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Carbidopa/Levodopa

Also indexed as: Atamet®, Sinemet®

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.

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.

Summary of Interactions for Carbidopa/Levodopa

Depletion or interference Niacin*
Adverse interaction None known
Side effect reduction/prevention None known
Supportive interaction Vitamin C*
Reduced drug absorption/bioavailability Iron
Other (see text) 5-HTP
Vitamin B6

For the convenience of the reader, the information in the summary is categorized as follows: “Depletion or interference” indicates the drug may deplete or interfere with the absorption or function of the supplement or herb. “Adverse interaction” indicates that the supplement or herb used together with the drug may result in undesirable effects. “Side effect reduction/prevention” indicates the supplement or herb may reduce the likelihood and/or severity of a potential side effect caused by the drug. “Supportive interaction” indicates the supplement or herb may support or aid the function of the drug. “Reduced drug absorption/bioavailability” indicates that the supplement or herb may decrease the absorption and/or activity of the drug in the body. An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

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.