GC/MS determination of gabapentin in human plasma and vitreous humor and its application to forensic samples

Gabapentin (GBP) is widely prescribed off-label, and cases of misuse, abuse, self-medication, and intentional self-harm have been reported. This study aimed to develop and validate a simple GC-MS method for the determination of GBP in plasma and vitreous humor (VH) and to explore the relationship between concentrations in both matrices in postmortem cases. An SPE procedure was evaluated, and the selected cartridge was used with an extraction procedure adapted from a previously published method. Derivatization was not required, resulting in reduced reagent consumption and a shorter analytical procedure. The method was validated according to FDA guidelines. The calibration ranges were 2.5-15.0 μg/mL for plasma and 1.0-10.0 μg/mL for VH. The method was applied to nine postmortem cases. Plasma GBP concentrations in six intoxication cases ranged from 3.26 to 52.76 μg/mL (mean, 16.1 μg/mL), whereas concentrations in cases in which GBP was considered incidental ranged from 2.47 to 11.44 μg/mL (mean, 7.3 μg/mL). Except for one case, VH concentrations were lower than plasma concentrations. The GBP_plasma/GBP_VH ratio ranged from 1.5 to 2.7 (mean, 1.9) when the case with a higher VH concentration was excluded. The limited number of cases and potential postmortem factors preclude definitive conclusions regarding the relationship between plasma and VH concentrations. Further studies are warranted to assess VH as an alternative matrix when blood is unavailable.