Single-Drop Blood Detection of Common G6PD Mutations in Thailand Based on Allele-Specific Recombinase Polymerase Amplification with CRISPR-Cas12a

Glucose 6-phosphate dehydrogenase (G6PD) deficiency is the most common inherited enzymopathy. Identification of the G6PD deficiency through screening is crucial to preventing adverse effects associated with hemolytic anemia following antimalarial drug exposure. Therefore, a rapid and precise field-based G6PD deficiency diagnosis is required, particularly in rural regions where malaria is prevalent. The phenotypic diagnosis of the G6PD intermediate has also been a challenging issue due to the overlapping of G6PD activity levels between deficient and normal individuals, leading to a misinterpretation. The availability of an accurate point-of-care testing (POCT) for G6PD genotype diagnosis will therefore increase the opportunity for screening heterozygous cases in a low-resource setting. In this study, an allele-specific recombinase polymerase amplification (AS RPA) with clustered regularly interspaced short palindromic repeats-Cas12a (CRISPR-Cas12a) was developed as a POCT for accurate diagnosis of common G6PD mutations in Thailand. The AS primers for the wild type and mutant alleles of G6PD MahidolG487A and G6PD ViangchanG871A were designed and used in RPA reactions. Following application of CRISPR-Cas12a systems containing specific protospacer adjacent motif, the targeted RPA amplicons were visualized with the naked eye. Results demonstrated that the G6PD MahidolG487A and G6PD ViangchanG871A assays reached 93.62 and 98.15% sensitivity, respectively. The specificity was 88.71% in MahidolG487A and 99.02% in G6PD ViangchanG871A. The diagnosis accuracy of the G6PD MahidolG487A and G6PD ViangchanG871A assays was 91.67 and 98.72%, respectively. From DNA extraction to detection, the assay required approximately 52 min. In conclusion, this study demonstrated the high performance of an AS RPA with the CRISPR-Cas12a platform for G6PD MahidolG487A and G6PD ViangchanG871A detection assays and the potential use of G6PD genotyping as POCT.

Comparison of florfenicol depletion in dairy goat milk using ultra-performance liquid chromatography with tandem mass spectrometry and a commercial on-farm test

Florfenicol is a broad-spectrum antibiotic commonly prescribed in an extra-label manner for treating meat and dairy goats. Scientific data in support of a milk withdrawal interval recommendation is limited to plasma pharmacokinetic data and minimal milk residue data that is limited to cattle. Therefore, a rapid residue detection test (RRDT) could be a useful resource to determine if milk samples are free of drug residues and acceptable for sale. This study compared a commercially available RRDT (Charm^® FLT strips) to detect florfenicol residues in fresh milk samples from healthy adult dairy breed goats treated with florfenicol (40 mg/kg subcutaneously twice 4 days apart) with quantitative analysis of florfenicol concentrations using ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS). In addition, storage claims for testing bovine milk using the RRDT were assessed using stored goat milk samples. Milk samples were collected every 12 h for a minimum of 26 days. Commercial RRDT strips remained positive in individual goats ranging from 528 to 792 h (22–33 days) after the second dose, whereas, UPLC-MS/MS indicated the last detectable florfenicol concentration in milk samples ranged from 504 to 720 h (21–30 days) after the second dose. Results from stored milk samples from treated goats indicate that samples can be stored for up to 5 days in the refrigerator and 60 days in the freezer after milking prior to being tested with a low risk of false-negative test results due to drug degradation. Elevated somatic cell counts and bacterial colony were noted in some of the milk samples in this study, but further study is required to understand the impact of these quality factors on RRDT results.

Reversed-phase high-performance liquid chromatography: A fast and efficient analytical method to quantify docetaxel-loaded pegylated liposomes in release study

Docetaxel is an anticancer that belongs to the family of taxanes and acts in the inhibition of cell proliferation through the polymerization of microtubules. The aim of this study was the development and validation of a fast method by reversed-phase high-performance liquid chromatography for quantitative analysis of docetaxel encapsulated in pegylated liposomes. The analytical method was validated for the following recognized specifications: system suitability, precision (repeatability and intermediate precision), linearity, accuracy, selectivity, detection and quantification limits, and robustness. The reversed phase-high-performance liquid chromatography analyses were performed at a temperature of 45°C (isocratic mode). The mobile phase was composed of acetonitrile and water (65:35, v/v) and the flow rate was fixed at 0.8 mL/min. The running time and wavelength were 8 min and 230 nm, respectively. The method was found to be linear, precise, selective, precise, robust, accurate, in the range of 1-75 μg/mL (R² = 0.9999) and the values of detection and quantification limits were 2.35 and 7.84 μg/mL, respectively. The release rates of docetaxel in pegylated liposomes were lower compared to docetaxel in solution. The reversed phase high-performance liquid chromatography method developed proved to be adequate and can be effectively used to determine the in vitro release profile of docetaxel transported by pegylated liposomes.

Update to the European Bioanalysis Forum recommendation on biomarkers assays; bringing context of use into practice

In 2012, the European Bioanalysis Forum published a recommendation on biomarker method development and the bioanalysis of biomarkers in support of drug development. Since then, there has been significant discussion on how to bring the topic of context of use of biomarker assays to the forefront so that the purpose of the assay, the use of the data and the decisions being made with the data are well defined and clearly understood, not just by the bioanalytical scientist, but across all stakeholders. Therefore, it is imperative that discussions between the bioanalytical laboratory and the end users of the data happen early (and regularly) in the drug development process to enable the right assays to be developed and appropriately validated to generate the correct data and allow suitable decisions to be made. This updated refinement to the previous European Bioanalysis Forum recommendation will highlight the items to consider when discussing context of use for biomarker assay development and validation, thus enabling the correct conversations to occur and the move away from the misapplication of PK assay validation criteria to biomarker assays.

Tools for quantitative analysis: The Al Yergey perspective

The development of a reliable quantitative method for a specific application requires consideration of several important principles. Although mass spectrometry has become the "gold standard" for sensitive and precise multicomponent quantification, it does not necessarily follow that all quantitative data generated by mass spectrometry are either precise or accurate. Depending on the nature of the sample and the goal of the assay, the endeavor can be challenging. With attention to some critical concerns, valid results can be obtained; without attention to these concerns, results can be misleading and, in some instances, invalid. For almost 10 years, beginning in 1996, the authors of this article, together with their friend and colleague Al Yergey, taught an American Society for Mass Spectrometry (ASMS) Short Course on the principles of quantitative mass spectrometry. In this Special Feature, we revisit and update some of these principles. We pay special attention to the contributions of Al Yergey to the course that not only enriched our own understanding of quantitative analysis but also had a measurable impact on the entire field of mass spectrometry.

A pilot study to investigate the measurement of immunoglobulin A in Welsh Cob and Welsh Pony foals' faeces and their dam's milk

Aims: To determine if an ELISA for measurement of IgA in equine serum could be used to measure concentrations of IgA in foal faeces and to determine correlations with concentrations in the milk of the dam.Methods: Faeces from 20 Welsh Cob and Welsh Pony foals and milk from their dams were collected within 12 hours (Day 0) and at 6 days after parturition (Day 6). On Day 6, faeces could not be collected from 2/20 foals, and milk samples could not be collected from 3/20 mares. An equine IgA ELISA validated for serum and plasma was used to measure concentrations of IgA in all samples in triplicate. The precision of the assay for each sample type was determined using modified CV.Results: IgA was not detectable in 7/20 Day 0 faecal samples and in 2/18 Day 6 faecal samples. For samples with detectable IgA, the mean modified CV was 10.5 (95% CI = 6.0-15.0)% for Day 0 faecal samples, and was 6.8 (95% CI = 4.3-9.4)% for Day 6 faecal samples. Median concentrations of IgA in faeces on Day 0 were lower than concentrations on Day 6 (0.7 mg/g vs. 37 mg/g dry matter; p = 0.003). Concentrations of IgA in milk and faeces on Day 6 were statistically correlated (r = 0.59; p = 0.006).Conclusions and clinical relevance: The IgA ELISA showed acceptable precision when used to estimate concentrations of IgA in foal faeces during the first week of life, but IgA could not be detected in 37% of meconium samples collected on Day 0. This assay may be useful for investigation of the role of maternal milk IgA in the gastrointestinal tract of neonatal foals, but further assessment of both accuracy and precision of the ELISA is required.

Incurred Sample Reanalysis: Time to Change the Sample Size Calculation?

Reliable results of pharmacokinetic and toxicokinetic studies are vital for correct decision making during drug discovery and development. Thus, ensuring high quality of bioanalytical methods is of critical importance. Incurred sample reanalysis (ISR)-one of the tools used to validate a method-is included in the bioanalytical regulatory recommendations. The methodology of this test is well established, but the estimation of the sample size is still commented on and contested. We have applied the hypergeometric distribution to evaluate ISR test passing rates in different clinical study sizes. We have tested both fixed rates of the clinical samples-as currently recommended by FDA and EMA-and a fixed number of ISRs. Our study revealed that the passing rate using the current sample size calculation is related to the clinical study size. However, the passing rate is much less dependent on the clinical study size when a fixed number of ISRs is used. Thus, we suggest using a fixed number of ISRs, e.g., 30 samples, for all studies. We found the hypergeometric distribution to be an adequate model for the assessment of similarities in original and repeated data. This model may be further used to optimize the sample size needed for the ISR test as well as to bridge data from different methods. This paper provides a basis to re-consider current ISR recommendations and implement a more statistically rationalized and risk-controlled approach.

Bioanalytical method validation: new FDA guidance vs. EMA guideline. Better or worse?

Bioanalysis concerns the identification and quantification of analytes in various biological matrices. Validation of any analytical method helps to achieve reliable results that are necessary for proper decisions on drug dosing and patient safety. In the case of bioanalytical methods, validation additionally covers steps of pharmacokinetic and toxicological studies - such as sample collection, handling, shipment, storage, and preparation. We drew our attention to the difference of both the newest FDA Guidance and the EMA Guideline on bioanalytical method validation. We aimed to point out advantages of both documents from the laboratory perspective. The FDA and the EMA documents are similar, but not identical. The EMA describes the practical conduct of experiments more precisely, while the FDA presents reporting recommendations more comprehensively. There are also differences in recommended validation parameters. We hope that the International Council for Harmonisation will combine advantages of both documents to avoid confusing differences in terminology as well as the unnecessary effort of being compliant with two or more guidelines.

Implementing a tiered approach to bioanalytical method validation for large-molecule ligand-binding assay methods in pharmacokinetic assessments

Bioanalytical methods must enable the delivery of data that meet sound, scientifically justified, fit-for-purpose criteria. At early phases of biotherapeutic drug development, suitable criteria of a ligand-binding assay could be met for pharmacokinetic (PK) in-study sample testing without a full validation defined by regulatory guidelines. To ensure fit-for-purpose methods support PK testing through all phases of biotherapeutic development, three tiers of method validation - regulatory, scientific and research validations - are proposed. The three-tiered framework for method validation outlines the differences in the parameters that should be assessed, the acceptance criteria that may be applied, and the documentation necessary at each level. The criteria for selecting the appropriate application of each of these PK method validation workflows are discussed.

The application of NMR-based milk metabolite analysis in milk authenticity identification

BACKGROUND

Milk is an important food component in the human diet and is a target for fraud, including many unsafe practices. For example, the unscrupulous adulteration of soymilk into bovine and goat milk or of bovine milk into goat milk in order to gain profit without declaration is a health risk, as the adulterant source and sanitary history are unknown. A robust and fit-for-purpose technique is required to enforce market surveillance and hence protect consumer health. Nuclear magnetic resonance (NMR) is a powerful technique for characterization of food products based on measuring the profile of metabolites. In this study, 1D NMR in conjunction with multivariate chemometrics as well as 2D NMR was applied to differentiate milk types and to identify milk adulteration.

RESULTS

Ten metabolites were found which differed among milk types, hence providing characteristic markers for identifying the milk. These metabolites were used to establish mathematical models for milk type differentiation. The limit of quantification (LOQ) of adulteration was 2% (v/v) for soymilk in bovine milk, 2% (v/v) for soymilk in goat milk and 5% (v/v) for bovine milk in goat milk, with relative standard deviation (RSD) less than 10%, which can meet the needs of daily inspection.

CONCLUSION

The NMR method described here is effective for milk authenticity identification, and the study demonstrates that the NMR-based milk metabolite analysis approach provides a means of detecting adulteration at expected levels and can be used for dairy quality monitoring. © 2016 Society of Chemical Industry.

Scientific or regulated validation: a tiered approach? Meeting report from a joint EBF/DVDMDG workshop

Tiered approach is rapidly gaining interest in the regulated bioanalytical community. Alternative approaches to the workflows as proposed in the regulatory Guidance (US FDA, EMA) are being used in discovery and early drug development, but with a growing array of assay types and studies requiring bioanalytical support in early drug development, the bioanalytical community is discussing how to bring best value to support these studies. Recently, international industry groups like European Bioanalysis Forum and Global Bioanalysis Consortium have discussed and published on the opportunity and need to include tiered approach more systematically in the early drug development support. On the back of these discussions, the Delaware Valley Drug Metabolism Discussion Group together with the European Bioanalysis Forum organized a meeting in Langhorne (PA, USA) to discuss the hurdles and added value of tiered approach with stakeholders from the Bioanalysis, quality assurance and PK community. The discussions focused on proposing scientific validation for studies where there is currently a mixed use of regulatory and tiered approach workflows. The meeting was well attended and the presentations and panel discussions contributed to a better understanding of what the industry is proposing as future practice.

Workshop report: Crystal City V--quantitative bioanalytical method validation and implementation: the 2013 revised FDA guidance

In September 2013, the FDA released a draft revision of the Bioanalytical Method Validation (BMV) Guidance, which included a number of changes to the expectations for bioanalysis, most notably the inclusion of biomarker assays and data. To provide a forum for an open, inclusive discussion of the revised draft BMV Guidance, the AAPS and FDA once again collaborated to convene a two-and-a-half day workshop during early December 2013 in Baltimore, MD, USA. The resulting format embodied extensive open discussion and each thematic session included only brief, concise descriptions by Agency and industry representatives prior to opening the floor discussion. The Workshop was built around four thematic sessions (Common Topics, Chromatographic, Ligand-Binding Assays, and Biomarkers) and a final session with international regulators, concluding with a review of the outcomes and recommendations from the thematic sessions. This Workshop report summarizes the outcomes and includes topics of agreement, those where the FDA will consider the Industry's perspective, and those where the workshop provided a first open dialogue. This article will be available to the bioanalytical community at http://www.aaps.org/BMV13 .

Safety, tolerability and pharmacokinetic properties of the novel triazene TriN 2755 in tumour bearing dogs - a phase I study†

TriN 2755 is an alkylating antineoplastic agent for intravenous (IV) use, carrying the triazene group as the cytotoxic principal. Using a standard 3 + 3 design, a phase I study was performed in tumour bearing dogs to determine the maximum tolerated dose (MTD), the dose limiting toxicity (DLT), and pharmacokinetic (PK) profile of TriN 2755. Thirty dogs were included in the study. TriN 2755 was administered over 20 min on two consecutive weeks per month for a total of three cycles. The starting dose was 25 mg kg^-1 and the MTD was 74.6 mg kg^-1 . Three dogs experienced DLT, which was characterized by gastrointestinal adverse events. The PKs of TriN 2755 and its main metabolites in plasma and sputum are described in a two-compartment model. The response rate for 19 of 30 dogs was 47.3% (six partial remission, three stable disease) and the median progression-free interval (PFI) for the responders was 47 days (range: 21-450 days).

Tiered approaches to chromatographic bioanalytical method performance evaluation: recommendation for best practices and harmonization from the Global Bioanalysis Consortium harmonization team

The A2 harmonization team, a part of the Global Bioanalysis Consortium (GBC), focused on defining possible tiers of chromatographic-based bioanalytical method performance. The need for developing bioanalytical methods suitable for the intended use is not a new proposal and is already referenced in regulatory guidance language. However, the practical implementation of approaches that differ from the well-established full validation requirements has proven challenging. Advances in technologies, the need to progress drug development more efficiently, and emerging new drug compound classes support the use of categorized tiers of bioanalytical methods. This paper incorporated the input from an international team of experienced bioanalysts to surmise the advantages and the challenges of tiered approaches and to provide recommendations on paths forward.

Highly linear pH gradients for analyzing monoclonal antibody charge heterogeneity in the alkaline range: Validation of the method parameters

Cation exchange chromatography has been routinely used for the quantification of monoclonal antibody (mAb) charge heterogeneity. A previously developed method utilizing pH gradients for the elution instead of salt gradients was validated according to current guidelines proposed by the ICH. The linearity, stability, accuracy, precision and the lower limit of quantification have been determined, using pure charge variant standards. The method is valid for the quantification of mAb samples with a charge heterogeneity between 1% and 50%. Three different approaches to obtaining pure standard material for the validation of bio-analytical methods for the quantification of charge heterogeneity of IgG are presented. These methods are based on salt gradient elution, pH gradient elution and displacement in cation exchange chromatography.

Glucose and glycerol concentrations and their tracer enrichment measurements using liquid chromatography tandem mass spectrometry

The present study describes a new liquid chromatography tandem mass spectrometry method for high-throughput quantification of glucose and glycerol in human plasma using stable isotopically labeled internal standards and is suitable for simultaneous measurements of glucose and glycerol enrichments in connection to in vivo metabolic studies investigating glucose turnover and lipolytic rate. Moreover, in order to keep up with this new fast analysis, simple derivatization procedures have been developed. Prior to analysis, glucose and glycerol were derivatized using benzoyl chloride in order to form benzoylated derivatives via new simplified fast procedures. For glucose, two internal standards were evaluated, [U-(13) C(6)]glucose and [U-(13) C(6), D(7)]glucose, and for glycerol, [U-(13) C(3), D(8)]glycerol was used. The method was validated by means of calibration curves, quality control samples, and plasma samples spiked with [6,6-D(2)]glucose, [U-(13) C(6)]glucose, and [1,1,2,3,3-D(5)]glycerol in order to test accuracy, precision, and recovery of the method. Moreover, post preparative and freeze-thaw sample stability were tested. The correlation of calibration curves for the glucose concentration were r(2) = 0.9998 for [U-(13) C(6)]glucose and r(2) = 0.9996 for [U-(13) C(6), D(7)]glucose, and r(2) = 0.9995 for the glycerol concentration. Interday accuracy for glucose using [U-(13) C(6)]glucose and glycerol determined in spiked plasma were respectively 103.5% and 106.0%, and the coefficients of variation were 2.0% and 9.7%, respectively. After derivatization, plasma samples were stable for at least 14 days. In conclusion, we have developed and validated a novel, accurate, and sensitive high-throughput liquid chromatography tandem mass spectrometry method for simultaneous determination of glucose and glycerol concentrations and enrichment of infused tracers most commonly used in human metabolic kinetic studies.

Some unnecessary or inadequate common practices in regulated LC–MS bioanalysis

The global bioanalytical community increasingly craves scientifically sound practices and guidance where the rationale is given for each requirement. To this end, it is critical to first evaluate all the existing practices and requirements based on scientific findings and critical thinking. Here we are challenging several important common practices in regulated LC–MS bioanalysis, from the requirement of at least six different calibration concentrations, no extrapolation, use of blank and zero standard in each batch, selection of quality controls, to the way matrix effect and dilution integrity are being validated. Both the reasons why these common practices are unnecessary or inadequate and the potential solutions are presented.

Repeat analysis and incurred sample reanalysis: recommendation for best practices and harmonization from the global bioanalysis consortium harmonization team

The A7 harmonization team (A7 HT), a part of the Global Bioanalysis Consortium (GBC), focused on reviewing best practices for repeat analysis and incurred sample reanalysis (ISR) as applied during regulated bioanalysis. With international representation from Europe, Latin America, North America, and the Asia Pacific region, the team first collated common practices and guidance recommendations and assessed their suitability from both a scientific and logistical perspective. Subsequently, team members developed best practice recommendations and refined them through discussions and presentations with industry experts at scientific meetings. This review summarizes the team findings and best practice recommendations. The few topics where no consensus could be reached are also discussed. The A7 HT recommendations, together with those from the other GBC teams, provide the basis for future international harmonization of regulated bioanalytical practices.

Simultaneous quantification of purine and pyrimidine bases, nucleosides and their degradation products in bovine blood plasma by high performance liquid chromatography tandem mass spectrometry

Improved nitrogen utilization in cattle is important in order to secure a sustainable cattle production. As purines and pyrimidines (PP) constitute an appreciable part of rumen nitrogen, an improved understanding of the absorption and intermediary metabolism of PP is essential. The present work describes the development and validation of a sensitive and specific method for simultaneous determination of 20 purines (adenine, guanine, guanosine, inosine, 2'-deoxyguanosine, 2'-deoxyinosine, xanthine, hypoxanthine), pyrimidines (cytosine, thymine, uracil, cytidine, uridine, thymidine, 2'-deoxyuridine), and their degradation products (uric acid, allantoin, β-alanine, β-ureidopropionic acid, β-aminoisobutyric acid) in blood plasma of dairy cows. The high performance liquid chromatography-based technique coupled to electrospray ionization tandem mass spectrometry (LC-MS/MS) was combined with individual matrix-matched calibration standards and stable isotopically labelled reference compounds. The quantitative analysis was preceded by a novel pre-treatment procedure consisting of ethanol precipitation, filtration, evaporation and reconstitution. Parameters for separation and detection during the LC-MS/MS analysis were investigated. It was confirmed that using a log-calibration model rather than a linear calibration model resulted in lower CV% and a lack of fit test demonstrated a satisfying linear regression. The method covers concentration ranges for each metabolite according to that in actual samples, e.g. guanine: 0.10-5.0 μmol/L, and allantoin: 120-500 μmol/L. The CV% for the chosen quantification ranges were below 25%. The method has good repeatability (CV%≤25%) and intermediate precision (CV%≤25%) and excellent recoveries (91-107%). All metabolites demonstrated good long-term stability and good stability within-runs (CV%≤10%). Different degrees of absolute matrix effects were observed in plasma, urine and milk. The determination of relative matrix effects revealed that the method was suitable for almost all examined PP metabolites in plasma drawn from an artery and the portal hepatic, hepatic and gastrosplenic veins and, with a few exceptions, also for other species such as chicken, pig, mink, human and rat.

Bioanalytical chromatographic method validation according to current regulations, with a special focus on the non-well defined parameters limit of quantification, robustness and matrix effect

Method validation is a mandatory step in bioanalysis, to evaluate the ability of developed methods in providing reliable results for their routine application. Even if some organisations have developed guidelines to define the different parameters to be included in method validation (FDA, EMA); there are still some ambiguous concepts in validation criteria and methodology that need to be clarified. The methodology to calculate fundamental parameters such as the limit of quantification has been defined in several ways without reaching a harmonised definition, which can lead to very different values depending on the applied criterion. Other parameters such as robustness or ruggedness are usually omitted and when defined there is not an established approach to evaluate them. Especially significant is the case of the matrix effect evaluation which is one of the most critical points to be studied in LC-MS methods but has been traditionally overlooked. Due to the increasing importance of bioanalysis this scenario is no longer acceptable and harmonised criteria involving all the concerned parties should be arisen. The objective of this review is thus to discuss and highlight several essential aspects of method validation, focused in bioanalysis. The overall validation process including common validation parameters (selectivity, linearity range, precision, accuracy, stability…) will be reviewed. Furthermore, the most controversial parameters (limit of quantification, robustness and matrix effect) will be carefully studied and the definitions and methodology proposed by the different regulatory bodies will be compared. This review aims to clarify the methodology to be followed in bioanalytical method validation, facilitating this time consuming step.

ISR: background, evolution and implementation, with specific consideration for ligand-binding assays

ISR was highlighted as a topic of major interest to the US FDA in 2006, having been previously required, then discontinued, by Canadian regulatory authorities. Following an FDA focus on ISR, this topic has also been emphasized by regulatory agencies in Europe, Asia and Latin America. Extensive discussions on proper implementation of programs have taken place in multiple settings, including pharmaceutical companies, regulatory agencies, professional associations and CROs. These efforts have led to recommendations for ISR conduct that are now included in a final guideline on bioanalytical method validation from the European Medicines Agency, a draft validation guidance from the Ministry of Health, Labor and Welfare in Japan and a revised draft validation guidance from the FDA. In this Review we look at the background, evolution and implementation of ISR for all assays, while including some specific considerations on this topic for ligand-binding assays.

Detection and validated quantification of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, tadalafil, and 2 of their metabolites in human blood plasma by LC-MS/MS--application to forensic and therapeutic drug monitoring cases

INTRODUCTION

Phosphodiesterase type 5 inhibitors such as sildenafil, vardenafil, and tadalafil are a class of drugs used primarily in the treatment of erectile dysfunction. Sildenafil and tadalafil are also approved for the treatment of pulmonary hypertension. The aim of this study was to develop and validate a procedure for the detection and quantification of these 3 drugs and some of their metabolites in human blood plasma.

METHODS

After liquid-liquid extraction of 0.5 mL of blood plasma using diethyl ether-ethyl acetate (1:1), the analytes sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil were separated using a Shimadzu Prominence High-Performance Liquid Chromatography System (C18 separation column, gradient elution, and a total flow of 0.5 mL/min). They were detected using an AB Sciex 3200 Q-Trap LC-MS-MS System (electrospray ionization and multiple reaction monitoring mode). The method was fully validated according to international guidelines.

RESULTS

The assay was found to be selective for the tested compounds. It was linear from 5 to 1000 ng/mL for sildenafil, from 2 to 700 ng/mL for norsildenafil, from 0.5 to 350 ng/mL for vardenafil, from 0.5 to 200 ng/mL for norvardenafil, and from 5 to 1000 ng/mL for tadalafil. The recoveries were generally more than 50%. Matrix effects were not observed. Accuracy, repeatability, and intermediate precision were within the required limits (<15% or <20% near the limit of quantification). No instability was observed after repeated freezing and thawing or in processed samples.

CONCLUSIONS

A liquid chromatography-tandem mass spectrometry assay for the determination of sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil in human blood plasma was developed and validated. It has proven to be selective, linear, accurate, and precise for all studied drugs. The method has also proven to be applicable for forensic cases and for therapeutic drug monitoring.