Aromatic L-amino acid decarboxylase (AADC) is the final enzyme in the biosynthesis of the monoamine neurotransmitters serotonin and dopamine, and dopamine is the precursor for norepinephrine and epinephrine[1]. Carbidopa monohydrate is the monohydrate form of Carbidopa. Carbidopa (CD), a competitive inhibitor of AADC that doesn’t cross the blood-brain barrier, is routinely administered with levodopa (LD) to patients with Parkinson disease (PD) to reduce the peripheral decarboxylation of LD to dopamine[2]. On exposure to other human tumor lines, CD was lethal only to NCI-H146 and NCI-H209 small cell lung carcinoma (SCLC) lines (IC50 = 12 ± 1 μM and 22 ± 5 μM, respectively). CD (100 μM) decreased growth of SK-N-SH neuroblastoma and A204 rhabdomyosarcoma cells[3]. For all patients with cerebrospinal fluid (CSF), AUC (area under the curve) serum CD significantly correlated with percent-labeled CSF HVA (R = 0.786, p = 0.02). In addition, a significantly greater percent-labeled CSF HVA was present in “rapid” as compared to “slow” CD absorbers (Patients were divided into “slow” absorbers (those unable to attain a serum CD level of at least 300 ng/ml within 3 hours after CD administration) and those with more “rapid” absorption (patients obtaining a level of 300 ng/ml or greater within the first 3 hours))[2].
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