Levodopa Leucine

H Lennernas, D Nilsson, S-M Aquilonius, D Ahren-stedt, L Knutson, LK Paalzow. The effect of L-leucine on the absorption of levodopa, studied by regional jejunal perfusion in man. Br J Clin Pharmacol 35 343— 250, 1993. 

Absorption and metabolism The drug is absorbed rapidly from the small intestine (when empty of food). Levodopa has an extremely short half-life (1 to 2 hours), which causes fluctuations in plasma concentration. This may produce fluctuations in motor response ( on-off phenomenon), which may cause the patient to suddenly lose normal mobility and experience tremors, cramps, and immobility. Ingestion of meals, particularly if high in protein content, interferes with the transport of levodopa into the CNS. Large, neutral amino acids (for example, leucine and isoleucine) compete with levodopa for absorption from the gut and for transport across the blood-brain barrier. Thus levodopa should be taken on an empty stomach, typically 45 minutes before a meal. Withdrawal from the drug must be gradual. 

A study found that the clinical response to a constant intravenous infusion of levodopa in 4 patients was unchanged by glycine and tysine but was reduced by phenylalanine, leucine and isoleucine, although the plasma levodopa levels remained unchanged. ... 

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