The FDA has required that the labels of all carbidopa/levodopa-containing products (Crexont, Dhivy, Duopa, Rytary, Sinemet, Sinemet CR, Stalevo, Vyalev) include a warning about the risk of vitamin B6 (pyridoxine) deficiency and vitamin B6 deficiency-related seizures associated with their use. The combination of carbidopa/levodopa is the most effective treatment for the motor symptoms of Parkinson's disease and recent evidence favors its early use.

The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems. No disease-modifying drugs are available for treatment of PD.

View the Comparison Table: Drugs for Parkinson's Disease

The FDA has approved opicapone (Ongentys – Neurocrine), a peripherally-acting reversible catechol-O-methyltransferase (COMT) inhibitor, for oral use as an adjunct to carbidopa/levodopa in adults with Parkinson’s disease (PD) who experience "off" episodes. It is the third COMT inhibitor to be approved for this indication; tolcapone (Tasmar, and generics) and entacapone (Comtan, and generics) were approved earlier. Opicapone has been available in Europe since 2016.

The FDA has approved istradefylline (Nourianz — Kyowa Kirin), an oral adenosine A_2A receptor antagonist, for use as an adjunct to carbidopa/levodopa in adults with Parkinson's disease (PD) who experience "off" episodes. Istradefylline is the first adenosine A_2A receptor antagonist to be approved in the US; it has been available in Japan since 2013.

The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems.

View the Comparison Table: Drugs for Parkinson's Disease

The FDA has approved a new formulation of carbidopa/levodopa (Rytary – Impax) in extended-release capsules for treatment of Parkinson’s disease (PD).

Parkinson’s disease (PD) is caused primarily by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat PD because it does not cross the blood-brain barrier.

ParkinsonÆs disease (PD) is caused primarily by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat PD because it does not cross the bloodbrain barrier.

Parkinson's disease is caused by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat Parkinson's disease because it does not cross the blood-brain barrier.

Levodopa combined with carbidopa (Sinemet, and others) is the most widely used treatment for patients with Parkinson's disease, but after 2 to 5 years most patients develop troublesome complications (Treatment Guidelines from The Medical Letter 2004; 2:41). The newest treatment for Parkinson's disease patients with end-of-dose "wearing-off" is Stalevo (Novartis), a combination of the catechol-O-methyltransferase (COMT) inhibitor entacapone (Comtan) with 3 different doses of levodopa/carbidopa. The rationale for Stalevo is that it permits some patients to take only one pill rather than two.