CARBIDOPA/LEVODOPA

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Safetychecker Summary for Carbidopa/Levodopa
(for details about the summarized interactions, read the full article)

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

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.

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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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over-the-counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2003.

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