The oral therapy, produced by India-based Alembic Pharmaceuticals, will be available as extended-release tablets containing either 50 mg of carbidopa and 200 mg of levodopa, or 25 mg of carbidopa and 100 mg of levodopa.
Sinemet, marketed by Merck, was approved by the FDA in 2014 and is sold as controlled-release tablets in three different strengths: 25 mg of carbidopa and 100 mg of levodopa; 10 mg of carbidopa and 100 mg of levodopa; or 25 mg of carbidopa and 250 mg of levodopa.
People with Parkinson’s have low levels of the neurotransmitter dopamine in the brain. Neurotransmitters are substances produced in response to nerve signals that act as chemical messengers. Direct administration of dopamine cannot be used to increase its levels because it is unable to reach the brain due to the blood-brain barrier, a thin membrane that protects the central nervous system (brain and spinal cord) from the circulatory blood system.
Levodopa and carbidopa act to increase dopamine levels in the brain. Levodopa, a molecule involved in the chemical reaction that produces dopamine, has the ability to cross the blood-brain barrier.
Meanwhile, Carbidopa inhibits enzymes known as decarboxylases that would degrade levodopa, ensuring it reaches the brain. However, carbidopa cannot cross the blood-brain barrier, which allows decarboxylases in the brain to then convert the levodopa to dopamine. Using carbidopa together with levodopa enables the use of lower doses of levodopa, which decreases its side effects, including nausea and vomiting.
The carbidopa and levodopa extended-release tablets also are approved for treatment of postencephalitic parkinsonism, a progressive neurodegenerative disease with clinical features of Parkinson’s, likely caused by an infection, and for people with Parkinson’s symptoms following intoxication by carbon monoxide or manganese.
Brief exposure to air pollution, including to carbon monoxide, has been suggested to increase the risk of Parkinson’s disease and other neurological diseases.
Exposure to the metal manganese may trigger the development of Parkinson’s by promoting the release from nerve cells of the alpha-synuclein protein. The clustering of this protein causes inflammation and neurodegeneration.