Generic Name

Duopa

Mechanism

• Levodopa (L‑dopa) is a bio‑available precursor to dopamine, diffusing across the blood‑brain barrier and converting to dopamine via aromatic L‑amino acid decarboxylase.
• Carbidopa inhibits peripheral decarboxylase, reducing peripheral levodopa metabolism, thereby:
• Increasing central levodopa delivery.
• Diminishing peripheral side effects (nausea, orthostatic hypotension).
• Continuous infusion mitigates motor fluctuations (“on‑off” phenomena) seen with oral dosing, maintaining steadier dopamine levels.

Pharmacokinetics

Indications

• Advanced Parkinson’s disease requiring deep brain stimulation surgery postponement or unsatisfactory oral therapy.
• Motor fluctuations with disabling “off” periods (>2 h) affecting quality of life.
• Patients capable of undergoing jejunostomy and enteral catheter placement.

Contraindications

• Contraindications:
• Known hypersensitivity to levodopa, carbidopa, or gel components.
• Severe GI dysfunction (e.g., obstruction, severe motility disorders) preventing jejunal infusion.
• Warnings:
• Cardiovascular: risk of arrhythmias, especially in uncontrolled hypertension or heart disease.
• Psychiatric: potential for hallucinations, addiction, or worsening compulsive behaviors.
• Renal: dose adjustment for GFR <30 mL/min/1.73 m².
• Precautions:
• Monitor for orthostatic hypotension; caution in elderly, bedridden patients.
• Should be used when oral levodopa/carbidopa tolerance is insufficient or causes dyskinesia.

Dosing

• Preparation: Dilute 100 mg levodopa/10 mg carbidopa reconstituted with sterile water (e.g., 3 mL).
• Infusion: Continuous IV infusion via jejunostomy tube using a dedicated pump.
• Maintenance dose: 200–300 mg levodopa/20–30 mg carbidopa per 24 h (adjust 0.8 × dose for renal impairment).
• Loading dose: 200‐300 mg levodopa/20‑30 mg carbidopa over 1–2 hr for rapid onset.
• Failure of therapy: If inadequate response, consider adding MAO‑B inhibitors (selegiline) or COMT inhibitors (entacapone) to the pump mixture.

Adverse Effects

• Common:
• Nausea, vomiting (less frequent due to carbidopa).
• Diarrhea, abdominal discomfort from infusion.
• Sleepiness, vivid dreams.
• Oral mucosal dryness.
• Serious:
• Orthostatic hypotension leading to falls.
• Nervous system: dyskinesia, hallucinations, impulse control disorders.
• Cardiac: arrhythmias, QT prolongation.
• Infection: percutaneous tunnel infection, T‑insertion site.
• Respiratory: aspiration risk if nasogastric tube placed.

Monitoring

• Clinical:
• Unified Parkinson’s Disease Rating Scale (UPDRS) motor and OFF/ON times.
• Quality of life assessments.
• Dyskinesia severity (Abnormal Involuntary Movement Scale).
• Laboratory:
• CBC, electrolytes, renal panel (baseline & quarterly).
• Liver function tests when adding MAO‑B inhibitors.
• Device‑related:
• Catheter site inspection every 48–72 hrs.
• Pump function verification weekly.

Clinical Pearls

• Continuous infusion, not cyclic dosing: Duopa provides a steadier dopamine level that better controls motor fluctuations than traditional oral “load‑high” regimens.
• Peri‑operative management: If patient requires a surgical procedure, stop Duopa infusion 24 h pre‑op; resume 12 h post‑op when fully hemodynamically stable.
• Renal adjustment: For patients with CKD stage 3–4, reduce maintenance dose to 50 % of the standard and check serum creatinine before each refill.
• Psychiatric caution: Screen for impulse‑control disorders before initiating Duopa; consider concurrent use of PRN pramipexole or dopamine agonists only if benefits outweigh risks.
• Drug interactions: Concomitant MAO‑A inhibitors (phenelzine) are contraindicated; avoid strong CYP2D6 inhibitors that block peripheral decarboxylase.
• Home nursing visits: Schedule one‑hour pump management training for the patient or caregiver; provide a backup infusion bag for emergencies.

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