Search

In this paper is reported the selective colorimetric detection and quantification of carbidopa, an inhibitor of aromatic amino acid decarboxylase, in the co-presence of levodopa as dopamine precursor in pharmaceutical formulations for the treatment of Parkinson's disease. The method is based on the selective condensation reaction between the hydrazine group from carbidopa and the formyl functional group of vanillin, a natural flavoring agent, in acidified alcoholic solution. The yellow color development (λ max  ~ 420 nm) due to the formation of 4-hydroxy-3-methoxybenzaldazine (HMOB) was observed for carbidopa only, whereas levodopa, lacking the hydrazine group, did not color the solution, as expected. The calibration curves for two tablet formulations of levodopa in combination with carbidopa (4:1) were superimposable with levodopa/carbidopa (4:1), as well as carbidopa alone, in standard solution, i.e., the excipients and additives did not interfere with carbidopa determination, corresponding to a mean recovery about 105%. The linear dynamic range was between 5.00 and 50.0 mg L -1 with very good reproducibility within this range (CV av % about 3-4%) and very good sensitivity, with limits of quantification of about 1 mg L -1 . The colorimetric method developed here is very simple, inexpensive, and effective for drug estimation and quality control of pharmaceutical formulations., (© 2022. The Author(s).)

In this paper is reported the selective detection and quantification of levodopa in co-presence of carbidopa. The method took advantage of the spontaneous oxidation and color development of levodopa at basic pH here driven by alkaline earth cations and co-solvent in solution. We have shown for the first time the generation and stabilization of the purple melanochrome from levodopa, by using magnesium acetate and dimethyl sulfoxide, which was here exploited for the development of a quantitative colorimetric assay for the active principle ingredient in commercial drugs for the treatment of Parkinson's disease. The calibration curves of levodopa in the two tablet formulations, containing carbidopa as decarboxylase inhibitor, showed a common linear trend between 10 mg L -1 and 40 mg L -1 with levodopa alone or in combination with carbidopa in standard solutions, with very good reproducibility (CV av %, 3.3% for both brand and generic drug) and very good sensitivity, with limit of quantification about 0.6 mg L -1 in any case. The colorimetric method here developed is very simple and effective, appearing as a rapid and low-cost alternative to other methodologies, involving large and expensive instrumentations, for drug estimation and quality control of pharmaceutical formulations., (© 2021. Springer-Verlag GmbH Germany, part of Springer Nature.)

The quality of life of patients affected by Parkinson's disease is improved by medications containing levodopa and carbidopa, restoring the dopamine concentration in the brain. Accordingly, the affordable quality control of such pharmaceuticals is very important. Here is reported the simple and inexpensive colorimetric quantification of carbidopa in anti-Parkinson drugs by the selective condensation reaction between the hydrazine group from carbidopa and the formyl functional group of selected aldehydes in acidified hydroalcoholic solution. An optical assay was developed by using indole-3-carbaldehyde (I3A) giving a yellow aldazine in EtOH:H2O 1:1 (λmax~415 nm) at 70 °C for 4 h, as confirmed by LC-MS analysis. A filter-based plate reader was used for colorimetric data acquisition, providing superior results in terms of analytical performances for I3A, with a sensitivity ~50 L g−1 and LOD ~0.1 mg L−1 in comparison to a previous study based on vanillin, giving, for the same figures of merit values, about 13 L g−1 and 0.2–0.3 mg L−1, respectively. The calibration curves for the standard solution and drugs were almost superimposable, therefore excluding interference from the excipients and additives, with very good reproducibility (avRSD% 2–4%) within the linear dynamic range (10 mg L−1–50 mg L−1). [ABSTRACT FROM AUTHOR]

We used the first enzyme-free synthesis and stabilization of soluble melanochrome (MC) and 5,6-indolequinone (IQ) derived from levodopa (LD), dopamine (DA), and norepinephrine (NE) oxidation to develop a simple colorimetric assay for catecholamine detection in human urine, also elucidating the time-dependent formation and molecular weight of MC and IQ using UV–Vis spectroscopy and mass spectrometry. The quantitative detection of LD and DA was achieved in human urine using MC as a selective colorimetric reporter to demonstrate the potential assay applicability in a matrix of interest in therapeutic drug monitoring (TDM) and in clinical chemistry. The assay showed a linear dynamic range between 5.0 mg L−1 and 50.0 mg L−1, covering the concentration range of DA and LD found in urine samples from, e.g., Parkinson's patients undergoing LD-based pharmacological therapy. The data reproducibility in the real matrix was very good within this concentration range (RSDav% 3.7% and 6.1% for DA and LD, respectively), also showing very good analytical performances with the limits of detection of 3.69 ± 0.17 mg L−1 and 2.51 ± 0.08 mg L−1 for DA and LD, respectively, thus paving the way for the effective and non-invasive monitoring of dopamine and levodopa in urine from patients during TDM in Parkinson's disease. [ABSTRACT FROM AUTHOR]