Everything you need to know about Levodopa, and some Little-known facts

Levodopa

Uses of Levodopa

  • First-line treatment for Parkinson’s disease
  • Alleviates rigidity in Parkinson’s patients
  • Reverses hypokinesia
  • Helps reduce tremors

Class of Drug

  • Anti-Parkinsonian drug
  • Prodrug of dopamine

Mode of Administration and Dosage of Levodopa

  • Oral administration in tablet form (0.5 g)
  • Usual dosage: 2-3 g per day

Mechanism of Action of Levodopa

  • Parkinson’s disease patients require dopamine, which cannot cross the blood-brain barrier when administered directly.
  • Levodopa, as a prodrug, crosses the blood-brain barrier and is converted into dopamine by the enzyme dopamine carboxylase.
  • Once converted, dopamine becomes available for utilization by the brain.

Metabolism of Levodopa

  • The small intestine rapidly absorbs Levodopa.
  • Slower gastric emptying can impair the absorption of levodopa, as the gut wall may degrade the drug.
  • It undergoes first-pass metabolism.
  • The half-life of levodopa in plasma is approximately 1-2 hours.
  • Metabolites of the drug are excreted in urine following conjugation.

Levodopa Toxicity

  • Excessive amounts of levodopa in the blood can damage neuronal cells.
  • High levels of levodopa in peripheral nerves may cause an increase in epinephrine and norepinephrine concentrations in the blood.

Adverse Effects of Levodopa

  • Peripherally Acting Adverse Effects:
    • Nausea and vomiting (treated with Domperidone)
    • Postural hypotension
    • Mydriasis (dilation of pupils)
    • Arrhythmia
  • Centrally Acting Adverse Effects:
    • Dyskinesia (treated with Levetiracetam)
    • Psychosis (treated with Clozapine)
    • Hypersexuality
    • Impulsive gambling

Contraindications of Levodopa

  • Angle-closure glaucoma
  • Melanoma
  • Concomitant use with pyridoxine (vitamin B6) is contraindicated

Additional Information

  • Levodopa is commonly combined with carbidopa.
  • Carbidopa inhibits the peripheral activity of the enzyme dopa decarboxylase, allowing Levodopa to act exclusively in the brain.
  • The combination of Levodopa and Carbidopa enhances the drug’s effectiveness.
  • Drugs such as Entacapone and Selegiline are used to prolong the action of Levodopa.