Dried blood spot liquid chromatography assay for therapeutic drug monitoring of metformin

The use of blood spot collection cards is a simple way to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in routine clinical setting. We describe the development and validation of a microanalytical technique for the determination of metformin from dried blood spots. The method is based on reversed phase high-performance liquid chromatography with ultraviolet detection. Drug recovery in the developed method was found to be more than 84%. The limits of detection and quantification were calculated to be to be 90 and 150 ng/ml, respectively. The intraday and interday precision (measured by CV%) was always less than 9%. The accuracy (measured by relative error, %) was always less than 12%. Stability analysis showed that metformin is stable for at least 2 months when stored at -70 degrees C. The small volume of blood required (10 mu L), combined with the simplicity of the analytical technique makes this a useful procedure for monitoring metformin concentrations in routine clinical settings. The method is currently being applied to the analysis of blood spots taken from diabetic patients to assess adherence to medications and relationship between metformin level and metabolic control of diabetes. (c) 2006 Elsevier B.V. All rights reserved.

Development and validation of a dried blood spot-LC-APCI-MS assay for estimation of canrenone in paediatric samples

A selective and sensitive liquid chromatography (LC)-atmospheric pressure chemical ionisation (APCI)-mass spectroscopic (MS) assay of canrenone has been developed and validated employing Dried Blood Spots (DBS) as the sample collection medium. DBS samples were prepared by applying 30 mu l of spiked whole blood onto Guthrie cards. A 6 mm disc was punched from the each DBS and extracted with 2 ml of methanolic solution of 17 alpha-methyltestosterone (Internal Standard). The methanolic extract was evaporated to dryness and reconstituted in acetonitrile:water (1:9, v/v). The reconstituted solution was further subjected to solid phase extraction using HLB cartridges. Chromatographic separation was achieved using Waters Sunfire C18 reversed-phase column using isocratic elution, followed by a high organic wash to clear late eluting/highly retained components. The mobile phase consisted of methanol:water (60:40, v/v) pumped at a flow rate of 0.3 ml/min. LC-APCI-MS detection was performed in the selected-ion monitoring (SIM) mode using target ions at m/z 341.1 and 303.3 for canrenone and internal standard respectively. The selectivity of the method was established by analysing DBS samples from 6 different sources (individuals). The calibration curve for canrenone was found to be linear over 25-1000 ng/ml (r >0.994). Accuracy (% RE) and precision (% CV) values for within and between day were

Wavelength Dependence of Raman Enhancement from Gold Nanorod Arrays: Quantitative Experiment and Modeling of a Hot Spot Dominated System

Surface-enhanced Raman scattering (SERS) spectra from molecules adsorbed on the surface of vertically aligned gold nanorod arrays exhibit a variation in enhancement factor (EF) as a function of excitation wavelength that displays little correlation with the elastic optical properties of the surface. The key to understanding this lack of correlation and to obtaining agreement between experimental and calculated EF spectra lies with consideration of randomly distributed, sub-10 nm gaps between nanorods forming the substrate. Intense fields in these enhancement “hot spots” make a dominant contribution to the Raman scattering and have a very different spectral profile to that of the elastic optical response. Detailed modeling of the electric field enhancement at both excitation and scattering wavelengths was used to quantitatively predict both the spectral profile and the magnitude of the observed EF.

Metronidazole Population Pharmacokinetics in Preterm Neonates Using Dried Blood-Spot Sampling

OBJECTIVES: To characterize the population pharmacokinetics of metronidazole in preterm neonates.
PATIENTS AND METHODS: Data were collected prospectively from 32 preterm neonates who received intravenous metronidazole for the treatment of or prophylaxis against necrotizing enterocolitis. Dried
blood spots (n 203) on ?lter paper were analyzed by highperformance liquid chromatography, and the data were subjected to pharmacokinetic analysis performed by using nonlinear mixed-effect modeling.
RESULTS: A 1-compartment model best described the data. Signi?cant covariates were weight (WT) and postmenstrual age (PMA). The ?nal population models for metronidazole clearance (CL) and volume of distribution (V) were: CL 0.0247 (WT/1.00)0.75 (1 0.107 [PMA 30]) and V 0.726 WT, where CL is in liters per hour, WT is in kilograms, PMA is in weeks, and V is in liters. This model predicts that the half-life of metronidazole decreases rapidly from 40 hours at 25 weeks’ PMA to 19 hours at 32 weeks’ PMA, after which it starts to plateau. This decrease in half-life is the result of a 5-fold increase in CL compared with only a 2.5-fold increase in V during the same period.
CONCLUSIONS: Currently, there are no speci?c dose recommendations for metronidazole in preterm neonates. However, a dosing scheme for preterm neonates that takes into consideration both the weight and PMA has been suggested and should avoid administration of doses that are excessive or more frequent than necessary.

Development and validation of a dried blood spot LC-MS/MS assay to quantify ranitidine in paediatric samples.

A novel approach has been developed to determine ranitidine in paediatric samples using dried blood spots (DBS) on Guthrie cards (Whatman 903). A selective and sensitive HPLC-MS/MS assay has been developed and validated using small volumes of blood (30µl). A 6mm disc was punched from each DBS and extracted with methanolic solution of the internal standard (IS) nizatidine. This was further subjected to solid phase extraction (SPE), followed by reversed phase HPLC separation, using a XBridge™ C18 column and mobile phase 10mM ammonium acetate/methanol (98:2 v/v) with a flow rate of 0.3mL/min. This was combined with multiple reaction monitoring (MRM) mass detection using electrospray ionisation (ESI). The calibration curve for ranitidine was found linear over the range 10-500ng/mL (r=0.996). The limit of quantification (LOQ) of the method was validated at 10ng/mL. Accuracy and precision values for within and between days were

Roche tomography of cataclysmic variables - V. A high-latitude star-spot on RU Pegasi

We present Roche tomograms of the secondary star in the dwarf nova system RU Pegasi derived from blue and red arm ISIS data taken on the 4.2-m William Herschel Telescope. We have applied the entropy landscape technique to determine the system parameters and obtained component masses of M1 = 1.06 Msun, M2 = 0.96 Msun, an orbital inclination angle of i = 43 degrees, and an optimal systemic velocity of gamma = 7 km/s. These are in good agreement with previously published values. Our Roche tomograms of the secondary star show prominent irradiation of the inner Lagrangian point due to illumination by the disc and/or bright spot, which may have been enhanced as RU Peg was in outburst at the time of our observations.We find that this irradiation pattern is axi-symmetric and confined to regions of the star which have a direct view of the accretion regions. This is in contrast to previous attempts to map RU Peg which suggested that the irradiation pattern was non-symmetric and extended beyond the terminator. We also detect additional inhomogeneities in the surface distribution of stellar atomic absorption that we ascribe to the presence of a large star-spot. This spot is centred at a latitude of about 82 degrees and covers approximately 4 per cent of the total surface area of the secondary. In keeping with the high latitude spots mapped on the cataclysmic variables AE Aqr and BV Cen, the spot on RU Peg also appears slightly shifted towards the trailing hemisphere of the star. Finally, we speculate that early mapping attempts which indicated non-symmetric irradiation patterns which extended beyond the terminator of CV donors could possibly be explained by a superposition of symmetric heating and a large spot.

Polar distribution of ablated atomic material during the pulsed laser deposition of Cu in vacuum: Dependence on focused laser spot size and power density

Experiments have been carried out to investigate the polar distribution of atomic material ablated during the pulsed laser deposition of Cu in vacuum. Data were obtained as functions of focused laser spot size and power density. Thin films were deposited onto flat glass substrates and thickness profiles were transformed into polar atomic flux distributions of the form f(theta)=cos(n) theta. At constant focused laser power density on target, I=4.7+/-0.3X10(8) W/cm(2), polar distributions were found to broaden with a reduction in the focused laser spot size. The polar distribution exponent n varied from 15+/-2 to 7+/-1 for focused laser spot diameter variation from 2.5 to 1.4 mm, respectively, with the laser beam exhibiting a circular aspect on target. With the focused laser spot size held constant at phi=1.8 mm, polar distributions were observed to broaden with a reduction in the focused laser power density on target, with the associated polar distribution exponent n varying from 13+/-1.5 to 8+/-1 for focused laser power density variation from 8.3+/-0.3X10(8) to 2.2+/-0.1X10(8) W/cm(2) respectively. Data were compared with an analytical model available within the literature, which correctly predicts broadening of the polar distribution with a reduction in focused laser spot size and with a reduction in focused laser power density, although the experimentally observed magnitude was greater than that predicted in both cases. (C) 1996 American Institute of Physics.

Third harmonic order imaging as a focal spot diagnostic for high intensity laser-solid interactions

As the state of the art for high power laser systems increases from terawatt to petawatt level and beyond, a crucial parameter for routinely monitoring high intensity performance is laser spot size on a solid target during an intense interaction in the tight focus regime ( 10(19) Wcm(-2) is demonstrated experimentally and shown to provide the basis for an effective focus diagnostic. Importantly, this technique is also shown to allow in-situ diagnosis of focal spot quality achieved after reflection from a double plasma mirror setup for very intense high contrast interactions (> 10(20) Wcm(-2)) an important application for the field of high laser contrast interaction science.