Pramipexole

Action:
It is a dopamine agonist.

Uses:It is used in early stages in the treatment of Parkinson's disease.

Levodopa

It is a levorotatory form of dopa i.e. L-dopa. It is a naturally occuring amino acid in certain foods and herbs.

Action:
It is converted into dopamine in the brain and body with the help of the enzyme dopa decarboxylase .

Uses:
It is used in the treatment of Parkinson's disease.

Entacapone

It is an anti-Parkinsonian drug.

Action:
It acts as Catechol-O-Methyl Transferase (COMT) inhibitor and helping levodopa to reach the brain easily by reducing its biotransformation.
It works effectively if taken alongwith levodopa and carbidopa i.e. combination of levodopa, carbidopa and entacapone (LCE). It has also been found that this combination did not increase motor complications.

Uses:
It is used in the treatment of Parkinson's disease. It has been found that prolonged treatment with entacapone results in enhanced response to levodopa in Patients of Parkinson's disease.

References:
Hauser, R. A.; Panniset, M.; 2008. Double-blind trial of levodopa/carbidopa/entacapone versus levodopa/carbidopa in early Parkinson's disease. Movement disorders, Vol. 24, No. 4, Pages 541-550.

Rinne, U. K., Larson, J. P. et al. 1998. Entacapone enhances the response to levodopa in parkinsonian patients with motor fluctuations. Neurology, Vol. 51, No. 5. Pages. 1309-1314.

Carbidopa

Action:
It causes inhibition of the peripheral metabolism of levodpa results in helping levodopa to reach the brain easily.

Uses:
It is used in combination with levodopa for the patients of Parkinson's disease.