA, Lasagna L. Metabolism and absorption of L-3,4-dihydroxyphenylalanine in patients with Parkinson's disease. Ann NY Acad Sci 1971;179:126-40 18. Hunt JN, Stubbs DF. The volume and energy content of meals as determinants of gastric emptying. J Physiol 1975;245:209-25 19. Riviera-Calimlim L, Dujovne CA, Morgan JP, Lasagna L, Bianchine JR. Absorption and metabolism of L-dopa by the human stomach. Eur J Clin Invest 1971;1:313-20 20. Leon AS, Spiegel HE. The effect of antacid administration on the absorption and metabolism of levodopa. J Clin Pharmacol 1972;12:263-7 21. Schwartz SE, Levine RA, Singh A, Scheidecker JR, Track NS. Sustained pectin ingestion delays gastric emptying. Gastroenterology 1982;83:812-7 22. Rivera-Calimlim LR, Morgan JP,,Dujovne CA, Bianchine JR, Lasagne L. L-3,4-Dihydroxyphenylalanine metabolism by the gut in vitro. Biochem Pharmacol 1971;20:3051-7 24. Nutt JG, Woodward WR, Hammerstad JP, Carter JH, Anderson JL. "On-off" phenomenon in Parkinson's disease: relationship to levo-dopa absorption and transport. N EngI J Med 1984;310:483-8 25. Baruzzl A, Contin M, Riva R, et al. Influence of meal Ingestion time on pharmacokinetics of orally administered levo-dopa In Parkinsonian patients. Clin Neuropharmacol 1987;10:527-37 26. Wade DN, Mearick PT, Morris JL. Active transport of L-dopa in the intestine. Nature 1973;242:463-5 27. Wade LA, Katzman R. Synthetic amino acids and the nature of L-dopa transport at the blood-brain barrier. J Neurochem 1975;25:837-42 28. Frankel JP, Kempster PA, Bovingdon M, Webster R, Lees AJ, Stern GM. The effects of oral protein on the absorption of intraduodenal tevodopa and motor performance. J Neurol Neurosurg Psychiatry 1989;52:1063-7 29. Pardridge WN. Kinetics of competitive inhibition of neutral amino acid transport across the blood-brain batrier. J Neurochem 1977;28:103-8 30. Kurlan R, Rothfield KP, Woodward WR, et al. Erratic gastric emptying of levodopa may cause "random" fluctuations of Parkinsonian mobility. Neurology 1988;38:419-21 31. Pincus JH, Barry KM. Plasma levels of amino acids correlate with motor fluctuations In Parkinsonism. Arch Neurol 1987;44:10O-9 32. Mena I, Cotzias GC. Protein intake and treatment of Parkinson's disease. N EngI J Med 1975;292:181-4 33. Juncos JL, Fabbrini G, Mouradian MM, Serrati C, Chase TN. Dietary Influences on anti-Parkinsonian response to l-dopa. Arch Neurol 1987;44:1003-5 34. Riley D, Lang AE. Practical application of a low protein diet for Parkinson's disease. Neurology 1988;38:1026-3 43. Guggenheim M. Dioxphenylalanine, a new amino acid from Vicia faba. Z Physiol Chem 1913;88:276-84 44. Spengos M Vassilopoulos D. Improvement of Parkinson's disease after Vicia faba consumption. Book of abstracts, 9th International Symposium on Parkinson's disease 1988:46 45. Rabey JM, Vered Y, Shabtai H, Graff E, Korczyn AD. Improvement of Parkinsonian features correlate with high plasma levodopa values after broad bean (Vicia faba) consumption. J Neurol Neurosurg Psychiatry 1992;55:725-7 46. Kempster PA, Bogetic Z, Secombe JW, Martin HD, Balazs NDH, Wahlqvist ML. Motor effects of broad beans (Vicia faba) in Parkinson's disease: single dose studies. Asia Pac J Clin Nutr 1993;2:85-89 48. Andrews RS, Pridham JB. Structure of a dopa glucoside from Vicia faba. Nature 1965;205:1213-4 49. Miller ER. Dihydroxyphenylalanine, a constituent the velvet bean. J Biol Chem 1920;44:481-6 50. Damodaran M, Ramaswamy R. Isolation of L-3,4- dihydroxyphenylalanine from the seeds of Mucuna pruriens. Biochem J 1937;31:2149-52 If anyone can get me refs: 6, 15, 17,19,24,25,29,31, and/or 45, I would very much like to read them. If any are available on the net, I would appreciate a clue to locate. apology for being so long. -- ron 1936, dz PD 1984 Ridgecrest, California Ronald F. Vetter <[log in to unmask]> http://www.ridgecrest.ca.us/~rfvetter