Effect of the anticoagulant ethylenediamine tetra-acetic acid (EDTA) on the estimation of pharmacokinetic parameters: A case study with tigecycline and ciprofloxacin

Simultaneous quantification of baloxavir marboxil and its active metabolite in human plasma using UHPLC-MS/MS: Application to a human pharmacokinetic study with different anticoagulants

Baloxavir marboxil (BXM) is a cap-dependent nucleic acid endonuclease inhibitor, which exerts its antiviral effects after being metabolized to its active form baloxavir acid (BXA). Ethylenediamine tetra-acetic acid (EDTA) and heparin are the two most used anticoagulants in clinical blood sample collection to estimate drug levels in plasma. However, compared to heparin plasma, there is a lack of clinical pharmacokinetic data of BXA using EDTA anticoagulant tubes for blood collection. In the present study, an efficient, rapid, and sensitive ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for simultaneous quantification of BXM and its active metabolite BXA in human plasma with its isotopic baloxavir-d5 (BXA-d5) as internal standard (IS). Plasma samples (50 μL) were undergone using acetonitrile containing 0.1 % formic acid a precipitant. Chromatographic separation was achieved by a Waters XBridge®C8 (2.1 mm × 50 mm, 2.5 µm) column. The gradient mobile phase was 0.1 % formic acid in water (A, pH 2.8) and 0.1 % formic acid in acetonitrile (B) and delivered at a flow rate of 0.6 mL/min for 4.5 min. BXM and BXA were monitored using a positive electrospray triple quadrupole mass spectrometer (TRIPLE QUAD™ 6500+) via multiple reaction monitoring mode. The mass-to-charge ratios (m/z) were 572.2→247.0, 484.2→247.0 and 489.2→252.0 for BXM, BXA, and BXA-d5 (IS). Calibration curves exhibited excellent linearity in the range of 0.1-10 ng/mL for BXM (r2 > 0.996), and 0.3-300 ng/mL for BXA (r2 > 0.998). Within-run and between-run precisions in coefficients of variations were less than 11.62 % for BXM and less than 7.47 % for BXA, and accuracies in relative error were determined to be within -7.78 % to 5.70 % for BXM and -6.67 % to 8.56 % for BXA. Extraction recovery efficiency was 92.76 % for BXM, 95.32 % for BXA, and 99.26 % for BXA-d5, respectively. The matrix effect of BXM and BXA was in line with the requirements, where the relative deviation of the accuracy was less than 6.67 % and the precision was less than 6.69 %. The validated efficient and simple UHPLC-MS/MS method was successfully used in the pharmacokinetic study of BXM and BXA in healthy human volunteers with K2EDTA and heparin tubes for blood collection. EDTA might compete with BXA for chelating metal ions and thereby decrease the plasma ratio in whole blood, leading to approximately 50 % lower measurement of pharmacokinetic parameters as compared with those obtained from heparin plasma anticoagulant tubes.

Impact of Experimental Variables on the Protein Binding of Tigecycline in Human Plasma as Determined by Ultrafiltration

Tigecycline, a tetracycline derivative, shows atypical plasma protein binding behavior. The unbound fraction decreases with increasing concentration at therapeutic concentrations. Moreover, uncertainty exists about the magnitude of tigecyline's protein binding in man. Unbound fractions between 2.5% and 35% have been reported in plasma from healthy volunteers, and between 25% and 100% in patients, respectively. In the present study, the protein binding of tigecycline has been investigated by ultrafiltration using different experimental conditions. Whereas temperature had only a marginal influence, the unbound fraction at 0.3/3.0 mg/L was low at pH 8.2 (9.4%/1.9%) or in unbuffered pooled plasma (6.3%/1.2%), compared with plasma buffered with HEPES to pH 7.4 (65.9%/39.7%). In experiments with phosphate buffer and EDTA, the concentration dependency was markedly attenuated or abolished, which is compatible with a cooperative binding mechanism involving divalent cations such as calcium. The unbound fraction in clinical plasma samples from patients treated with tigecycline was determined to 66.3 ± 13.7% at concentrations <0.3 mg/L compared with 41.3 ± 16.0% at >1 to <5 mg/L. To summarize, tigecycline appears to be only moderately bound to plasma proteins as determined by ultrafiltration, when a physiological pH is maintained.

Decreased protein binding of moxifloxacin in patients with sepsis?

The mean (SD) unbound fraction of moxifloxacin in plasma from patients with severe sepsis or septic shock was determined by ultrafiltration to 85.5±3.0% (range 81.9 and 91.6%) indicating a decreased protein binding of moxifloxacin in this population compared with the value of 58-60% provided in the Summary of Product Characteristics. However, previous investigations neglected the influence of pH and temperature on the protein binding of moxifloxacin. Maintaining physiological conditions (pH 7.4, 37°C) - as in the present study - the unbound fraction of moxifloxacin in plasma from healthy volunteers was 84%. In contrast, the unbound fraction of moxifloxacin was 77% at 4°C and 66-68% in unbuffered plasma or at pH 8.5 in fair agreement with previously published data. PK/PD parameters e.g. fAUC/MIC or ratios between interstitial fluid and free plasma concentrations, which were obtained assuming a protein binding rate of moxifloxacin of 40% or more, should be revised.

Effect of various anticoagulants on the bioanalysis of drugs in rat blood: implication for pharmacokinetic studies of anticancer drugs

BACKGROUND

Pharmacokinetic studies are vital in development and optimization of drugs. While blood samples can be collected either in EDTA, heparin or citrate containing tubes for the estimation of drug levels in plasma, EDTA tubes are more commonly used. The purpose of this study was to evaluate the effects of anticoagulants on bioanalysis of drugs. Six drugs used extensively in cancer therapy were selected. Albino wistar rats (N = 6 per drug) were dosed with one of the following drugs intraperitoneally-pemetrexed (50 mg/kg), imatinib (50 mg/kg), erlotinib (25 mg/kg), meropenem (60 mg/kg), 6-mercaptopurine (20 mg/kg) and voriconazole (6 mg/kg). Blood samples were collected 2 h after dosing (1 h in 6-mercaptopurine group due to short half-life) by terminal bleeding from the retro-orbital plexus. Blood was collected in each of Disodium ETDA, heparin, trisodium citrate (TSC) and no anticoagulant (plain) tubes. Drug levels in these samples were determined by validated HPLC assays. ANOVA with Tukey's post hoc test was performed to identify statistically significant differences in drug concentrations in anticoagulant tubes. p < 0.05 was considered statistically significant.

RESULTS

Significant differences in concentration between anticoagulant tubes was observed in case of erlotinib (p = 0.013) and meropenem (p = 0.00), while borderline statistical significance for pemetrexed (p = 0.076). TSC tubes overestimated erlotinib levels, heparin tubes underestimated meropenem concentrations and EDTA tubes overestimated pemetrexed concentrations.

CONCLUSIONS

Careful selection of anti-coagulant is necessary for accurate characterization of pharmacokinetics of drugs. Routine use of EDTA tubes may lead to erroneous interpretation of pharmacokinetic data.

Role of Divalent Metal Ions in Atypical Nonlinear Plasma Protein Binding Behavior of Tigecycline

In typical nonlinear plasma protein binding (PPB) behavior, the free fraction increases with increasing total concentrations. In contrast, when a drug exhibits atypical nonlinear PPB behavior, the free fraction decreases with increasing total concentrations. Tigecycline, a novel glycylcycline, exhibits atypical nonlinear PPB behavior, but the mechanism of such behavior is currently unknown. Because tigecycline can form complexes with metal ions, an interaction between metal ion, tigecycline, and plasma proteins was hypothesized but not further investigated. The current work explores the role of metal ions in the atypical nonlinear PPB behavior of tigecycline and proposes a plausible mechanism of atypical nonlinear PPB behavior. The addition of ethylenediaminetetraacetic acid resulted in 10- to 30-fold higher unbound fractions, and the atypical behavior was nullified. The saturation of ethylenediaminetetraacetic acid chelation, by addition of excessive divalent metal ions, such as calcium and magnesium, led to the return of the atypical nonlinear PPB behavior. Different possible mechanisms were evaluated by simulation, and a plausible mechanism was proposed.

The therapeutic effect of tigecycline, unlike that of Ceftazidime, is not influenced by whether the Klebsiella pneumoniae strain produces extended-spectrum β-lactamases in experimental pneumonia in rats

The efficacies of tigecycline and ceftazidime against fatal pneumonia in rats caused by an extended-spectrum β-lactamase (ESBL)-positive Klebsiella pneumoniae strain or its wild-type (WT) progenitor were compared. Ceftazidime at 12.5 or 50 mg/kg of body weight twice daily (b.i.d.) was effective (50% or 100% rat survival) in pneumonia caused by the WT isolate but unsuccessful (100% rat mortality) in pneumonia caused by the ESBL-positive variant. In contrast, tigecycline at 6.25, 12.5, or 25 mg/kg b.i.d. showed dosage-dependent efficacy up to 100% rat survival irrespective of the ESBL character of the infecting organism.

Novel in vitro-in vivo extrapolation (IVIVE) method to predict hepatic organ clearance in rat

PURPOSE

Drug elimination in the liver consists of uptake, metabolism, biliary excretion, and sinusoidal efflux from the hepatocytes to the blood. We aimed to establish an accurate prediction method for liver clearance in rats, considering these four elimination processes. In vitro assays were combined to achieve improved predictions.

METHODS

In vitro clearances for uptake, metabolism, biliary excretion and sinusoidal efflux were determined for 13 selected compounds with various physicochemical and pharmacokinetic properties. Suspended hepatocytes, liver microsomes and sandwich-cultured hepatocytes were evaluated as in vitro models. Based on the individual processes, in vivo hepatic clearance was calculated. Subsequently, the predicted clearances were compared with the corresponding in vivo values from literature.

RESULTS

Using this in vitro-in vivo extrapolation method good linear correlation was observed between predicted and reported clearances. Linear regression analysis revealed much improved prediction for the novel method (r(2) = 0.928) as compared to parameter analysis using hepatocyte uptake only (r(2) = 0.600), microsomal metabolism only (r(2) = 0.687) or overall hepatobiliary excretion in sandwich-cultured hepatocytes (r(2) = 0.321).

CONCLUSIONS

In this new attempt to predict hepatic elimination under consideration of multiple clearance processes, in vivo hepatic clearances of 13 compounds in rats were well predicted using an IVIVE analysis method based on in vitro assays.