Antiparkinsonian Drugs
Antiparkinsonian drugs are medications used to treat the symptoms of Parkinson's disease—a progressive neurological disorder characterized by motor symptoms such as tremors, rigidity, bradykinesia, and postural instability. These drugs work by addressing the imbalance of neurotransmitters in the brain, particularly the reduction in dopamine levels.
Classification
- Dopamine Precursors:
- Levodopa (often combined with Carbidopa to prevent peripheral metabolism)
- Dopamine Agonists:
- Pramipexole, Ropinirole, Bromocriptine
- MAO-B Inhibitors:
- Selegiline, Rasagiline
- COMT Inhibitors:
- Entacapone, Tolcapone
- Anticholinergics:
- Benztropine (also trihexyphenidyl is used in some settings)
- Amantadine:
- Amantadine (has both dopaminergic and anticholinergic effects)
Pharmacodynamics
- Dopamine Precursors:
- Levodopa is converted to dopamine in the brain, which helps replenish depleted dopamine levels and improves motor control.
- Dopamine Agonists:
- These drugs directly stimulate dopamine receptors, mimicking the action of dopamine to reduce motor symptoms.
- MAO-B Inhibitors:
- Selegiline and rasagiline inhibit monoamine oxidase-B, an enzyme that breaks down dopamine, thereby increasing its availability and prolonging its effects.
- COMT Inhibitors:
- Entacapone and tolcapone inhibit catechol-O-methyltransferase, an enzyme that metabolizes levodopa, resulting in increased and prolonged dopamine levels in the brain.
- Anticholinergics:
- Drugs such as benztropine reduce the activity of acetylcholine, helping to restore the balance between dopamine and acetylcholine and alleviating symptoms like tremors.
- Amantadine:
- Exerts both dopaminergic effects (enhancing dopamine release) and anticholinergic effects (blocking glutamate receptors), which helps reduce dyskinesia and other Parkinsonian symptoms.