What is levodopa/carbidopa? How does it interact with other drugs?

5-HTP (5-hydroxytryptophan)

Effect: Possible Harmful Interaction

The body uses the natural substance 5-HTP to manufacture serotonin, and
supplemental forms of 5-HTP have been used for treating
depression and migraine headaches. Since it is converted by the body to serotonin,
5-HTP might have antidepressant properties. For this reason, some people with
Parkinson’s-related depression have tried it.

However, the combination of 5-HTP and carbidopa might cause a scleroderma-like condition, in which the skin becomes hard and tight. Because of the risk of this side effect, persons taking levodopa/carbidopa for Parkinson’s disease should avoid supplemental 5-HTP.

Branched-Chain Amino Acids (BCAAs)

Effect: Possible Harmful Interaction

Branched-chain
amino acids (BCAAs) in supplement form have been used to
improve appetite in cancer patients and to slow the progression of
amyotrophic
lateral sclerosis (ALS, or Lou Gehrig’s disease). Dietary
protein can decrease the effectiveness of levodopa in Parkinson’s disease. Because
it is the amino acids in proteins that affect levodopa, BCAAs might cause the same
problem. Therefore, if one takes levodopa/carbidopa for Parkinson’s, it may be
advisable to avoid BCAAs and other amino acid supplements.

Iron

Effect: Take at a Different Time of Day

Iron appears to interfere with the absorption of both levodopa and carbidopa by
binding to them. Studies have found that blood levels of levodopa and carbidopa
are reduced 30 to 51 percent and 75 percent, respectively, by iron
supplementation, resulting in a worsening of symptoms of
Parkinson’s disease. Based on this finding, one should separate the times one
takes iron and these drugs by as long as possible.

Kava

Effect: Possible Harmful Interaction

The herb kava (Piper methysticum) has a sedative
effect and is used for anxiety and insomnia. A few case reports suggest that kava
might interfere with the action of dopamine in the body. This could at least
partially neutralize the therapeutic effects of levodopa. In one individual,
Parkinson’s disease symptoms got worse following supplementation with kava extract
of 150 milligrams (mg) twice daily for ten days. Based on these reports, it may be
advisable to avoid kava during levodopa/carbidopa therapy.

Traditional Chinese Herbal Medicine

Effect: Possible Reduced Action of Drug

Certain herbal formulas used in traditional Chinese herbal medicine to
treat upset stomach might reduce the effectiveness of levodopa.

Vitamin B6

Effect: Possible Reduced Action of Drug

If taking levodopa alone, one should not take more than 5 mg per day of
vitamin
B6
or it might impair the effectiveness of the
drug. However, if one uses levodopa/carbidopa combinations that provide a total
daily dose of at least 75 mg of carbidopa, this issue is not a concern.

Policosanol

Effect: Possible Benefits and Risks

Policosanol may increase both the effects and the side
effects of levodopa.

SAMe (S-adenosylmethionine)

Effect: Possible Benefits and Risks

SAMe is a naturally occurring compound derived from the amino acid methionine
and the energy molecule adenosine triphosphate (ATP). SAMe is
widely used as a supplement for treatment of osteoarthritis and depression.
Preliminary evidence suggests that levodopa might deplete levels of SAMe in the
body. This suggests (but definitely does not prove) that persons taking
levodopa/carbidopa might benefit from SAMe supplements.

One short-term (thirty-day) double-blind study suggests that such combination
treatment is safe and might help depression related to Parkinson’s
disease. However, there are also concerns that SAMe could
cause levodopa to be less effective over time. Persons taking levodopa/carbidopa
should consult their physician about taking SAMe.

Bibliography

Bottiglieri, T., K. Hyland, and E. H. Reynolds. “The Clinical Potential in Ademetionine (S-adenosylmethionine) in Neurological Disorders.” Drugs 48 (1994): 137-152.

Liu, X., N. Lamango, and C. Charlton. “L-dopa Depletes S-adenosylmethionine and Increases S-adenosyl Homocysteine: Relationship to the Wearing Off Effects.” Social Neuroscience 24 (1998): 1469.

Sunagane, N., et al. “Possibility of Interactions Between Prescription Drugs and OTC Drugs (2nd Report): Interaction Between Levodopa Preparation and OTC Kampo Medicines for Upset Stomach.” Yakugaku Zasshi 126 (2006): 1191-1196.