HPLC–MS method for the quantification of nine anti-HIV drugs from dry plasma spot on glass filter and their long term stability in different conditions

Biological Fluid Microsampling for Therapeutic Drug Monitoring: A Narrative Review

Therapeutic drug monitoring (TDM) is a specialized area of laboratory medicine which involves the measurement of drug concentrations in biological fluids with the aim of optimizing efficacy and reducing side effects, possibly modifying the drug dose to keep the plasma concentration within the therapeutic range. Plasma and/or whole blood, usually obtained by venipuncture, are the "gold standard" matrices for TDM. Microsampling, commonly used for newborn screening, could also be a convenient alternative to traditional sampling techniques for pharmacokinetics (PK) studies and TDM, helping to overcome practical problems and offering less invasive options to patients. Although technical limitations have hampered the use of microsampling in these fields, innovative techniques such as 3-D dried blood spheroids, volumetric absorptive microsampling (VAMS), dried plasma spots (DPS), and various microfluidic devices (MDS) can now offer reliable alternatives to traditional samples. The application of microsampling in routine clinical pharmacology is also hampered by the need for instrumentation capable of quantifying analytes in small volumes with sufficient sensitivity. The combination of microsampling with high-sensitivity analytical techniques, such as liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), is particularly effective in ensuring high accuracy and sensitivity from very small sample volumes. This manuscript provides a critical review of the currently available microsampling devices for both whole blood and other biological fluids, such as plasma, urine, breast milk, and saliva. The purpose is to provide useful information in the scientific community to laboratory personnel, clinicians, and researchers interested in implementing the use of microsampling in their routine clinical practice.

Extractive determination study of Etravirine by using Tpooo as an Analytical reagent in Pure and Pharmaceutical dosage forms

This study developed a sensitive and straightforward extractive spectroscopic method to estimate Etravirine (ETR) using TPooo as an analytical reagent in pure and pharmaceutical dosage forms. This method was achieved based on the extractable chloroform complex formed with Tropeoline ooo (TPooo) in an acidic media. Following Beer’s law, the extractable complex showed the absorbance maximum at 485nm at the concentration ranges between 12.5-75 µg/ml with the molar absorptivity 2.195 x 103 L/mole /cm and the Sandell’s sensitivity 0.1549 µg cm-2. The result of Etravirine estimation for the present method has been validated statistically by recovery studies, and the developed method was simple, sensitive, accurate, and precise. It was validated following International Conference on Harmonization (ICH) guidelines and also successfully applied for the estimation of Etravirine in tablet dosage forms.

A UHPLC-MS/MS Method for Therapeutic Drug Monitoring of Aciclovir and Ganciclovir in Plasma and Dried Plasma Spots

The role of therapeutic drug monitoring (TDM) of valaciclovir (VA)/aciclovir (A) and valganciclovir/ganciclovir (VG/G) in critically ill patients is still a matter of debate. More data on the dose–concentration relationship might therefore be useful, especially in pediatrics where clinical practice is not adequately supported by robust PK studies. We developed and validated a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) micro-method to simultaneously quantify A and G from plasma and dried plasma spots (DPS). The method was based on rapid organic extraction from DPS and separation on a reversed-phase C-18 UHPLC column after addition of deuterated internal standards. Accurate analyte quantification using SRM detection was then obtained using a Thermo Fisher Quantiva triple-quadrupole MS coupled to an Ultimate 3000 UHPLC. It was validated following international (EMA) guidelines for bioanalytical method validation and was tested on samples from pediatric patients treated with A, VG, or G for cytomegalovirus infection following solid organ or hematopoietic stem cell transplantation. Concentrations obtained from plasma and DPS were compared using Passing–Bablok and Bland–Altman statistical tests. The assay was linear over wide concentration ranges (0.01–20 mg/L) in both plasma and DPS for A and G, suitable for the expected therapeutic ranges for both Cmin and Cmax, accurate, and reproducible in the absence of matrix effects. The results obtained from plasma and DPS were comparable. Using an LC-MS/MS method allowed us to obtain a very specific, sensitive, and rapid quantification of these antiviral drugs starting from very low volumes (50 μL) of plasma samples and DPS. The stability of analytes for at least 30 days allows for cost-effective shipment and storage at room temperature. Our method is suitable for TDM and could be helpful for improving knowledge on PK/PD targets of antivirals in critically ill pediatric patients.

Determination of fluoroquinolones in dried plasma spots by using microwave-assisted extraction coupled to ultra-high performance liquid chromatography-tandem mass spectrometry for therapeutic drug monitoring

Therapeutic drug monitoring is important for achieving desirable outcomes in tuberculosis treatment. In this study, microwave-assisted extraction was used to extract levofloxacin, ciprofloxacin, and moxifloxacin from dried plasma spots for subsequent detection and quantification with ultra-high performance liquid chromatography-tandem mass spectrometry. Dried plasma spotting was performed by dropping 15 μL of plasma on a protein saver card. Analyte extraction was performed with microwave-assisted extraction at 400 W for 40 s in 90 % methanol. Samples were analyzed with a core-shell C18 column (100 mm × 2.1 mm, 2.6 μm, 100 Å). Multiple reaction monitoring was used and the ion source was operated in positive electrospray ionization mode. The correlation coefficients of the calibration curves were > 0.999 for all three drugs over a range of 0.2-20 μg/mL. The intraday precision (n = 5) of the peak area ratios of the analyte to the internal standard was between 1.3 and 4.0 % relative standard deviation (RSD). The intraday accuracy ranged from 93.6-106.9%. The interday (n = 3) precision of the peak area ratios ranged from 1.9 to 8.8 % RSD, and the accuracy ranged from 94.9-107.1%. Regarding clinical application, the quantification results for moxifloxacin from dried plasma spots (DPSs) were strongly similar to the results from the plasma samples, which showed that Pearson's rho > 0.949. The validation and application results showed that the developed method can be used as an efficient analytical technique for therapeutic drug monitoring of fluoroquinolones for patients with tuberculosis.

Quantitative microsampling for bioanalytical applications related to the SARS-CoV-2 pandemic: Usefulness, benefits and pitfalls

The multiple pathological effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and its total novelty, mean that currently a lot of diagnostic and therapeutic tools, established and tentative alike, are needed to treat patients in a timely, effective way. In order to make these tools more reliable, faster and more feasible, biological fluid microsampling techniques could provide many advantages. In this review, the most important microsampling techniques are considered (dried matrix spots, volumetric absorptive microsampling, microfluidics and capillary microsampling, solid phase microextraction) and their respective advantages and disadvantages laid out. Moreover, currently available microsampling applications of interest for SARS-CoV-2 therapy are described, in order to make them as much widely known as possible, hopefully providing useful information to researchers and clinicians alike.

A review of recent advances in microsampling techniques of biological fluids for therapeutic drug monitoring

Conventional sampling of biological fluids often involves a bulk quantity of samples that are tedious to collect, deliver and process. Miniaturized sampling approaches have emerged as promising tools for sample collection due to numerous advantages such as minute sample size, patient friendliness and ease of shipment. This article reviews the applications and advances of microsampling techniques in therapeutic drug monitoring (TDM), covering the period January 2015 - August 2020. As whole blood is the gold standard sampling matrix for TDM, this article comprehensively highlights the most historical microsampling technique, the dried blood spot (DBS), and its development. Advanced developments of DBS, ranging from various automation DBS, paper spray mass spectrometry (PS-MS), 3D dried blood spheroids and volumetric absorptive paper disc (VAPD) and mini-disc (VAPDmini) are discussed. The volumetric absorptive microsampling (VAMS) approach, which overcomes the hematocrit effect associated with the DBS sample, has been employed in recent TDM. The sample collection and sample preparation details in DBS and VAMS are outlined and summarized. This review also delineates the involvement of other biological fluids (plasma, urine, breast milk and saliva) and their miniaturized dried matrix forms in TDM. Specific features and challenges of each microsampling technique are identified and comparison studies are reviewed.

Review of Chromatographic Methods Coupled with Modern Detection Techniques Applied in the Therapeutic Drugs Monitoring (TDM)

Therapeutic drug monitoring (TDM) is a tool used to integrate pharmacokinetic and pharmacodynamics knowledge to optimize and personalize various drug therapies. The optimization of drug dosing may improve treatment outcomes, reduce toxicity, and reduce the risk of developing drug resistance. To adequately implement TDM, accurate and precise analytical procedures are required. In clinical practice, blood is the most commonly used matrix for TDM; however, less invasive samples, such as dried blood spots or non-invasive saliva samples, are increasingly being used. The choice of sample preparation method, type of column packing, mobile phase composition, and detection method is important to ensure accurate drug measurement and to avoid interference from matrix effects and drug metabolites. Most of the reported procedures used liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) techniques due to its high selectivity and sensitivity. High-performance chromatography with ultraviolet detection (HPLC-UV) methods are also used when a simpler and more cost-effective methodology is desired for clinical monitoring. The application of high-performance chromatography with fluorescence detection (HPLC-FLD) with and without derivatization processes and high-performance chromatography with electrochemical detection (HPLC-ED) techniques for the analysis of various drugs in biological samples for TDM have been described less often. Before chromatographic analysis, samples were pretreated by various procedures-most often by protein precipitation, liquid-liquid extraction, and solid-phase extraction, rarely by microextraction by packed sorbent, dispersive liquid-liquid microextraction. The aim of this article is to review the recent literature (2010-2020) regarding the use of liquid chromatography with various detection techniques for TDM.

Darunavir: A comprehensive profile

Darunavir: (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl [(2S,3R)-4-{[(4-aminophenyl)sulfonyl] (isobutyl)amino}-3-hydroxy-1-phenyl-2-butanyl]carbamate is a synthetic non-peptide protease inhibitor. On June 2006, it was first approved by the Food and Drug administration (FDA) for treatment of resistant type-1 of the human immunodeficiency virus (HIV). In July 2016, the FDA expanded the approval for use of darunavir in pregnant women with HIV infection. Darunavir prevents the replication of HIV virus by inhibiting the catalytic activity of the HIV-1 protease enzyme, and selectively inhibits the cleavage of HIV encoded Gag-Pol polyproteins in virus-infected cells, which prevents the formation of mature infectious virus particles. Darunavir is unique among currently available protease inhibitors because it maintains antiretroviral activity against a variety of multidrug-resistant HIV strains. This article discusses, by a critical extensive review of the literature, the description of darunavir in terms of its names, formulae, elemental composition, appearance, and use in the treatment of HIV-infected patients. The article also discusses the methods for preparation of darunavir, its physical-chemical properties, analytical methods for its determination, pharmacological properties, and dosing information.

Dried Blood Spot Tests for the Diagnosis and Therapeutic Monitoring of HIV and Viral Hepatitis B and C

Blood collected and dried on a paper card – dried blood spot (DBS) – knows a growing interest as a sampling method that can be performed outside care facilities by capillary puncture, and transported in a simple and safe manner by mail. The benefits of this method for blood collection and transport has recently led the World Health Organization to recommend DBS for HIV and hepatitis B and C diagnosis. The clinical utility of DBS sampling to improve diagnostics and care of HIV and hepatitis B and C infection in hard to reach populations, key populations and people living in low-income settings was highlighted. Literature about usefulness of DBS specimens in the therapeutic cascade of care – screening, confirmation, quantification of nucleic acids, and resistance genotyping -, was reviewed. DBS samples are suitable for testing antibodies, antigens, or nucleic acids using most laboratory methods. Good sensibility and specificity have been reported for infant HIV diagnosis and diagnosis of hepatitis B and C. The performance of HIV RNA testing on DBS to identified virological failure on antiretroviral therapy is also high but not optimal because of the dilution of dried blood in the elution buffer, reducing the analytical sensitivity, and because of the contamination by intracellular HIV DNA. Standardized protocols are needed for inter-laboratory comparisons, and manufacturers should pursue regulatory approval for in vitro diagnostics using DBS specimens. Despite these limitations, DBS sampling is a clinically relevant tool to improve access to infectious disease diagnosis worldwide.

Simple and Rapid Method by Ultra High-Performance Liquid Chromatography (UHPLC) with Ultraviolet Detection for Determination of Efavirenz in Plasma: Application in a Preclinical Pharmacokinetic Study

A simple and rapid ultra-high-performance liquid chromatography (UHPLC) method for determination of efavirenz (EFV) in plasma was developed and applied in a preclinical pharmacokinetic study. The method involves only addition of acetonitrile to precipitation of plasma proteins followed by solvent evaporation. The mobile phase consisted of methanol, acetonitrile and 0.1 M formic acid (20:50:30) at a flow rate of 0.3 mL/min with run time of 5 min. A CSH C18 column and a UHPLC-UV system operating at 245 nm were used. There was a linear response in the range of 0.078 to 10 μg/mL, and the equation was obtained by weighting (1/x2) with r2 = 0.9965. The pharmacokinetic disposition of EFV was investigated in rabbits (two groups, n = 7) following a single intravenous administration (IV group) at a dose of 2.7 mg/kg and a single oral administration (oral group) of EFV co-administered with lamivudine (3TC) and tenofovir (TNF) at a dose of 50, 25 and 25 mg, respectively. The study demonstrated the applicability of the method for determination of EFV in plasma without interference from other co-administered drugs, and the pharmacokinetic parameters were calculated. The method showed advantages over other methods in the literature, such as simplicity of sample processing and fast results.

Using dried blood spots to facilitate therapeutic drug monitoring of antiretroviral drugs in resource-poor regions

Objectives

We evaluated whether dried blood spots (DBS) are suitable to monitor combined ART when samples are collected in rural Tanzania and transported over a long distance to a specialized bioanalytical laboratory.

Methods

Plasma and DBS samples were collected in Tanzania from study patients treated with nevirapine, efavirenz or lopinavir. In addition, plasma, whole blood and DBS samples were obtained from a cohort of HIV patients at the site of the bioanalytical laboratory in Switzerland. DBS samples were analysed using a fully automated LC-MS/MS method.

Results

Comparison of DBS versus plasma concentrations of samples obtained from the bridging study in Switzerland indicated an acceptable bias only for nevirapine (18.4%), whereas for efavirenz and lopinavir a pronounced difference of -47.4% and -48.1% was found, respectively. Adjusting the DBS concentrations by the haematocrit and the fraction of drug bound to plasma proteins removed this bias [efavirenz +9.4% (-6.9% to +25.7%), lopinavir +2.2% (-20.0% to +24.2%)]. Storage and transportation of samples from Tanzania to Switzerland did not affect the good agreement between plasma and DBS for nevirapine [-2.9% (-34.7% to +29.0%)] and efavirenz [-9.6% (-42.9% to +23.8%)]. For lopinavir, however, adjusted DBS concentrations remained considerably below [-32.8% (-70.4% to +4.8%)] corresponding plasma concentrations due to decay of lopinavir in DBS obtained under field conditions.

Conclusions

Our field study shows that the DBS technique is a suitable tool for therapeutic drug monitoring in resource-poor regions; however, sample stability remains an issue for certain analytes and therefore needs special consideration.

Chemical profiling of the street cocktail drug 'nyaope' in South Africa using GC-MS II: Stability studies of the cannabinoid, opiate and antiretroviral components during sample storage

Nyaope is a mixture of low grade heroin, cannabis products, antiretroviral drugs and other materials added as bulking agents. It is a highly physically additive mixture which is smoked by users. As part of the development of a method for the analysis and profiling of nyaope this study evaluates the stability of the cannabinoid, opiate and antiretroviral components of nyaope during storage following seizure. Conditions used were those typically used for storage of drug seizures: in a desiccator in a refrigerator, in a desiccator in the dark at room temperature, in a desiccator in daylight at room temperature and ambient room temperature in the dark in a cabinet used for storage of drug seizures. Street samples of cannabis (Δ⁹-tetrahydrocannabinol) and heroin were mixed with efavirenz and nevirapine tablets to mimic a nyaope sample. The samples were homogenized and transferred into glass bottles and extracted with tertiary butyl alcohol (tBuOH) and analysed by gas chromatography - mass spectrometry (GC-MS) after the powdered drugs had been stored for intervals of 0 and 24 h under each storage condition. The data obtained indicates that the target drug components in nyaope samples decompose and that for comparison purposes the drug extracts should be prepared in tBuOH immediately after seizure because of the decomposition of the drug components during storage prior to extraction and analysis. The implications of this work are that law enforcement agencies dealing with nyaope and wanting to compare drug samples may need to change their practice around how the drug is handled after seizure but prior to analysis.

DBS-LC-MS/MS assay for caffeine: validation and neonatal application

AIM

DBS might be an appropriate microsampling technique for therapeutic drug monitoring of caffeine in infants. Nevertheless, its application presents several issues that still limit its use. This paper describes a validated DBS-LC-MS/MS method for caffeine.

RESULTS

The results of the method validation showed an hematocrit dependence. In the analysis of 96 paired plasma and DBS clinical samples, caffeine levels measured in DBS were statistically significantly lower than in plasma but the observed differences were independent from hematocrit.

CONCLUSION

These results clearly showed the need for extensive validation with real-life samples for DBS-based methods. DBS-LC-MS/MS can be considered to be a good alternative to traditional methods for therapeutic drug monitoring or PK studies in preterm infants.

Innovations in health and demographic surveillance systems to establish the causal impacts of HIV policies

PURPOSE OF REVIEW

Health and demographic surveillance systems (HDSS), in conjunction with HIV treatment cohorts, have made important contributions to our understanding of the impact of HIV treatment and treatment-related interventions in sub-Saharan Africa. The purpose of this review is to describe and discuss innovations in data collection and data linkage that will create new opportunities to establish the impacts of HIV treatment, as well as policies affecting the treatment cascade, on population health and economic and social outcomes.

RECENT FINDINGS

Novel approaches to routine collection of biomarkers, behavioural data, spatial data, social network information, migration events and mobile phone records can significantly strengthen the potential of HDSS to generate exposure and outcome data for causal analysis of HIV treatment impact and policies affecting the HIV treatment cascade. Additionally, by linking HDSS data to health service administration, education and welfare service records, researchers can substantially broaden opportunities to establish how HIV treatment affects health and economic outcomes when delivered through public sector health systems and at scale.

SUMMARY

As the HIV treatment scaleup in sub-Saharan Africa enters its second decade, it is becoming increasingly important to understand the long-term causal impacts of large-scale HIV treatment and related policies on broader population health outcomes, such as noncommunicable diseases, as well as on economic and social outcomes, such as family welfare and children's educational attainment. By collecting novel data and linking existing data to public sector records, HDSS can create near-unique opportunities to contribute to this research agenda.

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

Dried plasma/blood spots for monitoring antiretroviral treatment efficacy and pharmacokinetics: a cross-sectional study in rural Burundi

AIMS

In limited resource settings monitoring antiretroviral (ARV) treatment efficacy is restrained by the lack of access to technological equipment. The aim of the study was to assess the use of dried plasma (DPS) and blood spots (DBS) to facilitate ARV monitoring in remote settings where clinical monitoring is the primary strategy.

METHODS

A cross-sectional study in HIV-positive ARV-treated patients in Kiremba, Burundi was performed. DBS were used for HIV-1 viral load (limit of the assay 250 copies ml(-1)) and genotypic drug resistance tests and dried plasma spots were used for concentration measurements.

RESULTS

Three hundred and seven patients [201 female (88.6%), 14 children (4.5%)] were enrolled. HIV-1 viral load was <250, 250-1000 and >1000 copies ml(-1) in 250 (81.7%), 33 (10.8%) and 23 patients (7.5%). Eleven samples out of 23 were successfully amplified revealing nucleoside reverse transcriptase inhibitor (NRTI) and non-nucleoside reverse transcriptase inhibitor (NNRTI)-resistance associated mutations [in seven (58.3%) and six patients (50%)]. Nevirapine trough concentrations were <3000 ng ml(-1) in 28/189 patients (14.8%) and efavirenz 12 h concentrations were <1000 ng ml(-1) in 2/16 patients (12.5%). Children and patients with nevirapine exposure <3000 ng ml(-1) presented a higher risk of viral replication.

CONCLUSIONS

Viral loads <250 copies ml(-1) were observed in 81.7% of patients (83.6% adults and 42.9% children). Children and patients with low nevirapine concentrations had higher risk of viral replication. Dried blood and plasma spots may be useful for monitoring HIV-positive patients including viral load and drug level measurement as part of treatment management in remote areas.

A validated method for the quantification of fosfomycin on dried plasma spots by HPLC-MS/MS: application to a pilot pharmacokinetic study in humans

Quantification of fosfomycin in the plasma samples of patients is the basis of clinical pharmacokinetic studies from which evidence based dosing regimens can be devised to maximise antibiotic effectiveness against a pathogen. We have developed and validated a LC-MS/MS method to quantify fosfomycin using dried plasma spot sampling. Following HILIC chromatography, fosfomycin and ethylphosphonic acid, used as internal standard, were measured using negative-ion multiple reaction monitoring. The method was linear over the calibration range of 5-2000mg/L of fosfomycin. Intra-day assay results for dried plasma spot quality control samples at 15.6, 79.9 and 1581mg/L of fosfomycin had precision of ±4.2, 8.2, and 2.0%, respectively, and accuracy of +3.9, -0.1, and -1.2%, respectively. Recovery of fosfomycin from dried plasma spots was calculated as 83.6% and the dried plasma spot samples were found to be stable stored at room temperature for three months and when stored for four hours at 50°C. A Bland-Altman plot comparing DPS to plasma sampling found a negative bias of 16.6%, with all but one sample within the mean limits of agreement (-2.6 to 30.6%). Dried plasma spot sampling provides a useful tool for pharmacokinetic research of fosfomycin.

Development and validation of an ultra performance liquid chromatography tandem mass method for sildenafil and N-desmethyl sildenafil plasma determination and quantification

Sildenafil is a selective inhibitor of cGMP-specific type 5 phosphodiesterase (PDE5) used for the treatment of masculine erectile dysfunction and Pulmonary Arterial Hypertension (PAH). Sildenafil causes vasodilatation; relax of the smooth muscle and reduction of pulmonary arterial pressure. In the liver cytocrome P450 metabolizes sildenafil into its active metabolite, N-desmethyl sildenafil. The determination of plasma levels of sildenafil and N-desmethyl sildenafil could be useful for therapy optimization and pharmacokinetic studies. We have developed and validated a new method for the quantification of sildenafil and its metabolite in human plasma by rapid protein precipitation extraction, using an UPLC system, coupled with a tandem mass spectrometric detector (UPLC-MS/MS). The calibration range was fitted at least square model (r(2)≥0.999), with an accuracy and an intra- and inter-day RSD% (Relative Standard Deviation), both for sildenafil and N-desmethyl sildenafil, lower than 15%, as required by the FDA guidelines; LLOQ, LLOD, ULOQ were 3.9ng/mL, 1.95ng/mL and 1000ng/mL, respectively, for both analytes. Matrix effect, expressed as mean percent deviation of peak areas, was in the range between 2.6% and 5.8%, lower than 15% as required by guidelines. The mean recovery was 83.2 % for sildenafil and 84.5% for N-desmethyl sildenafil. This method has successfully been applied to a clinical pharmacokinetic study of sildenafil and N-desmethyl sildenafil in patients with PAH undergoing cardiac surgery.

A critical review of properties of darunavir and analytical methods for its determination

Darunavir is a synthetic non-peptidic protease inhibitor that has been shown to be extremely potent against wild-type HIV, and it is an important component of highly active antiretroviral treatment (HAART), which is considered as one of the most significant advances in the field of HIV therapy. However, there are some concerns about darunavir quality control. Darunavir shows pseudo-polymorphism: in different ambient conditions one pseudo-polymorphic form can change to another. This behavior of darunavir is problematic because the dosage form is exposed to different ambient conditions around the world, since HIV/AIDS is prevalent globally. Issues around differences in the solubility and effects that different forms of darunavir can cause are of concern, and a more stable form is preferable. Important investigations of darunavir such as dissolution behavior, polymorphism, stability and degradation studies, and the impact of that on the quality of the product are being conducted by our working group. A cure for HIV/AIDS remains a long-term commitment, and there is much yet to achieve. This article discusses, by a critical review of the literature, the impact of the use of darunavir in the treatment of HIV-infected patients, its physical-chemical properties, the analytical methods to determine it, and challenges that remain in order to ensure the quality and stability of darunavir.

Validation and clinical application of a method to quantify nevirapine in dried blood spots and dried breast-milk spots

OBJECTIVES

The validation and clinical application of an LC-MS/MS method for the quantification of nevirapine in dried blood spots (DBS) and dried breast-milk spots (DBMS) are presented.

METHODS

DBS and DBMS were prepared from 50 and 30 μL of nevirapine-spiked whole blood and human breast milk, respectively. Chromatographic separation was achieved on a reverse-phase C18 column with 0.1% formic acid in water/acetonitrile using a solvent gradient programme at a flow rate of 400 μL/min, and detection was by a TSQ Quantum Access triple quadrupole mass spectrometer. The clinical application was evaluated in HIV-positive nursing mothers and their breastfed infants.

RESULTS

The assay was validated over the concentration range 50-10,000 ng/mL. Accuracy ranged from 93.3% to 113.4% and precision ranged from 1.9% to 12.0%. The mean (percentage coefficient of variation) recovery of nevirapine from DBS and DBMS was ≥ 70.7% (≤ 8.2) and the matrix effect was ≤ 1.04 (≤ 6.1). Nevirapine was stable in DBS and DBMS for ≥ 15 months at room temperature and -80°C. Mean (SD) AUC0-12, Cmax and Cmin in maternal plasma versus breast milk were 57,808 ng · h/mL (24,315) versus 55,817 ng · h/mL (22,368), 6140 ng/mL (2605) versus 5231 ng/mL (2215) and 4334 ng/mL (1880) versus 4342 ng/mL (2245), respectively. The milk-to-plasma concentration ratio over the dosing interval was 0.94 (0.15). Infant plasma concentrations 2 and 8 h after maternal dosing were 580.6 ng/mL (464.7-1607) and 584.1 ng/mL (381.5-1570), respectively.

CONCLUSIONS

These methods further extend opportunities for conducting clinical pharmacokinetic studies in nursing mother-infant pairs, especially in resource-limited settings.

Direct injection HILIC-MS/MS analysis of darunavir in rat plasma applying supported liquid extraction

A novel bioanalytical method was developed and validated for the quantitative determination of darunavir (DRV) in rat plasma by employing hydrophilic interaction chromatography and tandem mass spectrometry (HILIC-MS/MS) with supported liquid extraction (SLE). Irbesartan (IRB) was used as an internal standard (IS). The analyte in rat plasma (200 µL) was isolated through SLE using ethyl acetate as the eluting solvent. The chromatographic separation was achieved on Luna-HILIC (250 mm×4.6 mm, 5 μm) column with a mobile phase of 0.1% of formic acid in water:acetonitrile (5: 95, v/v), at a constant flow rate of 1.0 mL/min. The MS/MS ion transitions for DRV (548.1→392.0) and IS (429.2→207.1) were monitored on an ion trap mass spectrometer, operating in the multiple reaction monitoring (MRM) mode. The lower limit of quantitation (LLOQ) was 0.2 ng/mL and quantitation range was 0.2-5000 ng/mL. The method was validated for its selectivity, sensitivity, carryover, linearity, precision, accuracy, recovery, matrix effect and stability. The method was successfully applied to pharmacokinetic study in rats.

Therapeutic drug monitoring by dried blood spot: progress to date and future directions

This article discusses dried blood spot (DBS) sampling in therapeutic drug monitoring (TDM). The most important advantages of DBS sampling in TDM are the minimally invasive procedure of a finger prick (home sampling), the small volume (children), and the stability of the analyte. Many assays in DBS have been reported in the literature over the previous 5 years. These assays and their analytical techniques are reviewed here. Factors that may influence the accuracy and reproducibility of DBS methods are also discussed. Important issues are the correlation with plasma/serum concentrations and the influence of hematocrit on spot size and recovery. The different substrate materials are considered. DBS sampling can be a valid alternative to conventional venous sampling. However, patient correlation studies are indispensable to prove this. Promising developments are dried plasma spots using membrane and hematocrit correction using the potassium concentration.

Current and future use of "dried blood spot" analyses in clinical chemistry

The analysis of blood spotted and dried on a matrix (i.e., "dried blood spot" or DBS) has been used since the 1960s in clinical chemistry; mostly for neonatal screening. Since then, many clinical analytes, including nucleic acids, small molecules and lipids, have been successfully measured using DBS. Although this pre-analytical approach represents an interesting alternative to classical venous blood sampling, its routine use is limited. Here, we review the application of DBS technology in clinical chemistry, and evaluate its future role supported by new analytical methods such as mass spectrometry.

Validation of simultaneous quantitative method of HIV protease inhibitors atazanavir, darunavir and ritonavir in human plasma by UPLC-MS/MS

OBJECTIVES

HIV protease inhibitors are used in the treatment of patients suffering from AIDS and they act at the final stage of viral replication by interfering with the HIV protease enzyme. The paper describes a selective, sensitive, and robust method for simultaneous determination of three protease inhibitors atazanavir, darunavir and ritonavir in human plasma by ultra performance liquid chromatography-tandem mass spectrometry.

MATERIALS AND METHODS

The sample pretreatment consisted of solid phase extraction of analytes and their deuterated analogs as internal standards from 50 μL human plasma. Chromatographic separation of analytes was performed on Waters Acquity UPLC C18 (50 × 2.1 mm, 1.7 μm) column under gradient conditions using 10 mM ammonium formate, pH 4.0, and acetonitrile as the mobile phase.

RESULTS

The method was established over a concentration range of 5.0-6000 ng/mL for atazanavir, 5.0-5000 ng/mL for darunavir and 1.0-500 ng/mL for ritonavir. Accuracy, precision, matrix effect, recovery, and stability of the analytes were evaluated as per US FDA guidelines.

CONCLUSIONS

The efficiency of sample preparation, short analysis time, and high selectivity permit simultaneous estimation of these inhibitors. The validated method can be useful in determining plasma concentration of these protease inhibitors for therapeutic drug monitoring and in high throughput clinical studies.

Hemato-critical issues in quantitative analysis of dried blood spots: challenges and solutions

Dried blood spot (DBS) sampling for quantitative determination of drugs in blood has entered the bioanalytical arena at a fast pace during the last decade, primarily owing to progress in analytical instrumentation. Despite the many advantages associated with this new sampling strategy, several issues remain, of which the hematocrit issue is undoubtedly the most widely discussed challenge, since strongly deviating hematocrit values may significantly impact DBS-based quantitation. In this review, an overview is given of the different aspects of the ‘hematocrit problem’ in quantitative DBS analysis. The different strategies that try to cope with this problem are discussed, along with their potential and limitations. Implementation of some of these strategies in practice may help to overcome this important hurdle in DBS assays, further allowing DBS to become an established part of routine quantitative bioanalysis.

A sensitive and selective liquid chromatography/tandem mass spectrometry method for quantitative analysis of efavirenz in human plasma

A selective and a highly sensitive method for the determination of the non-nucleoside reverse transcriptase inhibitor (NNRTI), efavirenz, in human plasma has been developed and fully validated based on high performance liquid chromatography tandem mass spectrometry (LC-MS/MS). Sample preparation involved protein precipitation followed by one to one dilution with water. The analyte, efavirenz was separated by high performance liquid chromatography and detected with tandem mass spectrometry in negative ionization mode with multiple reaction monitoring. Efavirenz and ¹³C₆-efavirenz (Internal Standard), respectively, were detected via the following MRM transitions: m/z 314.20243.90 and m/z 320.20249.90. A gradient program was used to elute the analytes using 0.1% formic acid in water and 0.1% formic acid in acetonitrile as mobile phase solvents, at a flow-rate of 0.3 mL/min. The total run time was 5 min and the retention times for the internal standard (¹³C₆-efavirenz) and efavirenz was approximately 2.6 min. The calibration curves showed linearity (coefficient of regression, r>0.99) over the concentration range of 1.0-2,500 ng/mL. The intraday precision based on the standard deviation of replicates of lower limit of quantification (LLOQ) was 9.24% and for quality control (QC) samples ranged from 2.41% to 6.42% and with accuracy from 112% and 100-111% for LLOQ and QC samples. The inter day precision was 12.3% and 3.03-9.18% for LLOQ and quality controls samples, and the accuracy was 108% and 95.2-108% for LLOQ and QC samples. Stability studies showed that efavirenz was stable during the expected conditions for sample preparation and storage. The lower limit of quantification for efavirenz was 1 ng/mL. The analytical method showed excellent sensitivity, precision, and accuracy. This method is robust and is being successfully applied for therapeutic drug monitoring and pharmacokinetic studies in HIV-infected patients.

Stability Study of Darunavir Ethanolate Tablets Applying a New Stability-Indicating HPLC Method

Chemical and physical degradation of drugs may result in altered therapeutic efficacy and even toxic effects. Therefore, the aim of this work was to study the stability of darunavir and to develop and validate a liquid chromatography (LC) method to determine darunavir in raw material and tablets in the presence of degradation products. The novel method showed to be linear from 6.0 to 21.0 μg/mL, with high precision (CV < 2%) and accuracy (recuperation of 99.64%). It is simple and reliable, free of placebo interferences. The robustness of the method was evaluated by a factorial design using seven different parameters. Forced degradation study was done under alkaline, acidic, and oxidative stress at ambient temperature and by heating. The LC method was able to quantify and separate darunavir and its degradation products. Darunavir showed to be unstable under alkaline, acid, and oxidative conditions. The novelty of this study is understanding the factors that affect darunavir ethanolate stability in tablets, which is the first step to unravel the path to know the degradation products. The novel stability-indicating method can be used to monitor the drug and the main degradation products in low concentrations in which there is linearity.

Influence of CYP2B6 and ABCB1 SNPs on nevirapine plasma concentrations in Burundese HIV-positive patients using dried sample spot devices

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Nevirapine pharmacokinetics are affected by several factors including CYP2B6 single nucleotide polymorphisms (SNPs). These genetic profiles are more common in African patients and they affect the drug clearance being associated with higher trough concentrations. Pharmacokinetic/pharmacogenetic (PK/PG) studies are difficult to perform in remote areas where refrigeration is not available, although dried plasma and dried blood methods have been validated.

WHAT THIS STUDY ADDS

• Dried plasma spots are useful tools for studying nevirapine PK with a good association to plasma concentrations and they can be used in rural areas since a cold chain is not necessary. Dried blood spots can be used to store and analyze patients' DNA for PG polymorphisms. Nevirapine trough concentrations in Burundese patients, not studied so far, are above the target concentration (3000 ng ml(-1) ) in 84% of patients. CYP2B6 (both at position 516 and 983) but not ABCB1 (3435 and 1236) SNPs as well as age correlate with higher nevirapine exposure.

AIMS

The pharmacokinetics (PK) and pharmacogenetics (PG) of nevirapine have been studied in rich and limited-resource countries. CYP2B6 single nucleotide polymorphisms (SNPs) have been associated with decreased drug clearance. We evaluated the PG determinants of nevirapine trough concentrations in a rural cohort in Burundi using easy to store and transport dried sample spot devices.

METHODS

A cross-sectional analysis in HIV-positive nevirapine-treated patients in Kiremba, north of Burundi, was performed in 2009. After blood withdrawal whole blood was stored on dried blood spots and plasma (after centrifugation) was placed on dried plasma spot devices and stored at room temperature. Nevirapine plasma and dried sample spot concentrations were compared to test the clinical usefulness of this method. SNPs in CYP2B6 and ABCB1 (using a real time PCR technique) were analyzed and associated with nevirapine plasma trough concentrations.

RESULTS

Nevirapine concentrations measured on dried plasma spot devices were highly related to plasma concentrations in 60 patients, although a negative bias was observed (-18%). Nevirapine trough concentrations were above the target concentration (3000 ng ml(-1) ) in 84% of patients and they were associated with CYP2B6 SNPs (both at position 516 and 983). No effect of ABCB1 SNPs was noted.

CONCLUSIONS

Dried plasma spot devices are accurate tools for measuring nevirapine concentrations in rural settings where refrigeration is not available, despite a moderate underestimation bias. They allowed the evaluation of nevirapine concentrations in a cohort of HIV-infected people in rural Burundi, confirming very good exposure and correlation with PG polymorphisms in the CYP2B6 encoding gene.