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 Table of Contents  
Year : 2019  |  Volume : 2  |  Issue : 2  |  Page : 28-31

Assessment of blood pregabalin stability at different postmortem durations

1 Department of Forensic Chemistry, Naif Arab University for Security Sciences, Riyadh, Kingdom of Saudi Arabia
2 Department of Clinical Sciences, Faculty of Medicine, Princess Nourah Bint Abdulrahman University, Riyadh, Kingdom of Saudi Arabia; Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Cairo University, Giza, Egypt

Date of Submission22-Jun-2020
Date of Decision22-Jul-2020
Date of Acceptance11-Aug-2020
Date of Web Publication13-Feb-2021

Correspondence Address:
Samah F Ibrahim
Department of Clinical Sciences, Faculty of Medicine, Princess Nourah Bint Abdulrahman University, Riyadh, Kingdom of Saudi Arabia, Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Cairo University, Giza

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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sjfms.sjfms_3_20

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Background: Pregabalin (PRG) has been abused due to its availability and its cheap price. This study is aimed to test the postmortem stability of PRG in blood specimens. Materials and Methods: Ninety-six male rats were divided into four groups, which were given oral doses of PRG: 4 g and 2.5 g/kg for 1 day; 50 mg and 20 mg/kg/day for 21 consecutive days. Antemortem PRG stability was assessed at 4 and 6 h after the last ingested dose, while postmortem stability was assessed at 24 and 48 h after death using gas chromatographymass spectrometry. Results: Our study could detect that -80°C was a storage temperature that could reserve PRG stability in antemortem and postmortem blood samples. The increase in oral PRG dosage was accompanied with a significant increase in blood PRG concentration. Postmortem PRG blood concentrations were decreased in comparison to antemortem concentrations. However, this decrease did not highlight a statistically significant difference in PRG stability (P < 0.05) at the tested storage condition. Conclusion: PRG analysis could be performed in a peripheral blood specimen within 2 days of sampling.

Keywords: Antemortem, forensic toxicology, postmortem blood, pregabalin, stability

How to cite this article:
Almowalad RA, Emara H, Ahmed H, Ibrahim SF. Assessment of blood pregabalin stability at different postmortem durations. Saudi J Forensic Med Sci 2019;2:28-31

How to cite this URL:
Almowalad RA, Emara H, Ahmed H, Ibrahim SF. Assessment of blood pregabalin stability at different postmortem durations. Saudi J Forensic Med Sci [serial online] 2019 [cited 2023 Mar 22];2:28-31. Available from: https://www.sjfms.org/text.asp?2019/2/2/28/309345

  Introduction Top

Pregabalin (PRG) is a gabapentinoid, with great structural similarity to gabapentin. It is commonly used in the treatment of neuropathic pain, partial seizures, and generalized anxiety disorder. However, potential PRG abuse has been described.[1]

It is commonly abused due to its recreational hallucinogenic dissociative effects. PRG misuse seemed to occur orally, but intravenous and rectal self-administration were also reported.[1]

PRG achieves steady state within 24–48 h, has a short half-life (within 4–7 h postingestion), and is excreted unchanged in the urine.[2]

PRG binds to the alpha-2-delta ligands, located at presynaptic endings of neurons. This binding attenuates Ca2+ flux into neurons and blocks the release of neurotransmitters, including the excitatory neurotransmitters, resulting in drowsiness up to coma. Prolonged use can lead to tolerance, which necessitates dose escalation.[2]

PRG can be a possible cause of death, especially when combined with other illicit street drugs.[3] It was reclassified into Class C drug controlled substances from April 2019.[4]

In case of drug intoxication deaths, toxicological forensic investigations are requested to detect the postmortem drug concentration and estimate the amount of drug present at the time of death, or the number of tablets consumed, for this reasons, establishing the identity of certain drug and its ante-mortem and postmortem stability is needed.[5]

This study aimed to assess the stability of orally ingested PRG in antemortem and postmortem femoral blood samples collected from the rat model using Gas chromatographyMass spectrometry (GC-MS) and the relation between them were assessed.

  Materials and Methods Top


PRG and gabapentin (internal standard) were obtained from Pfizer® (Berlin, Germany).

Animals and experimental design

Ninety-six male Sprague Dawley rats weighing 250–300 g were used in the study. They were distributed into 32 cages (3 rats/cage) and kept under standard laboratory conditions; the temperature was 24°C ± 3°C with 40% humidity and allowed free access on food and water provided ad libitum.

The experiment was ethically approved by the Institutional Animal Care and Use Committee, King Saud University.

Experimental protocol

Rats were divided into four groups with 24 animals each. Group A was given oral single dose of PRG (4 g/kg body weight/day). Group B was given oral single dose of PRG (2.5 g/kg body weight/day). Group C was given oral 21 consecutive doses of PRG (50 mg/kg body weight/day). Group D was given oral 21 consecutive doses of PRG (20 mg/kg body weight/day). The 4 g, 2.5 g, 50 mg, and 20 mg/kg animal doses were equivalent to human doses of 600 mg, 400 mg, 8 mg, and 3 mg/kg, respectively,.[6] PRG was administered through a gastric tube once a day.

The animals in each group were divided into four subgroups with six animals each where the femoral blood samples were collected based on a previous animal study of postmortem drug detection[7] at 4 and 6 h after the last ingested dose (at the time of death), 24 and 48 h after the time of death.

At the end of the experiment, all rats were anesthetized using pentobarbital sodium intraperitoneal injection (80 mg/kg) and were sacrificed.

The samples were preserved at -80°C till the assessment time (3 days from sampling) then they were prepared according to Hložek et al.[8] A volume of 100 μL of blood sample (100 mg) was mixed with 200 μL water and 10 μL of gabapentin (Internal standard) then 1.0 ml acetonitrile was added. The resulting denatured protein precipitate was separated by centrifugation 5000 rpm for 5 min. The supernatant layer was transferred to a clean test tube. One hundred μL of 2.5 M sodium hydroxide, 1.0 ml of water, 0.5 ml of ethanol, and 50 μL of pyridine were added to the supernatant sample and mixed for 30 s. Then, 50 μL of ethyl chloroformate (derivatizing reagent) was added and vigorously mixed with the sample by vortex for 2 min. PRG in the samples were extracted with 1.5 ml ethyl acetate by mixing for 3 min and were centrifuged at 5000 rpm for 3 min. The upper organic layer of ethyl acetate was separated and dried under nitrogen. Finally, samples were reconstituted with 100 μL ethyl acetate and transferred to GC-MS vial for the analysis.

The GC-MS analysis was carried out using an Agilent Technologies, model 7890B, Santa Clara, CA, USA) that was equipped with an electronically controlled splitless injection port, Helium as a carrier gas, a full scan detector, selective ion monitoring quantification with 102-quantifier ion (m/z) and 128,142, and 172 qualifier ions (m/z).

A representative gas chromatography PRG chromatogram and calibration curve are presented in [Figure 1],[Figure 2],[Figure 3],[Figure 4].
Figure 1: Total ion chromatogram of pregabalin – Ethyl chloroformate derivatives

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Figure 2: Mass spectrum of pregabalin – Ethyl chloroformate derivatives

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Figure 3: Selective ion monitoring spectrum of pregabalin–Ethyl chloroformate derivatives

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Figure 4: Calibration curve of pregabalin from extracted spiked blood

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Statistical analysis

All values are presented as the mean ± standard deviation (SD). Statistical differences between groups were detected using one-way analysis of variance (SPSS for Windows version 11.0, SPSS Inc., Chicago, IL, USA). Differences in means were considered statistically significant at P = 0.05.

  Results Top

The mean (±SD) antemortem blood PRG concentrations at 4 and 6 h after the last ingested dose are presented in [Figure 5]. When the oral doses were 4 g/kg, 2.5 g/kg, 50 mg/kg, and 20 mg/kg the mean blood PRG levels were 31.7 ± 1.5, 17.5±0.9, 13.5±0.7, and 4.8±.5 μL/ml, respectively (P = 0.05). It is evident that the increase in dosage was accompanied by an increase in PRG concentration in the blood [Figure 5].
Figure 5: Antemortem pregabalin blood levels (μg/ml). *and # statistically significant compared to the corresponding value in Groups A and C, respectively, (P < 0.05)

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Post-mortem PRG blood concentrations at 24 and 48 h after death were decreased in comparison to antemortem concentrations. At 24 h after death and with oral doses 4 g/Kg, 2.5 g/kg, 50 mg/kg, and 20 mg/kg, the mean blood PRG levels were 31.4 ± 3.2, 17.1 ± 0.8, 13.2±0.8, and 4.8 ± 0.5 μL/ml, respectively. While at 48 h after death and with before mentioned oral doses, the mean blood PRG levels were 30.9 ± 2.9, 16.9 ± 0.7, 13 ± 0.8, and 4.6 ± 0.5, respectively. However, this decrease did not show any statistical significance difference (P > 0.05) [Table 1].
Table 1: Post-mortem blood PRG concentrations

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  Discussion Top

Forensic toxicologists are frequently asked to analyze the postmortem samples, for example, blood, urine, and other materials to detect certain drug concentrations and interpret the results in the known drug pharmacology.[9]

Antemortem pharmacological assumptions and interpretations are often invalid after death.[10] For this reason, the stability of PRG in antmortem and post-mortem blood samples was investigated, and the relation between them was assessed.

At storage temperature - 80°C for 3 days after sampling, PRG was detected in antemortem and postmortem blood samples up to 48 h after death.

Blood PRG concentrations of 34.1 ± 0.9 (with range 31–37), 17.8 ± 0.8 (with range 15–20) could be considered as toxic concentrations after 4 h of acute PRG overdose; while the presence of blood PRG concentrations 13.6 ± 1.8 (with range 11–16) and 4.9 ± 1 μg/ml (with range 3.4–6.5) could be considered as toxic concentrations after chronic PRG administration.

Our results showed that with increasing the oral PRG dose, the mean blood PRG concentration significantly increased. We were in agreement with Olesen et al.[11] who reported that PRG absorption is linear and obeys the first-order absorption model, where an increase in dose can result in an increase in serum concentration. Moreover, Hong et al.[12] stated that the PRG absorption rate increased over time.

Priez-Barallon et al.,[13] who detected PRG in postmortem human samples, stated that there is no difference between cardiac and peripheral blood levels, and the blood levels of PRG in intoxicated cases showed higher PRG concentration, between 16.3 and 206.7 mg/L.

Braga and Chidley[14] found that patient's serum concentrations of PRG were 60 and 15 mg/L one and 2 days after ingesting an estimated toxic dose of 11.5 g.

Our results showed that the ante-and postmortem concentration differences increased with early postmortem interval (PMI). However, these differences did not show any statistical significance (P < 0.05). The reason of this result could be due to the stability PRG in these specimens.[15]

This result was consistent with Bockbrader et al.[16] and Zilg et al.[15] They stated that drugs with a low volume of distribution (Vd), for example, PRG with Vd 0.56 L/kg,[17] showed lower drug concentration differences compared to drugs with a high Vd.

In addition, Hilberg et al.,[18] stated that drugs with Vd <4 L/Kg did not show postmortem redistribution phenomenon.

Moreover, Zilg et al.[15] suggested that postmortem blood drug level estimation should be performed during PMI; <50 h after death and that peripheral venous blood should be selected and used for the drug analysis.

  Conclusion Top

PRG is a commonly abused recreational drug and its stability significantly affects the interpretation of data to reach a reliable conclusion.

According to our findings, it would be useful to perform PRG analysis in antemortem and postmortem peripheral blood specimens within 2 days of sampling.


We recommend further analysis of PRG levels from different specimens, for eample, hair, cardiac blood, vitreous at different storage conditions, and longer durations to augment the results of this preliminary study before using it in a forensic context.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Schifano F. Misuse and abuse of pregabalin and gabapentin: Cause for concern? CNS Drugs 2014;28:491-6.  Back to cited text no. 1
Schulze-Bonhage A. Pharmacokinetic and pharmacodynamic profile of pregabalin and its role in the treatment of epilepsy. Expert Opin Drug Metab Toxicol 2013;9:105-15.  Back to cited text no. 2
Aperis G, Paliouras C, Zervos A, Arvanitis A, Alivanis P. The use of pregabalin in the treatment of uraemic pruritus in haemodialysis patients. J Renal Care 2010:36;180-5.  Back to cited text no. 3
Burns C. Pregabalin and gabapentin to be reclassified as class C controlled substances. The Pharmaceutical Journal, October 2018;301:7918, online | DOI: 10.1211/PJ.2018.20205611. Available from: https://www.pharmaceuticaljournal.com/news-and- nalysis/news/pregabalin-and-gabapentin-to-be-reclassified- asclass-c-controlled-substances/20205611.article.[Last Accessed on 2020 Oct 7].  Back to cited text no. 4
CookD, Braithwaite R, Hale K. Estimating antemortem drug concentrations from postmortem blood samples: The influence of postmortem redistribution. J Clini Pathol 2000;53:282-5.  Back to cited text no. 5
Nair AB, Jacob S. A simple practice guide for dose conversion between animals and human. J Basic Clin Pharm 2016;7:27.  Back to cited text no. 6
Castaing N, Titier K, Canal-Raffin M, Moore N, Molimard M. Postmortem redistribution of two antipsychotic drugs, haloperidol and thioridazine, in the rat. J Anal Toxicol 2006;30:419-25.  Back to cited text no. 7
Hložek T, Bursová M, Coufal P, Cabala R. Gabapentin, pregabalin and vigabatrin quantification in human serum by GC–MS after hexyl chloroformate derivatization. J Anal Toxicol 2016;40:749-53.  Back to cited text no. 8
Ferner RE, Norman E. Forensic Pharmacology: Medicines, Mayhem, and Malpractice. USA: Oxford University Press; 1996.  Back to cited text no. 9
Ferner R. Post-mortem clinical pharmacology. Br J Clin Pharmacol 2008;66:430-43.  Back to cited text no. 10
Olesen AE, Olofsen E, Olesen SS, Staahl C, Andresen T, Dahan A, et al. The absorption profile of pregabalin in chronic pancreatitis. Basic Clin Pharm Toxicol 2012;111:385-90.  Back to cited text no. 11
Hong T, Han S, Lee J, Jeon S, Yim DS. Comparison of oral absorption models for pregabalin: Usefulness of transit compartment model. Drug Des Devel Ther 2016;10:3995-4003.  Back to cited text no. 12
Priez-Barallon C, Carlier J, Boyer B, Benslima M, Fanton L, Mazoyer C, et al. Quantification of pregabalin using hydrophilic interaction HPLC-high-resolution MS in postmortem human samples: Eighteen case reports. J Anal Toxicol 2014;38:143-8.  Back to cited text no. 13
Braga A, Chidley K. Self-poisoning with lamotrigine and pregabalin. Anaesthesia 2007;62:524-7.  Back to cited text no. 14
Zilg B, Thelander G, Giebe B, Druid H. Postmortem blood sampling – Comparison of drug concentrations at different sample sites. Forensic Sci Int 2017;278:296-303.  Back to cited text no. 15
Bockbrader HN, Wesche D, Miller R, Chapel S, Janiczek N, Burger P. A comparison of the pharmacokinetics and pharmacodynamics of pregabalin and gabapentin. Clin Pharmacokinet 2010;49:661-9.  Back to cited text no. 16
Kaye AD, Vadivelu N, Urman RD. Substance Abuse: Inpatient and Outpatient Management for Every Clinician. New York Heidelberg Dordrecht London: Springer; 2014.  Back to cited text no. 17
Hilberg T, Ripel A, Slordal L, Bjorneboe A, Morland J. The extent of postmortem drug redistribution in a rat model. J Forensic Sci 1999;44:956-62.  Back to cited text no. 18


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1]


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