First-in-human study of CPL207280, a novel G-protein-coupled receptor 40/free fatty acid receptor 1 agonist, in healthy volunteers after single and multiple administration.

AIM: To assess the safety, tolerability and pharmacokinetic (PK) profile of single and multiple doses of CPL207280, a new G-protein-coupled receptor 40 agonist developed to treat type 2 diabetes (T2D). METHODS: The phase 1 study in healthy volunteers (White, age 18-55 years, body mass index 18.5-29.9 kg/m2 ) was performed after single (24 subjects, 5-480 mg) and multiple (32 subjects, 60-480 mg) once-daily administration of CPL207280.  The effect of food intake and interaction with metformin were evaluated in additional cohort (12 subjects, 120 mg). The primary objective was the safety and tolerability of CPL207280. Secondary objectives included PK and pharmacodynamic (PD) characteristics (glucose, insulin, C-peptide, proinsulin, glucagon levels) observed during the 14-day treatment period. RESULTS: No deaths or serious adverse events (AEs) were reported. All reported AEs were classified as unrelated to the study product. No clinically significant differences in safety parameters were observed between cohorts and no food or metformin effect on safety parameters was identified. The ascending dose of CPL207280 caused an increase in the PK parameters maximum observed plasma concentration (Cmax ) or area under the plasma concentration-time curve up to 24 h. However, dose-normalized Cmax decreased with ascending dose. There was no relationship between the CPL207280 dose or prandial state and terminal elimination half-life and terminal elimination rate constant. No clear relationship between CPL207280 dose and PD area under the effect curve values was observed. CONCLUSIONS: CPL207280 was found to be safe and well tolerated by healthy volunteers (with a low risk of hepatotoxicity) for up to 14 days of administration. The PK profile of CPL207280 supports single-daily administration and justifies further development of this therapy for patients with T2D.

Replicates Number for Drug Stability Testing during Bioanalytical Method Validation-An Experimental and Retrospective Approach.

BACKGROUND: The stability of a drug or metabolites in biological matrices is an essential part of bioanalytical method validation, but the justification of its sample size (replicates number) is insufficient. The international guidelines differ in recommended sample size to study stability from no recommendation to at least three quality control samples. Testing of three samples may lead to results biased by a single outlier. We aimed to evaluate the optimal sample size for stability testing based on 90% confidence intervals. METHODS: We conducted the experimental, retrospective (264 confidence intervals for the stability of nine drugs during regulatory bioanalytical method validation), and theoretical (mathematical) studies. We generated experimental stability data (40 confidence intervals) for two analytes-tramadol and its major metabolite (O-desmethyl-tramadol)-in two concentrations, two storage conditions, and in five sample sizes (n = 3, 4, 5, 6, or 8). RESULTS: The 90% confidence intervals were wider for low than for high concentrations in 18 out of 20 cases. For n = 5 each stability test passed, and the width of the confidence intervals was below 20%. The results of the retrospective study and the theoretical analysis supported the experimental observations that five or six repetitions ensure that confidence intervals fall within 85-115% acceptance criteria. CONCLUSIONS: Five repetitions are optimal for the assessment of analyte stability. We hope to initiate discussion and stimulate further research on the sample size for stability testing.

10th Anniversary of a Two-Stage Design in Bioequivalence. Why Has it Still Not Been Implemented?

PURPOSE: In 2010 the European Medicines Agency allowed a two-stage design in bioequivalence studies. However, in the public domain there are mainly articles describing the theoretical and statistical base for the application of the two-stage design. One of the reasons seems to be the lack of practical guidance for the Sponsors on when and how the two-stage design can be beneficial in bioequivalence studies. METHODS: Different variants with positive and negative outcomes have been evaluated, including a pivotal study, pilot + pivotal study and two-stage study. The scientific perspective on the two-stage bioequivalence study has been confronted with the industrial one. RESULTS: Key information needed to conduct a bioequivalence study - such as in vitro data and pharmacokinetics - have been listed and organized into a decision scheme. Advantages and disadvantages of the two-stage design have been summarized. CONCLUSION: The use of the two-stage design in bioequivalence studies seems to be a beneficial alternative to the 2 × 2 crossover study. Basic information on the properties of the active substance and the characteristics of the drug form are needed to make an initial decision to carry out the two-stage study.

ENVIRONMENTALLY FRIENDLY LC/MS DETERMINATION OF EPLERENONE IN HUMAN PLASMA.

Eplerenone (EPL), a selective aldosterone receptor antagonist, is indicated in the treatment of chronic heart failure and hypertension. It is hard to find a green assay among a few published methods for its determination in human plasma or serum. Following a liquid-liquid extraction with methyl t-butyl ether, eplerenone and isotope labelled eplerenone - used as an internal standard - were separated from the endogenous compounds on an Atlantis dCl8 column (150 x 3 mm, 3.0 [im). An isocratic elution with the mobile phase consisting of methanol and ammonium acetate (3 : 2, v/v) was used. A single quadrupole mass spectrometer was operated in positive electrospray ionization using the selected ion monitoring mode. The method is more environmentally-friendly than the previously reported assays. Acetonitrile in the mobile phase was replaced with methanol which is a removable solvent. Plasma sample volume was reduced to 250 pL which significantly decreased waste volume. Chlorinated solvents used previously for liquid-liquid extraction were eliminated and the safety of the laboratory staff was increased by eliminating diethyl ether. The method is characterized by a short analysis time, simple sample preparation and reduction of waste volume, which are important advantages when analyzing large numbers of samples. The method was validated according to international regulatory guidelines and may be applied to human pharmacokinetic studies following a single 25 or 50 mg oral dose.

HPLC-UV ASSAY OF IMATINIB IN HUMAN PLASMA OPTIMIZED FOR BIOEQUIVALENCE STUDIES.

lmatimb is an anticancer drug approved for the treatment of a number of cancers, mostly used in chronic myeloid leukemia. Numerous bioanalytical methods using high performance liquid chromatography coupled to ultraviolet detection point at the importance and necessity of the therapeutic drug monitoring of imatinib. Unfortunately, these methods are not optimized for single dose pharmacokinetic studies such as bioe- quivalence. In this study, attention was turned mostly to the analysis time, linearity range and interferences by endogenous components of the matrix and exogenous substances - especially metabolites. The method enables the quantification of imatinib in the presence of the main metabolite (N-desmethyl imatinib). Its potential back- conversion was examined during storage for 4 h at ambient temperature as well as for 239 days at -20°C. The sample preparation based on the liquid-liquid extraction was combined with a short analysis time of 7 min. Therefore, the method was suitable for analyzing large numbers of samples in a short time. The linearity range of 40-4000 ng/mL was optimized for human pharmacokinetic studies after a single 400 mg oral dose of ima- tinib. Successful application in a bioequivalence study confirmed the reliability of the method.

Determination of sunitinib in human plasma using liquid chromatography coupled with mass spectrometry.

An original method based on liquid chromatography with single quadrupole electrospray ionization mass spectrometry was developed for the determination of sunitinib in human plasma. The quantitation limit of the method at 0.10 ng/mL is comparable to that of tandem mass spectrometry assays. The handling of all solutions containing sunitinib was performed under low-intensity red light to avoid the isomerization of sunitinib and enable quantitation using a single peak. Liquid-liquid extraction with a mixture of n-hexane/isopropanol (90:10 v/v) allowed recoveries at the level of 70%. Measurements were performed using a Zorbax SB-C18 column (3.0 mm × 150 mm, 3.5 µm) and isocratic elution with (A) 0.1% aqueous formic acid and (B) acetonitrile/methanol (80:20 v/v) in an A/B ratio of 55:45 at 35°C. Under these conditions, sunitinib is eluted at 3.8 min in 6 min of the total run time. The linearity of the calibration curve ranges from 0.10 to 150 ng/mL. The baseline separation of sunitinib and its primary metabolite, N-des-ethyl sunitinib (SU12662), as well as sharp peak shapes, suggest a possibility of extending the applied methodology to the quantitative determination of both compounds. Isotopically labeled sunitinib was used as the internal standard. All required validation tests met the acceptance criteria and proved the method's reliability and robustness. The method may be conveniently applied to study the pharmacokinetics of sunitinib in humans.

Sensitive single quadrupole LC/MS method for determination of lapatinib in human plasma.

A sensitive liquid chromatographic-single quadrupole mass spectrometric method was developed and validated for the determination of lapatinib in human plasma. Following a liquid-liquid extraction with methyl t-butyl ether, lapatinib and isotope labelled lapatinib, used as an internal standard (IS), were separated from the endogenous compounds on a Zorbax SB-C18 (150 x 3 mm, 3.5 µm) column. An isocratic elution with the mobile phase consisting of formic buffer and the mixture of acetonitrile, methanol and formic acid was used. Mass spectrometry with positive electrospray ionization in a single ion monitoring mode was applied. The proposed method provides the satisfactory recovery of lapatinib from human plasma and a sensitivity comparable to numerous tandem mass spectrometric methods, with a lower limit of quantification of 5 ng/mL. The validated method may be applied to pharmacokinetic studies in humans following a single 250 mg oral dose.

How does the order of sample analysis influence the matrix effect during LC-MS bioanalysis?

Mass spectrometry coupled with liquid chromatography is a valuable tool for drug development and personalised drug therapy. The matrix effect is caused by enhancing or suppressing the analyte signal intensity by the interfering compounds of biological fluids. The matrix effect may influence the reliability of the quantitative results. Thus, its evaluation is a critical part of bioanalytical method validation. Identified factors affecting the matrix effect are the physicochemical properties of the analyte, type of biological material, analytical conditions, the ion source construction and calculation method. The order of analysis of test samples (pure solutions and post-extraction spiked samples) is another factor possibly affecting quantifying the matrix effect variability between sources. Our primary goal was to find which experimental design - interleaved or set of blocks - is more sensitive to detect matrix effect variability. Additionally, to better understand the reason of variability, we evaluated the influence of chromatographic elution and the type of plasma (normal, lipemic or hemolyzed), co-elution, and carry-over of phospholipids. We used chemometric methods: Principal Component Analysis and Partial Least-Squares Discriminant Analysis. Although a comparable (but statistically different) matrix effect (%RSDMF) is observed using the interleaved and block schemes, for some compounds, the order of the samples strongly influences the results. The interleaved scheme was generally more sensitive in detecting the matrix effect than the block scheme. Thus, reporting the order of samples is needed to ensure the repeatability of experiments. Chemometrics suggests that lipemic samples analyzed in isocratic conditions are most prone to the matrix effect. Different compositions of matrix lots of the same type - especially lipemic - may influence method reliability. Thus, evaluating more than one source of lipemic and hemolyzed plasma is recommended.

Bioequivalence and pharmacokinetics of two 10-mg bisoprolol formulations as film-coated tablets in healthy white volunteers: a randomized, crossover, open-label, 2-period, single-dose, fasting study.

OBJECTIVE: The aim of the study was to investigate the bioavailability of a generic formulation of 10-mg bisoprolol film coated tablets (test) as compared to that of a branded formulation (reference) at the same strength to determine bioequivalence and to apply for regulatory approval. The secondary objective of the study was to evaluate tolerability of both formulations. METHODS: A randomized, crossover, open-label, 2-period, single-dose, comparative study was conducted in healthy white volunteers in fasting conditions. A single oral dose administration of the test or reference formulation was followed by a 14-day wash-out period. Blood samples were collected up to 60 hours after dosing. The bisoprolol concentrations in plasma samples were determined using a validated LC-MS/MS method. The formulations were considered bioequivalent if 90% CI of geometric mean ratios (test/reference) for AUC0-t, AUC0-∞ and Cmax were within the range 80.00 - 25.00%. Adverse events were monitored throughout the study based on the clinical parameters and volunteer reports. RESULTS: Healthy male and female subjects participating in the study had a median (range) age of 23 (20 - 43), weight of 68 kg (52 - 84), height of 172 cm (157 - 184), and BMI of 23.1 kg/m2 (19.3 - 24.9). The 26 consented volunteers have been included and 24 of them completed the clinical part of the study. The geometric mean test/referenceratios (90% CI) for AUC0-t, AUC0-∞ and Cmax were 104.12% (100.52 - 107.85%), 104.05% (100.49 - 107.75%) and 107.91% (103.04 - 112.99%), respectively. All 90% CI were embraced by the 80.00 - 25.00% acceptance interval. No serious adverse events were reported. A total number of 6 non-serious, moderate adverse events were registered, including headache and vomiting in one subject. CONCLUSIONS: The results of the single-dose study in healthy white volunteers indicated that the film-coated tablets of Bisocard® 10 mg manufactured by ICN Polfa Rzeszów S.A. (test formulation) are bioequivalent to those of Concor 10® manufactured by Merck KGaA (reference formulation). Both formulations were well tolerated.

Validated HPLC method for determination of temozolomide in human plasma.

The aim of the study was to develop a bioanalytical method for the determination of temozolomide (TMZ) in human plasma. Plasma concentration of TMZ was determined on a C18 column after liquid-liquid extraction. Isocratic elution was applied with the mixture of aqueous acetic acid and methanol. Theophylline was used as the internal standard. To prevent chemical degradation of TMZ at physiological pH, plasma samples were acidified to pH < 3. All validation parameters met the acceptance criteria. Calibration curve, prepared using freshly spiked plasma samples, was linear within the range of 0.10-20.00 microg/mL. The method was found to be sufficiently accurate and precise over the studied range of concentrations. TMZ was stable in the acidified plasma samples for at least 50 days at < or = -14 degrees C and < or = -65 degrees C. The method recovery of TMZ from human plasma was consistent and ranged 37.1-41.1%. The developed method is suitable for pharmacokinetic studies in humans after oral administration of TMZ.

Bioequivalence study of 500 mg cefuroxime axetil film-coated tablets in healthy volunteers.

The aim of the study was to investigate the bioavailability of a generic product of 500 mg cefuroxime axetil film-coated tablets (test) as compared to that of a branded product (reference) at the same strength to determine bioequivalence and to apply for regulatory approval. The secondary objective of the study was to evaluate tolerability of both products. A double blinded, randomized, crossover, two-period, single-dose, comparative study was conducted in Caucasian healthy volunteers in fasting conditions. A single oral dose administration of the test or reference product was followed by 7-day wash-out period. The cefuroxime concentration was determined using a validated HPLC-UV method. The results of the single-dose study in healthy volunteers indicated that the film-coated tablets of Tarsime 500 mg manufactured by Tarchominskie Zaklady Farmaceutyczne Polfa S.A. (test product) are bioequivalent to those of Zinnat manufactured by GlaxoSmithKline Export Ltd. (reference product). Both products were well tolerated.

Evaluation of tramadol human pharmacokinetics and safety after co-administration of magnesium ions in randomized, single- and multiple-dose studies.

BACKGROUND: Magnesium ions (Mg2+) increase and prolong opioid analgesia in chronic and acute pain. The nature of this synergistic analgesic interaction has not yet been explained. Our aim was to investigate whether Mg2+ alter tramadol pharmacokinetics. Our secondary goal was to assess the safety of the combination. METHODS: Tramadol was administered to healthy Caucasian subjects with and without Mg2+ as (1) single 100-mg and (2) multiple 50-mg oral doses. Mg2+ was administered orally at doses of 150 mg and 75 mg per tramadol dosing in a single- and multiple-dose study, respectively. Both studies were randomized, open label, laboratory-blinded, two-period, two-treatment, crossover trials. The plasma concentrations of tramadol and its active metabolite, O-desmethyltramadol, were measured. RESULTS: A total of 25 and 26 subjects completed the single- and multiple-dose study, respectively. Both primary and secondary pharmacokinetic parameters were similar. The 90% confidence intervals for Cmax and AUC0-t geometric mean ratios for tramadol were 91.95-102.40% and 93.22-102.76%. The 90% confidence intervals for Cmax,ss and AUC0-τ geometric mean ratios for tramadol were 93.85-103.31% and 99.04-105.27%. The 90% confidence intervals for primary pharmacokinetic parameters were within the acceptance range. ANOVA did not show any statistically significant contribution of the formulation factor (p > 0.05) in either study. Adverse events and clinical safety were similar in the presence and absence of Mg2+. CONCLUSIONS: The absence of Mg2+ interaction with tramadol pharmacokinetics and safety suggests that this combination may be used in the clinical practice for the pharmacotherapy of pain.

Low-oxidation-potential thiophene-carbazole monomers for electro-oxidative molecular imprinting: Selective chemosensing of aripiprazole.

New thiophene-carbazole functional and cross-linking monomers electropolymerizing at potentials sufficiently low for molecular imprinting of an electroactive aripiprazole antipsychotic drug were herein designed and synthesized. Numerous conducting molecularly imprinted polymer (MIP) films are deposited by electropolymerization at relatively low potentials by electro-oxidation of pyrrole, aniline, phenol, or 3,4-ethylenedioxythiophene (EDOT). However, their interactions with templates are not sufficiently strong. Hence, it is necessary to introduce additional recognizing sites in these cavities to increase their affinity to the target molecules. For that, functional monomers derivatized with substituents forming stable complexes with the templates are used. However, oxidation potentials of these derivatives are often, disadvantageously, higher than that of parent monomers. Therefore, we designed and synthesized new functional and cross-linking monomers, which are oxidized at sufficiently low potentials. The deposited MIP and non-imprinted polymer (NIP) films were characterized by PM-IRRAS and UV-vis spectroscopy and imaged with AFM. The structure of the aripiprazole pre-polymerization complex with functional monomers was optimized with density functional theory (DFT), and aripiprazole interactions with imprinted cavities were simulated with molecular mechanics (MM) and molecular dynamics (MD). MIP-aripiprazole film-coated electrodes were used as extended gates for selective determination of aripiprazole with the extended-gate field-effect transistor (EG-FET) chemosensor. The linear dynamic concentration range was 30-300 pM, and the limit of detection was 22 fM. An apparent imprinting factor of the MIP-1 was IF = 4.95. The devised chemosensor was highly selective to glucose, urea, and creatinine interferences. The chemosensor was successfully applied for aripiprazole determination in human plasma. The results obtained were compared to those of the validated HPLC-MS method.

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.

Matrix effect screening for cloud-point extraction combined with liquid chromatography coupled to mass spectrometry: Bioanalysis of pharmaceuticals.

Matrix effects are one of the most challenging issues in the analysis of complex samples using liquid chromatography coupled to mass spectrometry (LC-MS). Apart from the instrumental origin, these effects are also related to sample preparation. Cloud-point extraction (CPE) is rarely combined with LC-MS as it requires the use of surfactants which might interfere with droplet evaporation. Thus, they are suspected to cause a significant matrix effect (signal suppression). In this paper, 73 model drugs with different physicochemical properties were screened to analyse how susceptible LC-MS is to the absolute and relative matrix effect (ME) when coupled with CPE for measurements in human plasma. Three combinations of the surfactant Triton X-114 concentration (1.5% or 6%) and extraction temperature (40 or 55 °C) in six pH values gave over 1300 analyte-sample preparation condition pairs. A new term - surfactant effect (calculated for the standard solution) - allowed us to distinguish between the surfactant effect and that related to interferences from human plasma. The screening revealed that CPE combined with LC-MS is not related to a significant ME in the optimal pH of extraction. A significant absolute ME (<85% or>115%) was observed only for 25% of the analytes. Data processing (principal component analysis, classification trees, partial least squares-discriminant analysis) based on the extraction conditions and molecular descriptors helped to identify compounds prone to the matrix effect and speed up method development. A low surfactant concentration and low temperature decreased both the absolute and relative ME. pH of the extraction influenced only the relative ME. Low retention time reduced the risk of relative ME, whereas high polarity and the possibility of hydrogen bond formation minimized the occurrence of the surfactant effect and absolute ME. A significant relative ME (>15%) was observed only for 11% of the compounds, thus CPE merged with LC-MS allowed to measure drug concentrations in a reliable manner for majority of compounds. The presented approach may be further applied to other analytes and matrices.

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.

Extended 3D and 4D cumulative plots for evaluation of unmatched incurred sample reanalysis.

AIM: Incurred sample reanalysis (ISR) helps ensure the reliability of pharmacokinetic studies. An appropriate graph may facilitate the evaluation of an unmatched reanalyses or a failed ISR test. METHODS: We evaluated different ways of visualizing multidimensional ISR data using an extended cumulative ISR plot. RESULTS: 3D and 4D cumulative ISR plots enable comprehensive data analysis using a single plot. We propose to use color for percentage difference classes in bar and XY-scatter plots. For the latter the shape of symbols may represent analyte concentration class, study phase, analyst or subject. CONCLUSION: The extended 3D and 4D cumulative ISR plots facilitate in-study monitoring and post-study inspection of data. It helps find the root cause of unmatched ISR, thus increasing reliability of bioanalytical data.

Quantitative evaluation of the matrix effect in bioanalytical methods based on LC-MS: A comparison of two approaches.

Liquid chromatography coupled to mass spectrometry (LC-MS) is a powerful tool for studying pharmacokinetics and toxicokinetics. Reliable bioanalysis requires the characterization of the matrix effect, i.e. influence of the endogenous or exogenous compounds on the analyte signal intensity. We have compared two methods for the quantitation of matrix effect. The CVs(%) of internal standard normalized matrix factors recommended by the European Medicines Agency were evaluated against internal standard normalized relative matrix effects derived from Matuszewski et al. (2003). Both methods use post-extraction spiked samples, but matrix factors require also neat solutions. We have tested both approaches using analytes of diverse chemical structures. The study did not reveal relevant differences in the results obtained with both calculation methods. After normalization with the internal standard, the CV(%) of the matrix factor was on average 0.5% higher than the corresponding relative matrix effect. The method adopted by the European Medicines Agency seems to be slightly more conservative in the analyzed datasets. Nine analytes of different structures enabled a general overview of the problem, still, further studies are encouraged to confirm our observations.

An overview of chromatographic methods coupled with mass spectrometric detection for determination of angiotensin-converting enzyme inhibitors in biological material.

Gas and liquid chromatography-mass spectrometry (GC-MS, LC-MS) methods for the determination of angiotensin-converting enzyme inhibitors (ACEIs) and their metabolites in biological material have been reviewed. Since 1980s those hyphenated techniques have been applied to quantitate ACE inhibitors and the dynamic increase in the number of relevant publications can be observed in recent years. Although most of the methods available in the literature were analyses of plasma or serum, assays of blood and urine were also included. Additionally, sample pretreatment methods, separation conditions and ionization modes were overviewed. Some information on chemical structures, cis-trans izomerization and stability of compounds in question was also included. Most of the reported methods were successfully applied to the pharmacokinetic studies in humans.

Comprehensive graphical presentation of data from incurred sample reanalysis.

AIM: Incurred sample reanalysis (ISR) contributes to the reliability of pharmacokinetic studies. Despite regulatory guidelines having adopted ISR methodology, graphical presentation of data has been overlooked. MATERIALS & METHODS: Different graphs were tested for datasets including limited, standard and large numbers of ISR pairs. The datasets covered both passed and failed cases. RESULTS: We have developed a combination of complementary plots enabling the visual inspection of ISR data quality: %difference versus mean concentration and cumulative ISR plot. The former shows individual ISR datapoints and concentration-dependent trends, while the latter presents the contribution of individual pairs to the overall result as well as time-dependent trends. CONCLUSION: The proposed visualization of ISR data shows at a glance whether acceptance criteria for each sample and whole experiment are met or not. Standardized graphical presentation of ISR outcomes may increase quality of bioanalytical data.