Gabapentin Determination in Human Plasma and Capsule by Coupling of Solid Phase Extraction, Derivatization Reaction, and UV-Vis Spectrophotometry

Abstract

Gabapentin is an anticonvulsant widely used in the treatment of epilepsy. No peculiar chromophore is available on the gabapentin moiety for direct analysis by absorption spectrophotometry. A sensitive spectrophotometric method for the determination of gabapentin in bulk, pharmaceutical formulations and human plasma has been developed. In this method, gabapentin directly derivatized with vanillin and analyzed without any extraction in bulk and pharmaceutical dosage form and in plasma samples, it was extracted with a reversed-phase solid-phase extraction (SPE) cartridge followed by derivatization with vanillin. Analysis was performed by a spectrophotometer system. The quantitation limit of gabapentin in human plasma was 0.8 mg/L. The method was linear over the concentration range of 10.0-90.0 mg/L and 0.8-10.0 mg/L for pharmaceutical dosage form and plasma, respectively. The method was precise (relative standard deviation, RSD <1.20%) and accurate (relative mean error <5.5%) for both pharmaceutical dosage form and plasma samples. Mean absolute recoveries were 94.5% for plasma.

Keywords: Derivatization; Gabapentin; Plasma; SPE; Spectrophotometry; Vanillin.

Figure 1

Recommended mechanism for vanillin and gabapentin reaction to produce a chromophore

Figure 2

Effect of temperature on completion of GBP derivatization (absorbance of derivatised GBP in the solution at various temperatures (30 to 70^oC)).

Figure 3

Effect of time on completion of GBP derivatization reaction, (absorbance of derivatised GBP in the solution at different times (30 to 150 min)).

Figure 4

Effect of pH of the reaction medium on completion of GBP derivatization reaction (absorbance of derivatised GBP in the solution at different pHs (5.5 to 9.5)).

Figure 5

Degradation of GBP solution refluxed in acidic and alkaline media (Degradation percent of GBP in acidic (blue line) and alkaline (red line) solutions at 15 to 240 min).