Abstract
Objective: Fast disintegrating tablets (FDTs) are found helpful in dysphagia (difficulty in swallowing) especially in Parkinson patients. Levodopa is still the first choice in Parkinson disease treatment and is co-administered by carbidopa for better efficacy.
 Methods: In the present study, a rapid and simple isocratic Reverse Phase-High Performance Liquid Chromatography (RP-HPLC) method was developed and validated for simultaneous quantification of levodopa and carbidopa in optimized Fast Disintegrating Tablets (FDTs). The linearity, precision, accuracy, limit of detection (LOD) and limit of quantification (LOQ) of the method were determined. FDTs were prepared using direct compression, dry and wet granulation and were optimized for faster disintegration time. Tablets thickness, weight, hardness, friability, drug content and dissolution profile were also evaluated.
 Results: A RP-HPLC system with C18 column and mobile phase 90:10 (v/v) phosphate buffer: methanol was used. The method linearity was found to be within the concentration range of 3.125-50 μg/ml for levodopa, and 3.125-25 μg/ml for carbidopa. The intra and inter-day precision and accuracy were acceptable. LOD and LOQ of levodopa-carbidopa were 0.2-0.8 μg/ml and 0.5-2.4 μg/ml, respectively. The total chromatographic run time was 5 min. The optimized FDTs hardness was 3.81±0.4 and tablets were disintegrated within 30 sec. Levodopa and carbidopa were dissolved in dissolution media within 5 min.
 Conclusion: Results indicated that this method was suitable for simultaneous quantification of levodopa and carbidopa in the presence of different ingredients of a pharmaceutical solid dosage form. Therefore, this method could be applied in pharmaceutical quality control for rapid quantification of structurally similar substances with different physicochemical properties.
Highlights
Parkinson is a neurodegenerative disease affects dopaminergic neurons within the nigro-striatal and surrounding pathways which decreases dopamine in the central nervous system [1]
To prevent levodopa peripheral degradation and increase its concentration in the systemic circulation, levodopa is coadministered with carbidopa which is a peripheral amino acid decarboxylase inhibitor [3]
high performance liquid chromatography (HPLC) apparatus equipped with UV/Vis detector was used for levodopa and carbidopa
Summary
Parkinson is a neurodegenerative disease affects dopaminergic neurons within the nigro-striatal and surrounding pathways which decreases dopamine in the central nervous system [1]. Considering extensive metabolism in the peripheral circulation, levodopa exhibits low oral bioavailability and brain uptake. The first levodopa-carbidopa marketed product was a conventional swallowing tablet [2]. The most preferred route of administration for drug therapy is an oral route. Solid oral dosage forms such as tablets must be swallowed to release their active ingredient in gastrointestinal fluids for absorption [4, 5]. Pediatric and geriatric patients have difficulty in swallowing the conventional dosage forms [6,7,8]. Dysphagia (difficulties in swallowing) which is more prevalent in Parkinson's disease [9], results in poor compliance in many of the elderly patients who use the conventional tablets [10]
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