Dried Blood Spot Concentrations Research Articles

Use of dried blood spots for the determination of plasma concentrations of nevirapine and efavirenz

Plasma concentrations are frequently used for therapeutic drug monitoring of antiretroviral drugs. Dried blood spot sampling offers a patient-friendly and easy alternative to plasma sampling. However, dried blood spot concentrations are not necessarily equal to plasma concentrations and therefore the objective of this work was to establish the relationship between nevirapine and efavirenz dried blood spot and plasma concentrations to facilitate clinical implementation of dried blood spot sampling. Paired dried blood spot and plasma samples were obtained from 40 HIV-infected patients on nevirapine and 40 on efavirenz treatment. All samples were analysed using validated HPLC-tandem mass spectrometry methods for the two matrices. Theoretical plasma concentrations were calculated from dried blood spot concentrations using the formula [dried blood spot concentration/(1 - haematocrit)] × fraction bound to plasma proteins = plasma concentration. Linear regression and Bland-Altman analysis were used to compare the two methods. Dried blood spot and plasma concentrations of nevirapine and efavirenz correlated well (r(2) = 0.867 and 0.972, respectively), although efavirenz dried blood spot concentrations were 39.8% (SD 7.1%) lower than plasma concentrations. Theoretical plasma concentrations (using patient-specific haematocrit) of nevirapine and efavirenz were similar to measured plasma concentrations, with a mean difference between the two methods of 0.29 mg/L (SD 1.35 mg/L) and 0.08 mg/L (SD 0.31 mg/L), respectively. Dried blood spot concentrations of nevirapine and efavirenz were equal to plasma concentrations after correction for haematocrit and compound-specific plasma protein binding and can therefore be used in clinical practice.

Application of automated serial blood sampling and dried blood spot technique with liquid chromatography–tandem mass spectrometry for pharmacokinetic studies in mice

The goal of this work was to obtain full pharmacokinetic profiles from individual mice with the use of an automated blood sampling system and dried blood spot (DBS) technique. AMG 517, a potent and selective vanilloid receptor (VR1) antagonist, was dosed to mice (n=3) intravenously and blood samples were collected using the automated blood sampling system with the “no blood waste” method. The collected blood samples were a mixture of 25μL blood and 50μL of heparinized saline solution. Two 15μL aliquots were manually spotted onto a DBS card and dried at room temperature for at least 2h before being stored in zip bags with desiccant. The remaining samples (45μL) were stored at −70°C until analysis. Both the DBS and the whole blood samples (diluted with saline (1:2, v/v)) were extracted and analyzed by liquid chromatography–tandem mass spectrometry. The overall extraction recovery of the analyte from the dried blood spots was determined to be about 90%. The pharmacokinetic parameters calculated using the whole blood or the DBS concentration data were comparable, and were obtained from only 3 mice, whereas conventional sampling and analysis would have required up to 27 mice to achieve the same result. The analyte was shown to be stable in the diluted whole blood (blood:saline 1:2) at room temperature for at least 4h and in the DBS for at least 34 days when stored at room temperature. These results indicated that the automated blood sampling system and DBS collection are promising techniques to obtain full pharmacokinetic profiles from individual mice and reduce the use of animals.

Implementing DBS Methodology for the Determination of Compound A in Monkey Blood: GLP Method Validation and Investigation of the Impact of Blood Spreading on Performance

This article describes validation work for analysis of an Abbott investigational drug (Compound A) in monkey whole blood with dried blood spots (DBS). The impact of DBS spotting volume on analyte concentration was investigated. The quantitation range was between 30.5 and 10,200 ng/ml. Accuracy and precision of quality controls, linearity of calibration curves, matrix effect, selectivity, dilution, recovery and multiple stabilities were evaluated in the validation, and all demonstrated acceptable results. Incurred sample reanalysis was performed with 57 out of 58 samples having a percentage difference (versus the mean value) less than 20%. A linear relationship between the spotting volume and the spot area was drawn. The influence of spotting volume on concentration was discussed. All validation results met good laboratory practice acceptance requirements. Radial spreading of blood on DBS cards can be a factor in DBS concentrations at smaller spotting volumes.

Clinical Evaluation of The Determination of Plasma Concentrations of Darunavir, Etravirine, Raltegravir and Ritonavir in Dried Blood Spot Samples

Measurement of drug levels in plasma is currently the gold standard for pharmacological studies. However, venous sampling is not feasible in some populations (e.g., neonates) or may be difficult in certain situations, such as nonhospital-based settings. Dried blood spots (DBS) can be obtained by a simple fingerprick and the subsequent collection of blood on a filter card, allowing patient-friendly sample collection in non-hospital-based settings. Despite these advantages, thus far no clinical evaluation has been performed for the use of DBS concentrations as surrogates for plasma levels. Our purpose was to clinically evaluate DBS sampling for the determination of plasma concentrations for the novel antiretroviral drugs etravirine, darunavir/ritonavir and raltegravir. DBS concentrations were measured in 11 HIV-infected patients using LC-MS/MS. DBS concentrations were proportional to plasma concentrations. All drug concentrations were higher in DBS than in plasma samples. The plasma:DBS ratio and the respective relative standard error of estimate (RSE) of darunavir, etravirine, raltegravir and ritonavir were 0.632 (4.97% RSE), 0.523 (4.84% RSE), 0.617 (14.9% RSE) and 0.592 (2.99% RSE), respectively. Hematocrit did not explain variability in our study. DBS are reproducibly correlated to plasma levels and can be used for monitoring antiretroviral drug exposure in HIV-infected patients.

Determination of moxifloxacin in dried blood spots using LC–MS/MS and the impact of the hematocrit and blood volume

Moxifloxacin (MFX) is a potential oral agent use in the treatment of multidrug-resistance tuberculosis (MDR-TB). Due to variability in pharmacokinetics and in vitro susceptibility of causative bacteria, therapeutic drug monitoring (TDM) of MFX is recommended. Conventional plasma sampling for TDM is facing logistical challenges, especially in limited resource areas, and dried blood spots (DBS) sampling may offer a chance to overcome this problem. The objective of this study was to develop a LC–MS/MS method for determination of MFX in dried blood spots (DBS) that is applicable for TDM. The influence of paper type, the hematocrit (Hct) and the blood volume per spot ( V b) on the estimated blood volume in a disc ( V est) was investigated. The extracts of 8 mm diameter discs punched out from DBS were analyzed using liquid chromatography tandem mass spectrometry (LC–MS/MS) with cyanoimipramin as internal standard. The method was validated with respect to selectivity, linearity, accuracy, precision, sensitivity, recovery and stability. The effect of Hct and V b on LC–MS/MS analytical result was also investigated. The relationship between MFX concentrations in venous and finger prick DBS and those in plasma was clinically explored. V est was highly influenced by Hct while the effect of V b appeared to be different among paper types. Calibration curves were linear in the range of 0.05–6.00 mg/L with inter-day and intra-day precisions and biases of less than 11.1%. The recovery was 84.5, 85.1 and 92.6% in response to blood concentration of 0.15, 2.50 and 5.00 mg/L, respectively. A matrix effect of less than 11.9% was observed. MFX in DBS was stable for at least 4 weeks at room condition (temperature of 25 °C and humidity of 50%). A large range of Hct value produced a significant analytical bias and it can be corrected with resulting DBS size. A good correlation between DBS and plasma concentrations was observed and comparable results between venous DBS and finger prick DBS was attained. This fully validated method is suitable for determination of MFX in dried blood spot and applicable for TDM.

Ultrafast and high-throughput mass spectrometric assay for therapeutic drug monitoring of antiretroviral drugs in pediatric HIV-1 infection applying dried blood spots

Kaletra® (Abott Laboratories) is a co-formulated medication used in the treatment of HIV-1-infected children, and it contains the two antiretroviral protease inhibitor drugs lopinavir and ritonavir. We validated two new ultrafast and high-throughput mass spectrometric assays to be used for therapeutic drug monitoring of lopinavir and ritonavir concentrations in whole blood and in plasma from HIV-1-infected children. Whole blood was blotted onto dried blood spot (DBS) collecting cards, and plasma was collected simultaneously. DBS collecting cards were extracted by an acetonitrile/water mixture while plasma samples were deproteinized with acetone. Drug concentrations were determined by matrix-assisted laser desorption/ionization-triple quadrupole tandem mass spectrometry (MALDI-QqQ-MS/MS). The application of DBS made it possible to measure lopinavir and ritonavir in whole blood in therapeutically relevant concentrations. The MALDI-QqQ-MS/MS plasma assay was successfully cross-validated with a commonly used high-performance liquid chromatography (HPLC)–ultraviolet (UV) assay for the therapeutic drug monitoring (TDM) of HIV-1-infected patients, and it showed comparable performance characteristics. Observed DBS concentrations showed as well, a good correlation between plasma concentrations obtained by MALDI-QqQ-MS/MS and those obtained by the HPLC-UV assay. Application of DBS for TDM proved to be a good alternative to the normally used plasma screening. Moreover, collection of DBS requires small amounts of whole blood which can be easily performed especially in (very) young children where collection of large whole blood amounts is often not possible. DBS is perfectly suited for TDM of HIV-1-infected children; but nevertheless, DBS can also easily be applied for TDM of patients in areas with limited or no laboratory facilities.

Useful second‐tier tests in expanded newborn screening of isovaleric acidemia and methylmalonic aciduria

Common use of pivalate-generating antibiotics in newborns in Japan and low cutoff value of C5-acylcarnitine (C5) to detect mild forms of isovaleric acidemia (IVA) led to 1,065 positive results from IVA screening among 146,000 newborns tested by tandem mass spectrometry over the last 3 years. Using our method to determine isovalerylglycine (IVG) levels in dried blood spots (DBS) as a second-tier test with IVG cutoff value of 0.5 nmol/ml in DBS, one patient with severe IVA was identified, and no recall of the second DBS was needed. Retrospective analysis revealed that most patients with moderate to severe forms of IVA have decreased free-carnitine levels shortly after birth and higher levels of IVG than those of C5, which suggests that this method is useful in evaluating the severity of IVA. Another second-tier test, to measure methylmalonic acid (MMA) levels in DBS by gas chromatography/mass spectrometry (GC/MS), has been developed to overcome difficulties in screening methylmalonic aciduria (MMAU) and propionic acidemia. Methanol extract from DBS was dried and derivatized using N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide. GC/MS was performed using splitless injection, electron-impact ionization, and selected ion monitoring for data recording. MMAU patients had much higher DBS concentrations of MMA (24.2-321.9 nmol/ml) than control newborns (0.34 ± 0.11 nmol/ml). MMA measurement in DBS was thought to provide useful information about the severity of MMAU, as MMAU patients with high levels of MMA had decreased levels of free carnitine and mildly increased levels of propionylcarnitine.

The utility of neonatal dried blood spots for the assessment of neonatal vitamin D status

Evidence suggests that low concentrations of 25-hydroxyvitamin D(3) (25OHD3) during gestation may be associated with a range of adverse health outcomes in later life. Retrospective estimation of perinatal vitamin D status using questionnaires is extremely unreliable and stored serum samples are rarely available. We aimed to validate the use of dried blood spots (DBS) to estimate perinatal vitamin D status and to determine whether inter-group differences in cord serum 25OHD3 are reflected in DBS. We examined 25OHD3 in 4-year-old frozen cord sera and matched DBS from neonates born at a hospital in Melbourne, Australia (n = 100). We examined the correlation between these values and also investigated whether the expected seasonal (winter/spring vs. summer/autumn) difference in serum 25OHD3 was reflected in DBS values. 25OHD3 was assayed in triplicate using tandem mass spectroscopy in both a 3 microL sample of cord serum and in matched 3 mm punches from archived DBS. 25OHD3 concentrations in neonatal cord serum and DBS were highly correlated (r = 0.85, P < 0.0001). As expected, serum 25OHD3 concentrations were higher in neonates born in summer/autumn (December to March) vs. winter/spring (April to November) (median 46.6 vs. 23.7 nmol/L, P < 0.0001). A comparable difference was seen in DBS values (17.8 vs. 10.5 nmol/L, P = 0.0001). Archived DBS samples provided a valid measure of perinatal vitamin D status and identified inter-seasonal differences in perinatal 25OHD3 concentrations. They could be used for case-control studies investigating the association between perinatal vitamin D status and later health outcomes.

Sensitive high-performance liquid chromatographic method using coulometric electrode array detection for measurement of phytoestrogens in dried blood spots

As the epidemiological and physiological investigation of isoflavones and lignans expands, the need for sensitive methods for analyzing large numbers of samples intensifies. We have developed a method using high-performance liquid chromatography (HPLC) equipped with a coulometric electrode array detector for separation and sensitive detection of daidzein (Da), equol (Eq), genistein (Ge) and enterolactone (Enl) in dried blood spots (DBS). Detection limits ranged from 4.5 pg or 0.09 ng/mL (Eq) to 19 pg or 0.38 ng/mL (Ge) on column. Signal linearities ranged from detection limits to 200 ng/mL (Eq, Enl) and 600 ng/mL (Da, Ge) sample concentration. Correlations between DBS and serum concentrations were 0.66 (Enl), 0.88 (Eq), 0.98 (Ge) and 0.99 (Da). Intra-assay coefficients of variation (CVs) were less than 8% and inter-assay CVs ranged from 2.4 to 20.2% for Da, Eq and Ge for three levels of controls. Enl intra-assay CV was 13.6% for the low pooled control. Analytic recovery ranged from 87% (inter-assay Ge) to 98% (inter-assay Enl). DBS concentrations of Da, Ge and Eq were stable for at least 8 weeks at 4 and 25 degrees C, and at 37 degrees C for at least 5 weeks, with Enl showing greater variability at all temperatures but relative stability for 7 weeks. Measurement of samples from 135 perimenopausal Japanese women consuming habitual diets in Kyoto and Fukushima prefectures showed the former to have the expected lower concentrations of Da and Eq (416 and 87 nM) as well as Enl (49 nM) compared to the latter locale (566, 145 and 72 nM, respectively). This method could be useful in large epidemiological research or detailed physiological studies.