Carbidopa is a peripherally-restricted inhibitor of dopamine decarboxylase, the enzyme that converts L-DOPA to dopamine.¹Carbidopa (100 mg/kg) pretreatment in dog increases the plasma concentration of L-DOPA by 186% and prolongs the half-life in plasma by 48% and skeletal muscle extracellular fluid by 66%.²Carbidopa also binds to and potentiates the activity of the aryl hydrocarbon receptor (AhR), which is a ligand-dependent transcription factor that mediates the toxicity of certain xenobiotics and polyaromatic hydrocarbons.³It inhibits the proliferation of pancreatic cancer cellsin vitroand tumor growthin vivo. Formulations containing carbidopa are used in combination with L-DOPA in the treatment of Parkinson's disease to increase the amount of dopamine in the brain and reduce peripheral side effects associated with L-DOPA administration.

1.Clark, W.G., Oldendorf, W.H., and Dewhurst, W.G.Blood-brain barrier to carbidopa (MK -486) and Ro 4-4602, peripheral dopa decarboxylase inhibitorsJ. Pharm. Pharmacol.25(5)416-418(1973) 2.Deleu, D., Sarre, S., Ebinger, G., et al.The effect of carbidopa on the pharmacokinetics and metabolism of intravenously administered levodopa in blood plasma and skeletal muscleNaunyn Schmiedebergs Arch. Pharmacol.348(6)576-581(1993) 3.Ogura, J., Miyauchi, S., Shimono, K., et al.Carbidopa is an activator of aryl hydrocarbon receptor with potential for cancer therapyBiochem J.474(20)3391-3402(2017)