Carbidopa-Levodopa, Levodopa, Carbidopa/Levodopa, Levodopa-Carbidopa, Levodopa/Carbidopa, Sinemet, Stalevo, Dopa decarboxylase inhibitor, Dopamine Precursor, Rytary, Duopa, Inbrija

  • Indications
  1. Parkinsonism
  2. Restless Leg Syndrome (off-label)
  3. Dopa Responsive Dystonia (off-label)
  • Mechanism
  1. Levodopa is decarboxylated to Dopamine in the Central Nervous System (CNS)
    1. Dopamine is unable to cross the blood brain barrier
  2. Levodopa is combined with carbidopa, a peripheral decarboxylase inhibitor
    1. Carbidopa blocks the peripheral decarboxylation of Levodopa
    2. Without carbidopa, 99% of Levodopa would undergo peripheral decarboxylation and fail to reach the CNS
    3. Carbidopa also reduces peripheral Dopamine adverse effects (e.g. Orthostatic Hypotension, Nausea, Vomiting)
  • Pharmacokinetics
  1. Rapidly absorbed orally
  2. Half-Life (non-sustained release): 1 to 3 hours
  • Precautions
  • General pointers
  1. Levodopa/Carbidopa (Sinemet, regular release) is by far the single most effective agent in Parkinsonism
    1. This agent should be the first line and main agent used for Parkinsonism
    2. All other agents are adjuncts only
  2. Dosing Threshold
    1. Identify the individual patient's optimal dose and use this dose at each dosing interval
    2. Using a lower dose below threshold will be inadequate
  3. Food Interactions
    1. Take at least one hour before a meal or 2 hours after a meal
    2. Levodopa is absorbed in the Small Intestine and impacted by gastric emptying
  4. Wearing off of effect
    1. See frequency of dosing of Sinemet below
    2. Most common cause of Insomnia
    3. May cause anxiety, nocturnal cramps
    4. Duration of activity decreases with longterm use
      1. First 2 to 5 years of use: Consistent 5-6 hours of effect
      2. After 5-8 years: Motor fluctuations, Dyskinesia (on-off effect impacting mobility)
      3. Longterm: Progressive disorders of balance, gait, speech, Swallowing
  5. Dyskinesia (e.g. Choreiform movements)
    1. Dyskinesia is more age related than that of duration of Levodopa use
    2. Reducing each Levodopa dose decreases this adverse effect
    3. Amantadine decreases Dyskinesia
  6. Adverse Effects: Educate patients about serious effects (most are reduced by tapering dose)
    1. Drowsiness
    2. Pathologic Gambling, Hypersexuality, Excessive shopping/spending
    3. Hallucinations or Delusions
    4. Swelling
  1. Carbidopa/Levodopa (Sinemet, Immediate Release)
    1. Preferred option over sustained release
      1. Lower cost
      2. Better Pharmacokinetics
      3. Less Drug Interactions
    2. Dosing
      1. Start at 25 mg/100 mg (or 10 mg/100 mg) orally three times daily
      2. Increase by on half to one tablet every 1-2 days as needed
      3. Maximum : 3 tablets per dose, three times daily (no benefit to higher doses, but frequency may be increased)
    3. Frequency of dose
      1. Initially give dose three times daily
      2. Long term, dose may wear off early
        1. Frequency may need to be increased to every 6 hours (at same number of tablets at each dose)
    4. Emergency Dosing (rescue dose for hypomobility, "off" episode)
      1. Crushed Carbidopa/Levodopa tablets may be dissolved in carbonated beverage
  2. Carbidopa/Levodopa Controlled Release (Sinemet CR)
    1. Start at 50/200 orally twice daily
      1. Convert 300-400 mg Levodopa immediate release/day to start CR 200 mg Levodopa twice daily
      2. Convert 500-600 mg Levodopa immediate release/day to start CR 300 mg Levodopa twice daily
      3. Convert 700-800 mg Levodopa immediate release/day to start CR 800 mg/day Levodopa divided three times daily
      4. Convert 900-1000 mg Levodopa immediate release/day to start CR 1000 mg/day Levodopa divided three times daily
    2. Increase by one tablet every 3 days as needed
    3. Maximum : 8 tablets daily
    4. No benefit over immediate release in motor function, and absorption may be sporadic in some patients
  3. Carbidopa/Levodopa fast onset, sustained release (Rytary)
    1. Start with lowest dose 23.75/95 mg orally three times daily
      1. May increase to 36.25/145 mg orally three times daily after 3 or more days
    2. Typical Dose: 3-4 caps three times daily
    3. Maximum: 97.5 mg/390 mg three times daily
    4. Onset within 1 hour, duration of 6 hours
    5. Costs 3-4 times more than generic Carbidopa/Levodopa
    6. May decrease "off time", the wearing off of activity between doses
    7. Consider in advanced Parkinsonism for "off time" problems despite four time daily dosing
    8. Requires higher dosing than other preparations due to lower Bioavailability
    9. (2015) Presc Lett 22(7): 41
  4. Carbidopa/Levodopa/Entacapone (Stalevo)
    1. Start at 12.5/50/200 orally twice daily
    2. Increase slowly
    3. Maximum : 8 tablets daily
  5. Carbidopa/Levodopa Enteral Suspension (Duopa)
    1. Consider for refractory on-off effects with oral dosing (suspension may have more consistent absorption and sustained effects)
    2. Convert from immediate release dosing to administer over 16 hours (max daily dose 2000 mg)
    3. Enteral suspension delivered via GJ-Tube with portable infusion pump over 16 hours
    4. Consider following infusion with a nighttime oral immediate release dose
  6. Inbrija (inhaled Levodopa)
    1. Indicated in off-time motor rigidity or Tremor
    2. Rapid onset (10 min after inhalation) and duration of 1 hour used for prn "off time" rigidity or Tremor
    3. Less expensive ($30/dose) than Apokyn ($200/dose), an injectable option for off-time
    4. Requires dexterity to replace capsule in Inhaler
    5. Avoid in underlying lung disease (e.g. Asthma, COPD) due to bronchospasm risk
    6. (2019) Presc Lett 26(5)
  1. Restless Leg Syndrome
    1. Start Carbidopa/Levodopa (Immediate Release) 1/2 of a 25 mg/100 mg orally at bedtime
    2. Titrate to effect increasing by 1/2 tablet every 3-4 days to a maximum of 2 tablets (50 mg/200 mg) at bedtime
    3. May use a combination of immediate release and controlled release Carbidopa/Levodopa if symptomatic night awakenings
  2. Dopa Responsive Dystonia
    1. Start Carbidopa/Levodopa (Immediate Release) 25 mg/100 mg tablet orally daily
    2. Titrate to effect (maximum Levodopa 1000 mg/day)
  • Drug Interactions
  1. Pyridoxine
    1. Stimulates decarboxylation (may prevent Levodopa from reaching CNS)
  2. Antipsychotic agents
    1. Block Dopamine receptors
  3. MAO Inhibitors
    1. MAO Inhibitors increase Sympathomimetic amine accumulation
    2. Stop non-selective MAO Inhibitors at least 2 weeks prior to Levodopa start
  4. Anticholinergic Agents
    1. Anticholinergic Agents slow gastric emptying, delay absorption, but may increase overall Levodopa levels
  • Safety
  1. Pregnancy Category C
  2. Avoid in Lactation