Graham Lawson

Pharmacokinetics of Midazolam in Neonates Undergoing Extracorporeal Membrane Oxygenation

Background Although the pharmacokinetics of midazolam in critically ill children has been described, there are no such reports in extracorporeal membrane oxygenation. Methods The pharmacokinetics of midazolam and 1-hydroxy midazolam after continuous infusion (50–250 &mgr;g · kg−1 · h−1) were determined in 20 neonates undergoing extracorporeal membrane oxygenation. Patients were randomized into two groups: group 1 (n = 10) received midazolam extracorporeally (into the circuit), and group 2 received drug via central or peripheral access. Blood samples for determination of plasma concentrations were taken at baseline, 2, 4, 6, 12, 18, and 24 h, then every 12 h. Population pharmacokinetic analysis and model building was conducted using WinNonMix (Pharsight Corporation, Mountain View, CA). The 1-hydroxy midazolam/midazolam metabolic ratio was determined as a surrogate marker of cytochrome P450 3A activity. Results The parameter estimates (n = 19) were based on a one-compartment model with time-dependent change in volume of distribution. Volume (mean ± standard error) expanded monoexponentially from the onset of extracorporeal membrane oxygenation to a maximum value, 0.8 l ± 0.5 and 4.1 ± 0.5 l/kg, respectively. Consequently, plasma half-life was substantially prolonged (median [range]) from onset to steady-state: 6.8 (2.2–39.8) and 33.3 (7.4–178) h, respectively. Total body clearance was determined as (mean ± standard error) 1.4 ± 0.15 ml · kg−1 · min−1. The median metabolic ratio was 0.17 (0.03–0.9). No significant differences were observed between the two groups with respect to parameter estimates. Simulations of plasma concentration profiles revealed excess levels at conventional doses. Conclusions These results reveal significantly increased volume of distribution and plasma half-life in neonates receiving extracorporeal membrane oxygenation. Altered kinetics may reflect sequestration of midazolam by components of the extracorporeal membrane oxygenation circuit.

Dexamethasone quantification in dried blood spot samples using LC–MS: The potential for application to neonatal pharmacokinetic studies

A high-performance liquid chromatography (LC-MS) method has been developed and validated for the determination of dexamethasone in dried blood spot (DBS) samples. For the preparation of DBS samples whole blood spiked with analyte was used to produce 30μl blood spots on specimen collection cards. An 8mm disc was cut from the DBS sample and extracted using a combination of methanol: water (70:30, v/v) containing the internal standard, triamcinolone acetonide. Extracts were centrifuged and chromatographic separation was achieved using a Zorbax Eclipse Plus C18 column using gradient elution with a mobile phase of acetonitrile and water with formic acid at a flow rate of 0.2ml/min. LC-MS detection was conducted with single ion monitoring using target ions at m/z 393.1 for dexamethasone and 435.1 for the internal standard. The developed method was linear within the tested calibration range of 15-800ng/ml. The overall extraction recovery of dexamethasone from DBS samples was 99.3% (94.3-105.7%). The accuracy (relative error) and precision (coefficient of variation) values were within the pre-defined limits of ≤15% at all concentrations. Factors with potential to affect drug quantification measurements such as blood haematocrit, the volume of blood applied onto the collection card and spotting device were investigated. Although a haematocrit related effect was apparent, the assay accuracy and precision values remained within the 15% variability limit with fluctuations in haematocrit of ±5%. Variations in the volume of blood spotted did not appear to affect the performance of the developed assay. Similar observations were made regarding the spotting device used. The methodology has been applied to determine levels of dexamethasone in DBS samples collected from premature neonates. The measured concentrations were successfully evaluated using a simple 1-compartment pharmacokinetic model. Requiring only a microvolume (30μl) blood sample for analysis, the developed assay is particularly suited to pharmacokinetic studies involving paediatric populations.

Analytical methods used in conjunction with dried blood spots.

This review covers the wide range of different methods that have been used for the microanalysis of dried blood spots (DBS) from the ones reported in 1914 to the sophisticated processes used, for example, in newborn screening, new drug discovery research and application of PCR based DNA studies of HIV in countries with limited infrastructure. The value of the dried blood spot as a sampling tool and the many advantages it offers in combination with suitable analytical methods is discussed. Current developments in both automating the DBS extraction process and the potential for direct analysis of the sample without prior extraction are reviewed. Possible future directions in the analytical methods used for DBS samples are also highlighted.

Quantitative determination of atenolol in dried blood spot samples by LC–HRMS: A potential method for assessing medication adherence

The use of blood spot collection cards was investigated as a means of obtaining small volume samples for the quantification of therapeutic drugs for assessing medication adherence. A liquid chromatography-high resolution TOF mass spectrometry (LC-HRMS) method, based on the measurement at the accurate mass to charge ratio of the target analyte, was used to ensure specificity for atenolol in the dried blood spot (DBS) samples. A working method was developed and validated. For the preparation of DBS samples whole blood spiked with analyte was used to produce 30 μl blood spots on specimen collection cards. A 5mm disc was cut from the dried blood spot and extracted using methanol:water (60:40, v/v) containing the internal standard, atenolol-d(7). Extracts were vortexed, sonicated and then centrifuged. Gradient chromatographic elution was achieved using an Ascentis Express C18 100mm×2.1mm column and a mobile phase flow rate of 0.2 ml/min and the column oven temperature at 30 °C. MS detection was carried out in electrospray positive ion mode for target ions at accurate mass m/z 267.1703 for atenolol and 274.2143 for the IS. Drug extraction efficiency from spiked blood spots was demonstrated to be 96±5% and the drug was stable in DBS for at least 10 weeks. The developed LC-HRMS method was linear within the tested calibration range of 25-1500 ng/ml and validation showed the accuracy (relative error) and precision (coefficient of variation) values were within the pre-defined limits of ≤ 5% at all concentrations with a limit of quantification of 25 ng/ml. Factors with potential to affect drug quantification measurements such as the matrix effects, volume of blood applied onto the collection card and effect of different sampling cards were investigated. The developed LC-HRMS method was applied to blood spots on sampling card taken from adult healthy volunteers previously administered a 50mg atenolol tablet and a DBS concentration-time profile was obtained for atenolol. Requiring only a micro volume (30 μl) blood sample for analysis, the developed DBS based assay has the potential to assess patient adherence to atenolol.

Plasma concentrations of midazolam in neonates receiving extracorporeal membrane oxygenation

Drug disposition is affected during extracorporeal membrane oxygenation (ECMO). This study investigates the dose-concentration relationship of midazolam in neonates requiring ECMO during continuous infusion into the circuit (extracorporeally; n = 10) and intravenously (n = 10). Data on hourly doses and sedation scores were collected for 120 hours. Plasma concentrations were analyzed at times 0, 2, 4, 6, 12, 18, and 24, and every 12 hours thereafter. Both groups were clinically similar. Mean (standard deviation) dose for all patients was 250 (185) &mgr;g/kg/h, four times greater than previously reported. Doses administered in the first 24 hours were significantly greater extracorporeally [361 (300)] compared with intravenous [258 (190) &mgr;g/kg/h, p < 0.001]. Mean (standard deviation) plasma concentrations in all patients at 24, 48, and 72 hours were 1.4 (0.9), 1.8 (1.2), and 2.6 (1.8) &mgr;g/ml, respectively. Satisfactory sedation levels were achieved in all patients. Comparison of the actual observed with predicted (simulated) midazolam concentrations suggested significant attenuation of plasma levels during the first 24 hours of ECMO. However, at 48 hours, observed concentrations exceeded those predicted, suggesting accumulation. We conclude that in the first 24 hours of ECMO, because of an expanded circulating volume and sequestration by the circuit, significantly more midazolam is required to achieve adequate sedation. Subsequently, and because of circuit saturation, maintenance doses should be reduced.

Bisoprolol, ramipril and simvastatin determination in dried blood spot samples using LC-HRMS for assessing medication adherence.

The use of dried blood spot (DBS) collection cards was investigated for the quantification of three therapeutic drugs used in cardiovascular therapy for assessing medication adherence. A liquid chromatography-high resolution mass spectrometry (LC-HRMS) method was developed and validated for the determination of bisoprolol, ramipril and simvastatin. Whole blood spiked with target analytes was used to produce 30 μl blood spots on specimen collection cards. An 8mm disc was cut from the dried blood spot and extracted using methanol: water (70:30, v/v) containing the internal standard, atenolol. Extracts were vortexed, sonicated and then centrifuged. Gradient chromatographic elution was achieved using a Zorbax Eclipse C18 HD 100 mm × 2.1 mm, 1.8 μm pore size column and a mobile phase flow rate of 0.6 ml/min and the column oven temperature at 40 °C with a run time of 3 min. MS detection was carried out in electrospray positive ion mode for the three target drugs and for the IS. Drug recoveries from spiked blood spots were ≥ 92% for bisoprolol and ramipril and ~43% for simvastatin and the drugs were stable in DBS for at least 12 weeks. Validation of the LC-HRMS method showed good linearity and the accuracy (relative error) and precision (coefficient of variation) values were within the pre-defined limits of ≤ 15% at all concentrations. Matrix effects and the effects of different volumes of blood applied to the collection card were investigated. The LC-HRMS method successfully identified control volunteers who were known to be either adherent or non-adherent. There were no false positives from volunteers taking other cardiovascular drugs or from volunteers receiving no medication.

Electrospray Mass Spectrometry: An Alternative Method for the Identification of Organotin Compounds

The limitations of conventional gas chromatography-mass spectrometry (GC-MS) analyses for alkyl- and aryl-tin compounds are discussed, particularly the excessive fragmentation from electron impact (EI) ionization. Negative EI methods exhibit low ionization capabilities and are restricted to compounds with an electronegative centre, and are thus not suitable for general routine analysis. Liquid chromatography-MS (LC-MS) interfaces offer potential advantages in terms of reduced sample work-up since no derivatization is required. Electrospray techniques give reproducible mass spectra for each compound studied under fixed instrumental parameters. Changes in the cone/repeller voltages can radically alter the observed mass spectra. High-mass species were observed for each compound studied and tentative structures for these species are proposed.

Effects of neonatal extracorporeal membrane oxygenation circuits on drug disposition

Abstract Background: It has been observed that neonatal patients receiving extracorporeal membrane oxygenation (ECMO) require larger doses of sedatives than do non-ECMO patients to achieve similar levels of sedation. Objective: The purpose of this study was to determine whether drug disposition of midazolam and morphine, 2 commonly used sedatives, are affected by the ECMO circuit. Methods: This was a 3-part study. First, a retrospective analysis of prescription charts for 10 ECMO neonates and 10 neonates who had undergone cardiac surgery was conducted to confirm that the former group required larger doses of sedatives. Second, uptake of midazolam and morphine by the polyvinylchloride (PVC) and silicone components of the neonatal ECMO circuits was evaluated in vitro. Third, known concentrations of midazolam were injected into a complete neonatal ECMO circuit and analyzed after the oxygenator to determine the effects of the circuit components on the bioavailability of midazolam. Results: Mean ± SD total dose of midazolam for the ECMO neonates was 21,283 ± 10,446 μg versus 9599 ± 5504 μg for the cardiac surgery group ( P = 0.008). Mean ± SD total dose of morphine for the ECMO neonates was 2364 ± 1280 μg versus 1158 ± 457 μg for the cardiac surgery group ( P = 0.017). There was significant uptake (68%) of midazolam by the PVC and silicone components of neonatal ECMO circuits, whereas morphine uptake of 16% was observed only during contact with the PVC component. After 40 minutes of running a new ECMO circuit, the concentration of midazolam leaving the circuit was Conclusions: There is significant interaction between the PVC and silicone components of an ECMO circuit and the sedative drugs that pass through them. These interactions may affect the bioavailability of these drugs and hence the doses required to induce a therapeutic effect.

Dried blood spot analysis to assess medication adherence and to inform personalization of treatment

Little research using dried blood spot samples to assess adherence to medication has been reported. The World Health Organisation estimates that only half of the patients in the developed world take their medication as prescribed. Additional costs to the healthcare provider include wasted medicines, avoidable additional hospital visits and non-optimum patient care. There is little evidence of information concerning medication adherence being made available to inform clinical decision making. In this article we explore the potential of the dried blood spot sample collection methodology as a means of identifying medication adherence to facilitate medicines optimization for a range of disparate diseases. Furthermore, the opportunity to personalize healthcare for different patients by assessing the clinically necessary therapeutic level of the relevant drugs is highlighted.

MALDI-MS and colorimetric analysis of diisocyanate and polyol migrants from model polyurethane adhesives used in food packaging

The identification of the migrants, into food simulants, from a series of polyurethane adhesives used in the manufacture of plastic film laminates for use in common food packaging is described. Commercial materials, based on four different model adhesive systems, were prepared by an industrial collaborator. The MALDI-MS fingerprint patterns of the three polyether and one polyester polyol components of these adhesives were obtained for reference purposes. The decrease in the level of diisocyanate as a migrant versus time after lamination was confirmed by colorimetric measurements. The migration of the standard polyol samples through polyethylene pouches into water at 70 degrees C has been demonstrated and also the attenuation effect for different polyols. Cured laminates in the form of pouches were used to carry out the migration experiments into distilled water, inside the pouch, at 70 degrees C over a period of 2 h. Comparison of the migration results from the food packaging laminates with those from the polyethylene film confirmed the migration of unreacted polyol components for the polyether-based systems. Cyclic oligomers from the polyol starting materials were identified as the migrants from the polyester-based adhesive.