Norepinephrine NE neurotransmitters formation start with the uptake of tyrosine into the cytoplasm. Dopamine is transformed into dopa then to dopamine which converted in the storage vesicles into norepinephrine. NE is metabolized in synaptic cleft by COMT

Different drugs pass through four major pharmacokinetic processes in the body; absorption, metabolism, distribution and finally elimination.

The main target of antiparkinsonian drugs is to increase the dopamine concentration and activity in the brain. Levodopa is transformed into dopamine in the brain, DDC and COMT inhibitors decrease the peripheral metabolism of levodopa. Dopamine agonists a

There are two major phases of drug metabolism; phase I and phase II. In phase I; a hydrophilic group is added or unmasked in the drug. Cytochrome P450 isozyme system play important role in phase I. In phase II more lipophilic groups are conjugated to the