HPLC-UV method development for fentanyl determination in rat plasma and its application to elucidate pharmacokinetic behavior after i.p. administration to rats

Hepatic and renal toxicities and metabolism of fentanyl analogues in rats

New synthetic opioids continue to emerge in the illicit market, and among them, fentanyl analogues pose a serious threat to the public health with their abuse and trafficking. We investigated the toxicity of fentanyl analogues on the liver and kidneys mediated by the µ-opioid receptor (MOR). Our study focused on 4-fluoro-isobutyrylfentanyl (4F-iBF), which is classified as a "narcotic" in Japan; structurally similar analogues 4-chloro-isobutyrylfentanyl (4Cl-iBF) and isobutyrylfentanyl (iBF) were also investigated. Rats that were intraperitoneally administered 4F-iBF (5 mg/kg (12.3 μmol/kg)) or iBF (12.3 μmol/kg) displayed hepatic and renal ischemic-like damage, but 4Cl-iBF (12.3 μmol/kg) did milder renal damage only. We found that the agonist activity of 4F-iBF, at MORs was approximately 7.2 times that of 4Cl-iBF, and that pretreatment with MOR antagonist naltrexone (0.8 mg/kg) alleviated liver and kidney injuries caused by 4F-iBF. These results suggested that 4F-iBF might cause ischemic damage to the liver and kidneys, induced by respiratory depression mediated by MORs. Furthermore, to elucidate the metabolism of fentanyl analogues, we investigated the change over time in the amount of 4F-iBF, 4Cl-iBF, iBF (6.15 μmol/kg, respectively), and their respective metabolites in serum after intraperitoneal administration to rats. The results showed that in 24-h post-dose serum, 4Cl-iBF and iBF were substantially eliminated while 4F-iBF remained at about 30% of the maximum level, and each of the N-dephenylethylated metabolites of 4F-iBF, 4Cl-iBF, and iBF was detected in 2-h post-dose serum. The results from this study revealed information on the hepatic and renal toxicities and metabolism related to fentanyl analogues.

Fentanyl but Not Morphine or Buprenorphine Improves the Severity of Necrotizing Acute Pancreatitis in Rats

Opioids are widely used for the pain management of acute pancreatitis (AP), but their impact on disease progression is unclear. Therefore, our aim was to study the effects of clinically relevant opioids on the severity of experimental AP. Various doses of fentanyl, morphine, or buprenorphine were administered as pre- and/or post-treatments in rats. Necrotizing AP was induced by the intraperitoneal injection of L-ornithine-HCl or intra-ductal injection of Na-taurocholate, while intraperitoneal caerulein administration caused edematous AP. Disease severity was determined by laboratory and histological measurements. Mu opioid receptor (MOR) expression and function was assessed in control and AP animals. MOR was expressed in both the pancreas and brain. The pancreatic expression and function of MOR were reduced in AP. Fentanyl post-treatment reduced necrotizing AP severity, whereas pre-treatment exacerbated it. Fentanyl did not affect the outcome of edematous AP. Morphine decreased vacuolization in edematous AP, while buprenorphine pre-treatment increased pancreatic edema during AP. The overall effects of morphine on disease severity were negligible. In conclusion, the type, dosing, administration route, and timing of opioid treatment can influence the effects of opioids on AP severity. Fentanyl post-treatment proved to be beneficial in AP. Clinical studies are needed to determine which opioids are best in AP.

Lipemia in the Plasma Sample Affects Fentanyl Measurements by Means of HPLC-MS2 after Liquid-Liquid Extraction

Examination of fentanyl levels is frequently performed in certain scientific evaluations and forensic toxicology. It often involves the collection of very variable blood samples, including lipemic plasma or serum. To date, many works have reported the methods for fentanyl detection, but none of them have provided information about the impact on the assay performance caused by an excessive amount of lipids. This aspect may be, however, very important for highly lipophilic drugs like fentanyl. To address this issue, we developed the liquid chromatography method with mass spectrometry detection and utilized it to investigate the impact of lipids presence in rabbit plasma on the analytical method performance and validation. The validation procedure, conducted for normal plasma and lipemic plasma separately, resulted in good selectivity, sensitivity and linearity. The limits of detection and quantification were comparable between the two matrices, being slightly lower in normal plasma (0.005 and 0.015 µg/L) than in lipemic plasma (0.008 and 0.020 µg/L). Liquid–liquid extraction provided a low matrix effect regardless of the lipid levels in the samples (<10%), but pronounced differences were found in the recovery and accuracy. In the normal plasma, this parameter was stable and high (around 100%), but in the lipemic matrix, much more variable and less efficient results were obtained. Nevertheless, this difference had no impact on repeatability and reproducibility. In the present work, we provided reliable, convenient and sensitive method for fentanyl detection in the normal and lipemic rabbit plasma. However, construction of two separate validation curves was necessary to provide adequate results since the liquid-liquid extraction was utilized. Therefore, special attention should be paid during fentanyl quantification that involves lipemic plasma samples purified by this technique.

Quantitative determination of fentanyl in newborn pig plasma and cerebrospinal fluid samples by HPLC-MS/MS

In this study, a selective and sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method requiring low sample volume (≤100 μL) was developed and validated for the quantitative determination of the opioid drug fentanyl in plasma and cerebrospinal fluid (CSF). A protein precipitation extraction with acetonitrile was used for plasma samples whereas CSF samples were injected directly on the HPLC column. Fentanyl and (13) C6 -fentanyl (Internal Standard) were analyzed in an electrospray ionization source in positive mode, with multiple reaction monitoring (MRM) of the transitions m/z 337.0/188.0 and m/z 337.0/105.0 for quantification and confirmation of fentanyl, and m/z 343.0/188.0 for (13) C6 -fentanyl. The respective lowest limits of quantification for plasma and CSF were 0.2 and 0.25 ng/mL. Intra- and inter-assay precision and accuracy did not exceed 15%, in accordance with bioanalytical validation guidelines. The described analytical method was proven to be robust and was successfully applied to the determination of fentanyl in plasma and CSF samples from a pharmacokinetic and pharmacodynamic study in newborn piglets receiving intravenous fentanyl (5 µg/kg bolus immediately followed by a 90-min infusion of 3 µg/kg/h).

Recent advances in hydrophilic interaction chromatography for quantitative analysis of endogenous and pharmaceutical compounds in plasma samples

There is an increasing need for new analytical methods that can handle a large number of analytes in complex matrices. Hydrophilic interaction chromatography (HILIC) has recently been demonstrated as an important supplement to reversed-phase liquid chromatography for polar analytes, particularly endogenous compounds. With the increasing popularity of HILIC, progressively more polar phases with diverse functional groups have been developed. In addition, the coupling of HILIC to mass spectrometry offers the advantages of improved sensitivity by employing an organic-rich mobile phase. This article reviews recent applications of HILIC for the analysis of endogenous and pharmaceutical compounds in plasma samples. Furthermore, based on recent studies, we provide a discussion of column selection, sample pretreatment for HILIC analysis, and detection sensitivity.

A simple liquid chromatography-tandem mass spectrometry method for determination of plasma fentanyl concentration in rats and patients with cancer pain

A fentanyl patch is widely used for the treatment of cancer pain. Its few adverse effects include constipation and drowsiness. The absorption volume of transdermally applied fentanyl may differ according to its site of application and variability in patch adhesion. Since fentanyl is predominantly metabolized by the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 in the liver, its concentration may vary in cases of physiologically reduced CYP3A4 activity in the liver (liver disease and aging) or on co-administration of drugs. The clinical significance of measuring plasma concentration of fentanyl is high, but conventional methods require complicated processes such as solid-phase extraction and liquid-liquid extraction before the sample is injected into an HPLC system. In this study, a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for determining plasma fentanyl concentrations by deproteinization with acetonitrile. A recovery test was conducted using an absolute calibration curve to confirm the method's linearity and inter- and intra-day reproducibility. The required plasma volume for detection was reduced from 1 mL in the conventional method to 20 µL in the present study, and a good calibration curve was obtained in the concentration range from 0.05 to 5 ng/mL. These findings suggest that the method for sample preparation and quantification developed in this study are appropriate for measuring fentanyl concentration in human plasma in clinical settings.