HPLC Analytical Method Development and Validation of Gabapentin through Chemical Derivatization with Catechol as a Chromophore

Background

Gabapentin is a drug with anticonvulsant activity and has been widely used in the treatment of epilepsy. Gabapentin chemical structure lacks a chromophore which makes its absorption very low and hence complicates its analysis and reduces the sensitivity of the method. Adding a chromophore by chemical derivatization makes the drug easily identified and quantified at a much lower concentration using chromatographic analysis such as HPLC. Methodology. The derivatization of gabapentin was done by adding a chromophore to the structure by introducing an auxochrome group. Suitable coupling reagents were used to introduce catechol group to gabapentin. The analytical method has been developed using HPLC with UV/Vis detector. Moreover, the method was validated for parameters such as linearity, range, precision, accuracy, LOD, and LOQ.

Result

The developed method adapted derivatization of gabapentin using catechol reagent measured at λmax 300 nm. The method used HPLC using mobile phase methanol water 50 : 50. The eluted peak of the derivatized gabapentin was separated from other used derivatization reagents. The analytical method showed to be a validated method, and all the tested validation parameters were within the accepted limits. The developed method was found to be linear (R² = 0.9917), precise (RSD = 0.91) and accurate (% recovery = 105). Moreover, the developed method was sensitive with LOD (0.5^∗10⁻⁶ mg/mL) and LOQ (1.5^∗10⁻⁶ mg/mL).

Conclusion

The developed method is simple and feasible with high sensitivity and selectivity. It can be applied in the analysis of gabapentin in different dosage forms and raw materials including active pharmaceutical ingredients (API). This research work can be continued in the future, and the developed method can be used for testing gabapentin in biological systems.

Doping detection in animals: A review of analytical methodologies published from 1990 to 2019

Despite the impressive innate physical abilities of horses, camels, greyhounds, or pigeons, doping agents might be administered to these animals to improve their performance. To control these illegal practices, anti-doping analytical methodologies have been developed. This review compiles the analytical methods that have been published for the detection of prohibited substances administered to animals involved in sports over 30 years. Relevant papers meeting the search criteria that discussed analytical methods aiming to detect and/or quantify doping substances in animal biological matrices published from 1990 to 2019 were considered. A total of 317 studies were included, of which 298 were related to horses, demonstrating significant advances toward the development of doping detection methods for equine sports. However, analytical methods for the detection of doping agents in sports involving other species are lacking. Due to enhanced accuracy and specificity, chromatographic analysis coupled to mass spectrometry detection is preferred over immunoassays. Regarding biological matrices, blood and urine remain the first choice, although alternative biological matrices, such as hair and feces, have been considered. With the increasing number and type of drugs used as doping agents, the analytes addressed in the published papers are diverse. It is very important to continue to detect and quantify these drugs, recognizing those that are most frequently used, in order to punish the abusers, protect animals' health, and ensure a healthier and genuine competition.

Characterization of an Amphetamine Interference from Gabapentin in an LC-HRMS Method

An amphetamine interference was observed during the development of an liquid chromatography-high-resolution mass spectrometry (LC-HRMS) multi-class confirmation method for the determination of 47 drugs and metabolites in urine. The interference passed all qualitative criteria for amphetamine leading to potential false-positive results. Upon investigation, it was found that the amphetamine interference was correlated with the presence of high levels of gabapentin. Gabapentin is routinely detected in patient urine specimens at levels in excess of 1 mg/mL as it is widely prescribed at high doses and does not undergo significant metabolism. The source of the interference was identified as a gabapentin in-source fragment isomeric with protonated amphetamine. Here we describe the characterization of this interference and how its effect was mitigated in the LC-HRMS method.

Spectroscopic Methods for Quantifying Gabapentin: Framing the Methods without Derivatization and Application to Different Pharmaceutical Formulations

This work aimed at analyzing the performance of direct spectroscopic methods for the quantification of gabapentin (GABAp), given the lack of previous studies, in comparison with the more reviewed and complex derivatization techniques, discussing their susceptibility to the pharmaceutical formulations. All of the methods analyzed showed high selectivity for this pharmaceutical analyte, with recoveries close to 100%. Absorption spectroscopy without derivatization yielded better sensitivity and lower limits of detection and quantification of gabapentin in aqueous solution (AqSol method) when compared with other solvents, such as acidic solution or ethanol/water mixture. Derivatization with sodium hypochlorite presented the highest precision, whereas derivatization with vanillin exhibited the highest accuracy. The best method for GABAp quantification in terms of highest sensitivity, lowest limits of detection, and quantification, and also with good precision and accuracy, proved to be fluorescence with derivatization by 4-chloro-7-nitrobenzofurazan. The effect of the pharmaceutical formulation (nature of excipients) was tested for the most robust and sensitive methods, with and without derivatization, on capsules of five commercial brands. Recoveries in the range of 97.9-101.5% proved that there are no matrix interfering effects. Although not presenting the best performance in all the parameters evaluated, the AqSol method, due to its simplicity, proved to be suitable for the quantification of GABAp in capsules and tables containing the molecule as the active ingredient.

Gas chromatography-electron ionization-mass spectrometry quantitation of valproic acid and gabapentin, using dried plasma spots, for therapeutic drug monitoring in in-home medical care

A simple and sensitive gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) method using dried plasma spot testing cards was developed for determination of valproic acid and gabapentin concentrations in human plasma from patients receiving in-home medical care. We have proposed that a simple, easy and dry sampling method is suitable for in-home medical patients for therapeutic drug monitoring. Therefore, in the present study, we used recently developed commercially available easy handling cards: Whatman FTA DMPK-A and Bond Elut DMS. In-home medical care patients can collect plasma using these simple kits. The spots of plasma on the cards were extracted into methanol and then evaporated to dryness. The residues were trimethylsilylated using N-methyl-N-trimethylsilyltrifluoroacetamide. For GC-EI-MS analysis, the calibration curves on both cards were linear from 10 to 200 µg/mL for valproic acid, and from 0.5 to 10 µg/mL for gabapentin. Intra- and interday precisions in plasma were both ≤13.0% (coefficient of variation), and the accuracy was between 87.9 and 112% for both cards within the calibration curves. The limits of quantification were 10 µg/mL for valproic acid and 0.5 µg/mL for gabapentin on both cards. We believe that the present method will be useful for in-home medical care.