It should be on the market in two to three years. There are two primary classifications of drugs used to treat Parkinson's disease. One classification would include levodopa and the enzyme inhibitors that assist the brain absorption and enhance the duration of action of the dopamine that is made from levodopa, and the other classification of drugs includes the dopamine agonists. Sinemet is a combination of levodopa and a decarboxylase-inhibitor called carbidopa. These medications directly stimulate the dopamine receptors which are many times unable to be stimulated by Sinemet because of the death of cells in the substantia nigra and its connections to the dopamine receiving centers in the caudate nucleus and putamen.
Dopamine is a neurotransmitter in the brain.
There are two clinically significant dopamine pathways in the brain. One dopamine pathway emanates from the substantia nigra and enervates the caudate nucleus and putamen. This is the motor pathway of dopamine and is affected in Parkinson's disease with progressive death of the neurons in the substantia nigra. The second dopamine pathway emanates from the midbrain tegmentum and enervates the limbic system and orbital-frontal cerebral cortex. This second system is overactive in patients with schizophrenia.