This reduces the side effects caused by dopamine on the periphery, as well as increasing the concentration of L-DOPA and dopamine in the brain. The combination of carbidopa/levodopa carries the brand names of Kinson, Sinemet, Pharmacopa and Atamet; while Stalevo is a combination with entacapone, which enhances the bioavailability of carbidopa and levodopa. Carbidopa is most commonly used as a method to inhibit the activity of dopamine decarboxylase. This is an enzyme that breaks down L-Dopa in the periphery and converts it to dopamine. This results in the newly formed dopamine being unable to cross the blood–brain barrier and the effectiveness of L-Dopa treatments is greatly decreased. Carbidopa reduces the amount of levodopa required to produce a given response by about 75% and, when administered with levodopa, increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid. Elimination half-life of levodopa in the presence of carbidopa is about 1.5 hours. Following SINEMET CR, the apparent half-life of levodopa may be prolonged because of continuous absorption. This is extremely useful in the treatment of Parkinsons disease symptoms because the amount of levodopa administered to the patient can be greatly reduced. This reduction in dosage is extremely useful due to the side effects that may occur from an overdose of L-Dopa within the body. Carbidopa is also used in combination with 5-HTP, a naturally occurring amino acid which is a precursor to the neurotransmitter serotonin and an intermediate in tryptophan metabolism. carbidopa, which is used in PD to prevent conversion of the levodopa to dopamine, prevents 5-Hydroxytryptophan’s (5-HTP) metabolism in the liver and causes decreased levels of serotonin in the blood. Research shows that co-administration of 5-HTP and carbidopa greatly increases plasma 5-HTP levels. Several cases of scleroderma-like illness have been reported in patients using carbidopa and 5-HTP. In Europe, 5-HTP is prescribed with carbidopa to prevent the conversion of 5-HTP into serotonin until it reaches the brain. Synthesis The synthesis begins with a modified Strecker reaction using hydrazine and potassium cyanide on arylacetone (1) to give 2. This is then hydrolyzed with cold HCl to give carboxamide 3. More vigorous hydrolysis with 48% HBr cleaves the amide bond and the aryl ether group to produce carbidopa (4). References External links Lodosyn prescribing information Sinemet datasheet for New Zealand Catecholamines Hydrazines Aromatic L-amino acid decarboxylase inhibitors Antiparkinsonian agents Peripherally selective drugs