Drugs Used in Parkinson’s Disease

This article explains about the Drugs for Parkinson’s disease improve dopamine levels or reduce symptoms like tremors and stiffness.

1. Dopaminergic Agents

   • Levodopa + Carbidopa
     • Levodopa is a precursor to dopamine that crosses the blood-brain barrier.
     • Carbidopa inhibits peripheral DOPA decarboxylase, preventing conversion of levodopa to dopamine outside the CNS, thus increasing its bioavailability in the brain and reducing peripheral side effects.

   • Adverse Effects:

     • Nausea, vomiting
     • Orthostatic hypotension
     • Dyskinesias
     • “On-off” and “wearing-off” phenomena with long-term use

2. Dopamine Agonists

   • Act directly on dopamine receptors (mostly D2).

   • Examples:

     • Bromocriptine (ergot derivative)
     • Pramipexole, Ropinirole (non-ergot derivatives)

   • Adverse Effects:

     • Sedation, hallucinations
     • Impulse control disorders (e.g., gambling, hypersexuality)
     • Nausea, peripheral edema

3. MAO-B Inhibitors

   • Inhibit monoamine oxidase-B, which metabolizes dopamine in the CNS.

   • Examples:

     • Selegiline
     • Rasagiline

   • Uses:

     • Early disease or as adjunct to Levodopa
     • Can delay need for Levodopa

   • Adverse Effects:

     • Insomnia
     • Serotonin syndrome if combined with SSRIs

4. COMT Inhibitors

   • Inhibit catechol-O-methyltransferase, an enzyme that degrades levodopa and dopamine.

   • Examples:

     • Entacapone (peripheral)
     • Tolcapone (peripheral and central)

   • Uses:

     • Extend Levodopa duration
     • Used for motor fluctuations

   • Adverse Effects:

     • Diarrhea
     • Liver toxicity (Tolcapone)
     • Orange discoloration of urine

5. Anticholinergics

   • Block muscarinic receptors to reduce cholinergic activity, restoring balance between dopamine and acetylcholine.

   • Examples:

     • Benztropine
     • Trihexyphenidyl

   • Uses:

     • Best for tremor and rigidity

   • Adverse Effects:

     • Dry mouth, blurred vision, constipation, urinary retention
     • Cognitive impairment (especially in elderly)

6. Amantadine

   • Originally an antiviral agent; increases dopamine release and inhibits dopamine reuptake. Also has NMDA receptor antagonistic activity.

   • Uses:

     • Mild Parkinsonism
     • Useful in reducing levodopa-induced dyskinesia

   • Adverse Effects:

     • Confusion, hallucinations
     • Livedo reticularis
     • Peripheral edema

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