Uses of this Supplement
Multiple Sclerosis
Parkinson's Disease
Rheumatoid Arthritis
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Levodopa-containing Medications
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Look Up > Supplements > Phenylalanine > Interactions
Interactions with Phenylalanine

In situ, phenylalanine (up to 100 mM) decreased the absorption of isotonic perfusion solutions of baclofen (0.5 mM) in the rat small intestine by 67% (Cejudo-Ferragud et al. 1996). To maximize absorption of the drug, baclofen should not be administered with meals, especially meals high in protein content.


Infusion of L-phenylalanine prior to administration of 3-O-methyl-6-[18F]fluoro-L-DOPA (18F-DOPA) prevented 18F-DOPA uptake in the brain (Doudet et al. 1992). L-phenylalanine improved specific-to-non-specific contrast images of 18F-DOPA during positron emission tomography (PET) scanning.


Administration of levodopa (1 mg/kg/hour IV) following administration of phenylalanine (100 or 200 mg/kg po) in two patients with advanced Parkinson's disease altered the clinical effects of the drug (Woodward, et al. 1998). The therapeutic response to levodopa could be diminished when administered at the same time as phenylalanine.


Cejudo-Ferragud E, Nacher A, Polache A, Cercos-Fortea T, Merino M, Casabo VG. Evidence of competitive inhibition for the intestinal absorption of baclofen by phenylalanine, Int J of Pharm (Amsterdam). 1996;132:63-69.

Doudet D, McLellan CA, Aigner TG, Wyatt RJ, Cohen RM. Delayed L-phenylalanine infusion allows for simultaneous kinetic analysis and improved evaluation of specific-to-non-specific fluorine-18-DOPA uptake in brain. J of Nucl Med. 1992;33(7):1383-1389.

Woodward, WR, Olanow CW, Beckner Rm et al. The effect of L-dopa infusions with and without phenylalanine challenges in parkinsonian patients. Neurol. 1998;48:1704-1708.

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