Abstract
A novel, accurate, precise, inexpensive, and sensitive spectrophotometric approach is established to assay levodopa (LD) in both bulk drug and its pharmaceutical formulations. The method depends on the reaction of the ternary complex of a mixed-ligand type among LD, nickel(II) (Ni(II)), and 2,3-diaminopyridine (DAP) to form a stable complex of Ni-LD-DAP which is not extractable. The complex showed maximum absorption at 478 nm, with the apparent molar absorptivity of 4.93 × 103 L·mol−1·cm−1 and Sandell’s sensitivity of 0.04 μg·cm−2. Beer’s law is obeyed within the concentration range of 2–58 μg·mL-1, and the regression line equation is as follows: Y = 0.0251X + 0.0045 (R2 = 0.9990; n = 5). The detection limit and quantitation limit are found to be 0.1388 μg·mL−1 and 0.4207 μg·mL−1, respectively. The present study achieved reasonable accuracy (average recovery of 100.17%) and good precision (RSD did not exceed 1.71%). The developed method has been validated according to the current ICH guidelines (2013). The results of pure LD and pharmaceutical preparations using the recommended spectrophotometry are promising.
Highlights
Parkinson’s disease (PD) is a neurodegenerative disorder of the extrapyramidal neuronal system, and the pathogenesis of the disease is due to deterioration of the cerebral dopaminergic pathways and the graduated degradation of dopamine (DA) in the black substance
Not more than 1% of LD can be reached to the central nervous system because the metabolism of LD to DA by peripheral amino acid decarboxylase (AADC) will be outside the brain that releases amounts of DA in the circulatory system, which will exhibit undesirable side effects including vomiting, nausea, and hypotension, so it is necessitated that LD is combined with AADC inhibitors such as carbidopa, which reduces the effects of DA and increases the abundance of LD to the brain, increasing the kinetic benefit of the doses given of LD
Several methods such as HPLC, electrochemistry [9, 10], and spectrophotometry [11, 12] are used to determine LD, despite the diversity of techniques used in the determination, but there are many obstacles (Table 1), for example, the chromatography and techniques connected with it are of high cost in terms of materials and tools used, need to experience in the operation system, sample preparation, and specific conditions in separation, and on the other hand, electrochemical methods are quick to accomplish the analysis, but it displays some errors in the analysis unless it provides a special environment such as the need to clean or polish the electrodes. erefore, spectroscopic methods were used for ease, speed, accuracy, and low cost [13,14,15,16,17,18]
Summary
Parkinson’s disease (PD) is a neurodegenerative disorder of the extrapyramidal neuronal system, and the pathogenesis of the disease is due to deterioration of the cerebral dopaminergic pathways and the graduated degradation of dopamine (DA) in the black substance (substantia nigra). Mobility and control of the skeletal muscle system will be affected and major symptoms in people with PD are shown in the form of tremor, muscle stiffness, bradykinesia, and postural instability. Levodopa (L-3,4-dihydroxyphenylalanine, LD) (Figure 1) is a direct chemical precursor of DA and neurotransmitter modulator and is used as an effective drug to treat PD, it penetrates the blood-brain barrier unlike DA, and it will metabolize as soon as it enters and undergoes a rapid decarboxylation by aromatic L-amino acid decarboxylase (AADC) to give DA [1,2,3,4]. Not more than 1% of LD can be reached to the central nervous system because the metabolism of LD to DA by peripheral AADC will be outside the brain that releases amounts of DA in the circulatory system, which will exhibit undesirable side effects including vomiting, nausea, and hypotension, so it is necessitated that LD is combined with AADC inhibitors such as carbidopa, which reduces the effects of DA and increases the abundance of LD to the brain, increasing the kinetic benefit of the doses given of LD
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