DOPA decarboxylase inhibitor (DDCI) such as carbidopa (medicines containing carbidopa, either alone or in combination with -DOPA, are branded as Lodosyn (Aton Pharma) Sinemet (Merck Sharp & Dohme Limited), Pharmacopa (Jazz Pharmaceuticals), Atamet (UCB), Syndopa and Stalevo (Orion Corporation) or with a benserazide (combination medicines are branded Madopar or Prolopa), to prevent the peripheral synthesis of dopamine from -DOPA). Inbrija (previously known as CVT-301) is an inhaled powder formulation of levodopa indicated for the intermittent treatment of "off episodes" in patients with Parkinson's disease currently taking carbidopa/levodopa. It was approved by the United States Food and Drug Administration on December 21, 2018, and is marketed by Acorda Therapeutics. Coadministration of pyridoxine without a DDCI accelerates the peripheral decarboxylation of -DOPA to such an extent that it negates the effects of -DOPA administration, a phenomenon that historically caused great confusion. In addition, -DOPA, co-administered with a peripheral DDCI, is efficacious for the short-term treatment of restless leg syndrome. The two types of response seen with administration of -DOPA are: The short-duration response is related to the half-life of the drug. The longer-duration response depends on the accumulation of effects over at least two weeks, during which ΔFosB accumulates in nigrostriatal neurons. In the treatment of Parkinson's disease, this response is evident only in early therapy, as the inability of the brain to store dopamine is not yet a concern. Biological role -DOPA is produced from the amino acid -tyrosine by the enzyme tyrosine hydroxylase. -DOPA can act as an -tyrosine mimetic and be incorporated into proteins by mammalian cells in place of L-tyrosine, generating protease-resistant and aggregate-prone proteins in vitro and may contribute to neurotoxicity with chronic -DOPA administration. It is also the precursor for the monoamine or catecholamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). Dopamine is formed by the decarboxylation of -DOPA by aromatic -amino acid decarboxylase (AADC). -DOPA can be directly metabolized by catechol-O-methyl transferase to 3-O-methyldopa, and then further to vanillactic acid. This metabolic pathway is nonexistent in the healthy body, but becomes important after peripheral -DOPA administration in patients with Parkinson's disease or in the rare cases of patients with AADC enzyme deficiency. -Phenylalanine, -tyrosine, and -DOPA are all precursors to the biological pigment melanin. The enzyme tyrosinase catalyzes the oxidation of -DOPA to the reactive intermediate dopaquinone, which reacts further, eventually leading to melanin oligomers. In addition, tyrosinase can convert tyrosine directly to -DOPA in