Levodopa is required by the brain to produce dopamine, an important neurotransmitter. People with Parkinson’s disease have depleted levels of dopamine, leading to debilitating symptoms. Levodopa is given to increase production of dopamine, which in turn reduces the symptoms of Parkinson’s disease. When taken by mouth, most levodopa is broken down by the body before it reaches the brain. Sinemet® combines levodopa with carbidopa, a drug that prevents the breakdown, allowing levodopa to reach the brain to increase dopamine levels.
Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.
 May be Beneficial: Depletion or interference—The medication may deplete or interfere with the absorption or function of the nutrient. Taking these nutrients may help replenish them. | Niacin* |
| May be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better. | Vitamin C* |
 Avoid: Reduced drug absorption/bioavailability—Avoid these supplements when taking this medication since the supplement may decrease the absorption and/or activity of the medication in the body. | Iron |
 Check: Other—Before taking any of these supplements or eating any of these foods with your medication, read this article in full for details. | 5-HTP Vitamin B6 |
| Side effect reduction/prevention | None known |
| Adverse interaction | None known |
An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.
Interactions with Dietary Supplements
Vitamin B6
Vitamin B6 supplementation above 5–10 mg per day reduces the effectiveness of levodopa.1 However, combining levodopa with carbidopa prevents this adverse effect, so vitamin B6 supplements may safely be taken with Sinemet® (carbidopa/levodopa).
Iron
Iron supplements taken with carbidopa interfere with the action of the drug.2 People taking carbidopa should not supplement iron without consulting the prescribing physician.
5-Hydroxytryptophan (5-HTP)
Several cases of scleroderma-like illness have been reported in patients using carbidopa and 5-HTP.3 4 5 People taking carbidopa should not supplement 5-HTP without consulting the prescribing physician.
Niacin
A study in animals has found that carbidopa inhibits an enzyme involved in the synthesis of niacin in the body.6 In addition, there is evidence that niacin synthesis is decreased in people taking carbidopa and other drugs in its class.7 Further studies are needed to determine whether niacin supplementation is appropriate in people taking carbidopa.
Vitamin C
Combining levodopa-carbidopa and vitamin C may be useful for people with Parkinson’s disease whose motor complications are not effectively managed with conventional drug treatment. This combination was administered to people with Parkinson’s disease in a preliminary study.8 The researchers reported several improvements in participants who completed the study; however, 62% of the participants withdrew from the study, most citing difficulty in performing normal movements. Until more research is performed, this drug-nutrient combination must be viewed as experimental.
Interactions with Foods and Other Compounds
Food
Food, especially foods high in protein, can alter levodopa absorption.9 10 However, Sinemet® is often taken with food to avoid stomach upset. Sinemet® and Sinemet® CR should be taken at the same time, always with or always without food, every day.
References
1. Trovato A, Nuhlicek DN, Midtling JE. Drug-nutrient interactions. Am Family Phys 1991;44:1651–8.
2. Campbell NR, Hasinoff BB. Iron supplements: a common cause of drug interactions. Brit J Clin Pharmacol 1991;31:251–5 [review].
3. Sternberg EM, Van Woert MH, Young SN, et al. Development of a scleroderma-like illness during therapy with L-5-hydroxytryptophan and carbidopa. New Engl J Med 1980;303:782–7.
4. Joly P, Lampert A, Thromine E, Lauret P. Development of pseudobullous morphea and scleroderma-like illness during therapy with L-5-hydroxytryptophan and carbidopa. J Am Acad Dermatol 1991;25:332–3.
5. Auffranc JC, Berbis P, Fabre JF, et al. Sclerodermiform and poikilodermal syndrome observed during treatment with carbidopa and 5-hydroxytryptophan. Ann Dermatol Verereol 1985;112:691–2.
6. Bender DA, Smith WR. Inhibition of kynurenine hydrolase by benserazide, carbidopa and other aromatic hydrazine derivatives: evidence for sub-clinical iatrogenic niacin deficiency. Biochem Soc Trans 1978;6:120–2.
7. Bender DA, Earl CJ, Lees AJ. Niacin depletion in Parkinsonian patients treated with L-dopa, benserazide and carbidopa. Clin Sci 1979;56:89–93.
8. Linazasoro G, Gorospe A. Treatment of complicated Parkinson disease with a solution of levodopa- carbidopa and ascorbic acid. Neurologia 1995;10:220–3 [in Spanish].
9. Threlkeld DS, ed. Central Nervous System Drugs, Antiparkinson Agents, Levodopa. In Facts and Comparison Drug Information. St. Louis, MO: Facts and Comparisons Drug Information, Apr 1998, 289p–90a.
10. Threlkeld DS, ed. Central Nervous System Drugs, Antiparkinson Agents, Levodopa. In Facts and Comparison Drug Information. St. Louis, MO: Facts and Comparisons Drug Information, Apr 1998, 289p–90a.
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2006-09-07
