Nano-scale multi-spectroscopic analysis of the anti-fibromyalgia drug pregabalin based on dihydropyridine ring formation with sustainability and whiteness evaluation

This research addresses the challenge of analyzing pregabalin, a primary amine in a zwitterionic structure, which is difficult to evaluate due to its lack of chromatophore. The study introduces a derivatization assessment using Hantzsch's multicomponent organic reaction to enhance the detectability of pregabalin by forming a highly fluorescent dihydropyridine derivative. This process involves the condensation of pregabalin with acetylacetone and formaldehyde, yielding a yellowish-green compound measurable both colorimetrically at 338 nm and fluorimetrically at an emission wavelength of 486 nm (λexcitation = 408 nm). The reaction conditions were thoroughly optimized to obtain the highest possible sensitivity, reduce reagent and time consumption, and use safe solvents. The developed method displayed high sensitivity and linearity in the concentration ranges of 4.0 - 20.0 µg/mL in colorimetric assay and reached a nano-scale analysis level of 40 - 2000 ng/mL with a detection limit down to 10 ng/mL when adopting the fluorimetric measurement. Both assessments were rigorously evaluated for their performance, adhering to the International Conference on Harmonization (ICH) standards. The accuracy of these methods was confirmed through the recovery rates of real samples, showing 98.9 ± 0.2 % for colorimetric and 98.2 ± 0.7 % for fluorimetric assessment. The excellent sensitivity of the suggested spectrofluorometric approach led to its use in the measurement of PRG in spiked human urine samples, resulting in particularly good recoveries ranging from 95.3 to 102.8 %. Meanwhile, the Need, Quality, Sustainability (NQS) index looks into how necessary the method is, execution quality (evaluated using the RGB 12 algorithm), and how it fits with the Sustainable Development Goals (SDGs), underlining the benefits of employing natural reagents. The developed approach showed superiority in sensitivity and sustainability compared to previous analytical approaches for pregabalin.

Chemometrically Assisted Optimization of Pregabalin Fluorescent Derivatization Reaction with a Novel Xanthone Analogue and Validation of the Method for the Determination of Pregabalin in Bulk via a Plate Reader

Quantitation of chromophore-free analytes is always a challenge. To this purpose, derivatization of the analyte constitutes a common strategy, leading to a product with a strong signal. In the current study, a novel xanthone analogue was utilized for the first time for the derivatization of pregabalin, a model analyte with a primary amine moiety that lacks a chromophore. The fact that only the xanthene-based derivative, formed after the derivatization reaction fluoresces, enables avoiding its chromatographic separation from the reagent and thus reducing the analysis time of a series of samples in 1–2 min via a plate reader. The reaction conditions were optimized via a central composite design (CCD), with fluorescence signal as the measure of the yield. The following factors that affect the derivatization reaction were chosen: (a) temperature, (b) reaction time, and (c) triethylamine solution volume used to drive the reaction to completion. After the identification of the optimal conditions, the method was validated according to ICH guidelines, using a fluorescence plate reader for signal measurement (λex = 540, λem = 615 nm). Finally, the newly developed high-throughput method was applied to the determination of drug content in pregabalin bulk.

Enantiomeric Identification of Pregabalin by GC-MS via Methylation and S-TPC Chiral Derivatization

Pregabalin is a Schedule V controlled substance which is defined as the (S) enantiomer of 3-(aminomethyl)-5-methylhexanoic acid. It is used legitimately to treat neuropathy in patients with diabetes as well as for epilepsy and fibromyalgia. Pregabalin is an amino acid and an amphoteric compound, which makes it difficult to analyze using the conventional GC-MS instrumentation found in most forensic drug analysis laboratories. Problems associated with the traditional GC-MS analysis of pregabalin include selective solubility, ring closure to the corresponding lactam in the GC injection port and/or the MS transfer line and difficulty with chiral derivatization due to the presence of a carboxylic acid moiety. Here, we show that these challenges can be overcome by methylating (capping) the carboxylic acid portion of the pregabalin molecule and converting to the corresponding methyl ester. Once the methyl ester is synthesized, chiral derivatization at the amine can be achieved to identify the controlled (S) enantiomer of pregabalin via GC-MS.

Kinetic spectrophotometric determination of an important pharmaceutical compound, pregabalin

Background

Pregabalin (PGB), an anticonvulsant, was studied throughout this work using spectrophotometric method.

Methods

The spectrophotometric method is based on the condensation reaction of PGB with p-dimethylaminobenzaldehyde (p DMAB) in acid medium. The condensation product showed λ max at 420 nm.

Results

The different parameters affecting the stability of the condensation product were carefully studied and optimized. The calibration plots were constructed over the concentration range of 40 to 120 μg ml-1.

Conclusions

A simple, reliable, sensitive and accurate spectrophotometric method has been developed for the determination of an anticonvulsant drug, PGB. The proposed method was successfully applied to the analysis of the drug in dosage form. The high sensitivity of the proposed method allows determination of PGB in bulk and in pharmaceutical preparations.

Development and validation of sensitive spectrophotometric method for determination of two antiepileptics in pharmaceutical formulations

Rapid, sensitive and validated spectrophotometric methods for the determination of two antiepileptics (gabapentin (GAB) and pregabalin (PRG)) in pure forms and in pharmaceutical formulations was developed. The method is based on the formation of charge transfer complex between drug and the chromogenic reagents quinalizarin (Quinz) and alizarin red S (ARS) producing charge transfer complexes in methanolic medium which showed an absorption maximum at 571 and 528 nm for GAB and 572 and 538 nm for PRG using Quinz and ARS, respectively. The optimization of the reaction conditions such as the type of solvent, reagent concentration and reaction time were investigated. Beer's law is obeyed in the concentration ranges 0.4-8.0 and 0.5-10 μg mL(-1) for GAB and PRG using Quinz and ARS, respectively. The molar absorptivity, Sandell sensitivity, detection and quantification limits are also calculated. The correlation coefficients were ≥0.9992 with a relative standard deviation (RSD%) of ≤1.76. The methods are successfully applied to the determination of GAB and PRG in pharmaceutical formulations and the validity assesses by applying the standard addition technique, which compared with those obtained using the reported methods.

Utility of certain nucleophilic aromatic substitution reactions for the assay of pregabalin in capsules

BACKGROUND

Pregabalin (PG) is an anticonvulsant, analgesic and anxiolytic drug. A survey of the literature reveals that all the reported spectrophotometric methods are either don't offer high sensitivity, need tedious extraction procedures, recommend the measurement of absorbance in the near UV region where interference most probably occurs and/or use non specific reagent that don't offer suitable linearity range.

RESULTS

Two new sensitive and simple spectrophotometric methods were developed for determination of pregabalin (PG) in capsules. Method (I) is based on the reaction of PG with 1,2-naphthoquinone-4-sulphonate sodium (NQS), yielding an orange colored product that was measured at 473 nm. Method (II) is based on the reaction of the drug with 2,4-dinitrofluorobenzene (DNFB) producing a yellow product measured at 373 nm. The different experimental parameters affecting the development and stability of the reaction product in methods (I) and (II) were carefully studied and optimized. The absorbance-concentration plots were rectilinear over the concentration ranges of 2-25 and 0.5-8 μg mL-1 for methods (I) and (II) respectively. The lower detection limits (LOD) were 0.15 and 0.13 μg mL-1 and the lower quantitation limits (LOQ) were 0.46 and 0.4 μg mL-1 for methods (I) and (II) respectively.

CONCLUSION

The developed methods were successfully applied to the analysis of the drug in its commercial capsules. The mean percentage recoveries of PG in its capsule were 99.11 ± 0.98 and 100.11 ± 1.2 (n = 3). Statistical analysis of the results revealed good agreement with those given by the comparison method. Proposals of the reaction pathways were postulated.