Psychiatric Drugs and Medications Q 35

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The nurse evaluates that carbidopa and levodopa (Sinemet) is therapeutically effective if the client has:

  

     A. Decreased GI responses

     B. Increased tolerance to pyridoxine

     C. Decreased tremors at rest

     D. Increased urinary output

    

    

Correct Answer: C. Decreased tremors at rest

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Carbidopa and levodopa help restore the balance between dopamine and acetylcholine, thereby controlling the responses of Parkinson’s disease. Carbidopa is indicated for combination use with levodopa (L-dopa) for the treatment of motor symptoms encountered in Parkinson disease (PD), post-encephalitic parkinsonism, and parkinsonism symptoms resulting from intoxication by carbon monoxide or manganese.

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Option A: Carbidopa, 1-?-methyldopa hydralazine, acts by irreversibly binding pyridoxal 5?-phosphate (PLP), therefore inhibiting l-aromatic amino acid decarboxylase (AADC), a PLP-dependent enzyme. AACD acts to metabolize 5-HTP to serotonin and L-dopa to dopamine. Whereas levodopa is taken up by the central nervous system, carbidopa cannot cross the blood-brain barrier, and therefore its effects on enzymatic activity act only peripherally.

Option B: Decreasing levodopa metabolism peripherally allows for more L-dopa to be taken up by the CNS. This increased potency reduces the dose of levodopa necessary for effective treatment of parkinsonian motor symptoms by up to 75%.

Option D: Additionally, the lack of peripheral conversion of levodopa to dopamine decreases gastrointestinal (GI) absorption, preventing excess dopamine in the GI tract, which decreases levodopa side effects, including diarrhea, nausea, and/or vomiting.

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