Antiparkinsonian

Antiparkinsonian

Antiparkinsonian drugs are medications used to treat the symptoms of Parkinson's disease and other forms of parkinsonism. These drugs aim to manage the motor symptoms such as tremor, rigidity, bradykinesia, and postural instability, which are characteristic of these conditions.

Mechanism of Action

Parkinson's disease is primarily caused by the degeneration of dopaminergic neurons in the substantia nigra of the brain, leading to a deficiency of dopamine in the striatum. Antiparkinsonian drugs work by either replenishing dopamine levels, mimicking dopamine action, or modulating other neurotransmitter systems to restore balance.

Dopaminergic Agents

1. Levodopa: The most effective treatment for Parkinson's disease. It is a precursor to dopamine that can cross the blood-brain barrier and is converted to dopamine in the brain.

  - Often combined with carbidopa or benserazide to prevent peripheral conversion of levodopa to dopamine, which reduces side effects and increases availability in the brain.

2. Dopamine Agonists: These drugs directly stimulate dopamine receptors.

  - Examples include pramipexole, ropinirole, and rotigotine.

3. MAO-B Inhibitors: These inhibit the enzyme monoamine oxidase B, which breaks down dopamine in the brain.

  - Examples include selegiline and rasagiline.

4. COMT Inhibitors: These inhibit the enzyme catechol-O-methyltransferase, which breaks down dopamine.

  - Examples include entacapone and tolcapone.

Anticholinergic Agents

These drugs help reduce tremor and muscle rigidity by blocking the action of acetylcholine, a neurotransmitter that is in relative excess in Parkinson's disease due to dopamine deficiency.

  - Examples include trihexyphenidyl and benztropine.

NMDA Receptor Antagonists

1. Amantadine: Originally an antiviral drug, it has antiparkinsonian effects by modulating glutamatergic transmission and increasing dopamine release.

Side Effects

Antiparkinsonian drugs can have a range of side effects, which vary depending on the class of drug:

- Levodopa: Long-term use can lead to motor complications such as dyskinesias and "on-off" phenomena. - Dopamine Agonists: May cause nausea, hallucinations, sleep disturbances, and impulse control disorders. - MAO-B Inhibitors: Generally well-tolerated but can cause insomnia and headache. - Anticholinergics: Can cause dry mouth, blurred vision, constipation, and cognitive impairment, especially in older adults.

Clinical Use

The choice of antiparkinsonian medication depends on the stage of the disease, the specific symptoms, and the patient's overall health. Levodopa remains the most effective treatment for motor symptoms, but other drugs are often used in combination to manage symptoms and reduce side effects.

Also see

- Parkinson's disease - Dopamine - Substantia nigra - Neurotransmitter - Blood-brain barrier

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