Carbidopa
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Trade Name
Classification
Decarboxylase Inhibitor; antiparkinsonian adjunct
Dosage/Route
- * Dosage:
- – Carbidopa alone (Lodosyn): 25 mg tablets
- – Carbidopa/Levodopa (Sinemet): 10/100, 25/100, 25/250 mg (carbidopa/levodopa ratios)
- – Extended-release (Sinemet CR): 25/100, 50/200 mg
- * Route: Oral (PO)
Usual Dosage
- * Parkinson’s (with Levodopa):
- – IR: Start 25/100 mg PO TID; adjust to 70-100 mg/day carbidopa total (with levodopa titrated); max carbidopa 200 mg/day
- – CR: Start 50/200 mg PO BID; adjust every 3 days; usual 2-4 tablets/day
- * Carbidopa alone: 25 mg PO with each levodopa dose if additional inhibition needed
- * Titrate based on response; higher carbidopa reduces levodopa dose needed
Mechanism of Action
Inhibits peripheral aromatic L-amino acid decarboxylase (DOPA decarboxylase), preventing levodopa’s conversion to dopamine outside the brain. Increases levodopa availability to cross the blood-brain barrier, where it becomes dopamine to relieve Parkinson’s symptoms; reduces peripheral side effects
Side Effects & Adverse Effects
- * Side Effects (mostly from levodopa): Nausea, dizziness, dyskinesia (with levodopa)
- * Adverse Effects:
- – Orthostatic hypotension (levodopa-related)
- – Neuropsychiatric (hallucinations, confusion; levodopa effect)
- – GI upset (less with carbidopa vs. levodopa alone)
- – Rare (carbidopa-specific): Allergic reactions
Nursing Management (Implications & Teachings)
- * Implications:
- – Monitor BP (orthostasis), motor symptoms (on-off phenomenon), mental status
- – Assess levodopa efficacy (tremor, rigidity); carbidopa enhances it
- – Give on time (delays worsen symptoms); avoid high-protein meals (competes with levodopa absorption)
- – Don’t crush/chew CR tablets
- * Teachings:
- – Take same time daily; with food if nausea occurs (but low protein)
- – Rise slowly to avoid dizziness
- – Report uncontrolled movements, confusion, or fainting
- – Avoid vitamin B6 supplements (reverses carbidopa effect)
Indication for This Patient
Parkinson’s disease (adjunct to levodopa to enhance efficacy, reduce peripheral side effects like nausea)
Time
- * Timing: IR: TID-QID; CR: BID
- * Onset: Enhances levodopa effect within hours; full benefit weeks
- * Peak: IR: 1-3 hr (levodopa-driven); CR: 2-4 hr
- * Duration: Matches levodopa (4-6 hr IR; 6-8 hr CR)
