Development and validation of an HPLC–MS/MS method to determine clopidogrel in human plasma. Use of incurred samples to test back-conversion

Selective and Sensitive UHPLC Method for the Trace Analysis of Formaldehyde in Drug Substance Using Fused-core Column Technology and Detailed Pre-column Derivatization study

Background:

Formaldehyde is a key intermediate/reagent in the synthesis of many significant pharmaceutical compounds. It is genotoxic as it interacts with the DNA, RNA and hence there is a pressing need to develop sensitive analytical methods for its trace level determination.

Objective:

The present study aims to develop a simple and robust Ultra-High-Performance Liquid Chromatographic (UHPLC) method for the trace level quantification of a carcinogen-formaldehyde, in pharmaceutical drug substance.

Methods:

This method was developed on a conventional pre-column derivatization technique with brady’s reagent followed by fast analysis on fused core C18 Ascentis Express (150 × 4.6 mm, 2.7 μm) column using ultraviolet (UV) detection. Optimization of the derivatization reaction time was conducted in different pH conditions. The optimized analytical method was fully validated in accordance with the current International Conference on Harmonization (ICH) Q2 guidelines, which demonstrated the developed method to be fast, specific, linear, sensitive, repeatable, accurate and convenient for routine quality control.

Results:

The developed method was linear, accurate and precise in the concentration of 12.8 ng/mL to 510.7 ng/mL. The LOD and LOQ were found to be 3.8 ng/mL and 12.8 ng/mL, respectively.

Conclusion:

The developed UHPLC can be used effectively for trace level quantification of formaldehyde in drug substances or drug products.

A Review of Analytical Methods for the determination of Clopidogrel in Pharmaceuticals and Biological Matrices

P2Y12 belongs to a group of G protein-coupled (GPCR) purinergic receptors and is a receptor for adenosine diphosphate (ADP). The P2Y12 receptor is involved in platelet aggregation and acts as a biological target for treating thromboembolisms and other clotting disorders. The use of Clopidogrel (CLO) has improved the morbidity and mortality endpoints including cardiovascular death, recurrent myocardial infarction (MI) and stroke at 30 days after percutaneous coronary intervention (PCI). CLO is one such drug that specifically and irreversibly inhibits the P2Y12 subtype of ADP receptor. This review delivers a detail description of various analytical methods published for the estimation of CLO and its combinations in pharmaceuticals and biological matrices. The review highlights the basic as well as advanced techniques performed for estimating CLO. The most commonly used assay techniques were UV and Visible spectrophotometry, high performance liquid chromatography (HPLC), high performance thin layer chromatography (HPTLC), micellar liquid chromatography (MLC), micellar electro kinetic chromatography (MEKC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Despite other analytical methods employed for the assay of CLO, the review reveals that the technique of HPLC with UV detection was widely used.

Evaluation of Clopidogrel Conjugation Metabolism: PK Studies in Man and Mice of Clopidogrel Acyl Glucuronide

The existence of a glucuronide conjugate of the major circulating clopidogrel metabolites, called clopidogrel acyl glucuronide (CAG), is already known. However, information regarding its pharmacokinetics (PK), metabolism, and clearance are modest. We investigated in vivo the potential CAG trans-esterification to clopidogrel (reaction occurring in vitro in particular conditions) by administering the metabolite to mice. Experiments were then carried out on men, clopidogrel administered alone or followed by activated charcoal intake (intestinal reabsorption blockade). Study objectives included: PK comparison of CAG, clopidogrel carboxylic acid (CCA), and clopidogrel in plasma, determination of their elimination patterns in urine and feces, and tracking of charcoal-induced changes in PK and/or urinary excretion that would indicate relevant enterohepatic recycling of CAG. In mice, CAG was rapidly hydrolyzed to CCA after oral administration, whereas by intravenous route metabolic conversion to CCA was delayed. No levels of clopidogrel were detected in mice plasma, excluding any potential trans-esterification or other form of back-conversion in vivo. PK experiments in man showed that CAG is hydrolyzed in the gastrointestinal tract (very low concentrations in feces), but there is no evidence of enterohepatic recirculation. Quantitation of the three moieties in stool samples accounted for only 1.2% of an administered dose, suggesting that other yet unknown metabolites/degradation products formed through metabolic processes and/or the activity of local microflora are mainly excreted by this route. In man CAG was confirmed as one of the major terminal metabolites of clopidogrel, with a PK behavior similar to CCA.

Development of a sensitive and fast UHPLC-MS/MS method for determination of clopidogrel, clopidogrel acid and clopidogrel active metabolite H4 in human plasma

BACKGROUND

Quantitation of CAM H4 in biological matrix has been a challenge due to low concentrations, instability and the existence of four CAM diastereomers. Historically, either inactive clopidogrel acid or CAM diastereomers without separation were measured for exposure and PK parameters.

RESULTS

This study presents a sensitive and fast UHPLC-MS/MS method for simultaneous quantitation of clopidogrel, clopidogrel acid and active metabolite H4 in human plasma. The method demonstrated the separation of H4 from other isomers and yet retained clopidogrel acid. Matrix stabilities, accuracy and precision, recovery and matrix effect were evaluated during development.

CONCLUSION

With LLOQ of 0.05 ng/ml for clopidogrel and H4, and 5.5 min LC gradient, it is the most sensitive and fastest method to our knowledge.

Development and validation of an HPLC-MS/MS method to determine clopidogrel in human plasma

A quantitative method for clopidogrel using online-SPE tandem LC–MS/MS was developed and fully validated according to the well-established FDA guidelines. The method achieves adequate sensitivity for pharmacokinetic studies, with lower limit of quantifications (LLOQs) as low as 10 pg/mL. Chromatographic separations were performed on reversed phase columns Kromasil Eternity-2.5-C18-UHPLC for both methods. Positive electrospray ionization in multiple reaction monitoring (MRM) mode was employed for signal detection and a deuterated analogue (clopidogrel-d₄) was used as internal standard (IS). Adjustments in sample preparation, including introduction of an online-SPE system proved to be the most effective method to solve the analyte back-conversion in clinical samples. Pooled clinical samples (two levels) were prepared and successfully used as real-sample quality control (QC) in the validation of back-conversion testing under different conditions. The result showed that the real samples were stable in room temperature for 24 h. Linearity, precision, extraction recovery, matrix effect on spiked QC samples and stability tests on both spiked QCs and real sample QCs stored in different conditions met the acceptance criteria. This online-SPE method was successfully applied to a bioequivalence study of 75 mg single dose clopidogrel tablets in 48 healthy male subjects.

Development and Validation of an HPLC Method for Simultaneous Quantification of Clopidogrel Bisulfate, Its Carboxylic Acid Metabolite, and Atorvastatin in Human Plasma: Application to a Pharmacokinetic Study

A simple, sensitive, and specific reversed phase liquid chromatographic method was developed and validated for simultaneous quantification of clopidogrel, its carboxylic acid metabolite, and atorvastatin in human serum. Plasma samples were deproteinized with acetonitrile and ibuprofen was chosen as internal standard. Chromatographic separation was performed on an BDS Hypersil C18 column (250 × 4.6 mm; 5 μm) via gradient elution with mobile phase consisting of 10 mM phosphoric acid (sodium) buffer solution (pH = 2.6 adjusted with 85% orthophosphoric acid) : acetonitrile : methanol with flow rate of 1 mL·min(-1). Detection was achieved with PDA detector at 220 nm. The method was validated in terms of linearity, sensitivity, precision, accuracy, limit of quantification, and stability tests. Calibration curves of the analytes were found to be linear in the range of 0.008-2 μg·mL(-1) for clopidogrel, 0.01-4 μg·mL(-1) for its carboxylic acid metabolite, and 0.005-2.5 μg·mL(-1) for atorvastatin. The results of accuracy (as recovery) with ibuprofen as internal standard were in the range of 96-98% for clopidogrel, 94-98% for its carboxylic acid metabolite, and 90-99% for atorvastatin, respectively.

Analysis of imprecision in incurred sample reanalysis for small molecules

Over the years, incurred sample (IS) reanalysis (ISR) has become a tool to confirm the reliability of bioanalytical measurements. The recommendation for ISR acceptance criterion for small molecules is at least 67% of ISR samples that have reanalyzed concentrations within 20% of their original concentrations when normalized to their means. To understand the relevance of the ISR acceptance criterion and sample size requirements, simulated ISR studies evaluated the probability of ISR studies passing the acceptance criterion (ISR pass rate) as a function of IS imprecision and sample size. When IS imprecision (percent coefficient of variation: %CV) is low (≤ 10 or 1-10% CV), high ISR pass rate (≥ 99%) is attained with <50 samples. At intermediate IS imprecision (e.g., 12% CV or 7-12% CV range), 80-160 samples are required for a high ISR pass rate. When IS imprecision is at the higher end of the acceptance limit, ISR pass rate decreases significantly, and increasing sample size fails to achieve high ISR pass rate. The effect of systematic bias (e.g., instability, interconversion) on ISR pass rate is strongly dependent on sample size at intermediate IS imprecision. The results provide an understanding of the effect of IS imprecision on ISR pass rates and a framework for selection of ISR sample sizes.

Comparison of a solid SMEDDS and solid dispersion for enhanced stability and bioavailability of clopidogrel napadisilate

The intention of this study was to compare the physicochemical properties, stability and bioavailability of a clopidogrel napadisilate (CN)-loaded solid dispersion (SD) and solid self-microemulsifying drug delivery system (solid SMEDDS). SD was prepared by a surface attached method using different ratios of Cremophor RH60 (surfactant) and HPMC (polymer), optimized based on their drug solubility. Liquid SMEDDS was composed of oil (peceol), a surfactant (Cremophor RH60) and a co-surfactant (Transcutol HP). A pseudo-ternary phase diagram was constructed to identify the emulsifying domain, and the optimized liquid SMEDDS was spray dried with an inert solid carrier (silicon dioxide), producing the solid SMEDDS. The physicochemical properties, solubility, dissolution, stability and pharmacokinetics were assessed and compared to clopidogrel napadisilate (CN) and bisulfate (CB) powders. In solid SMEDDS, liquid SMEDDS was absorbed or coated inside the pores of silicon dioxide. In SD, hydrophilic polymer and surfactants were adhered onto drug surface. The drug was in crystalline and molecularly dispersed form in SD and solid SMEDDS, respectively. Solid SMEDDS and SD greatly increased the solubility of CN but gave lower drug solubility compared to CB powder. These preparations significantly improved the dissolution of CN, but the latter more increased than the former. Stability under accelerated condition showed that they were more stable compared to CB powder, and SD was more stable than solid SMEDDS. They significantly increased the oral bioavailability of CN powder. Furthermore, SD showed significantly improved oral bioavailability compared to solid SMEDDS and CB powder. Thus, SD with excellent stability and bioavailability is recommended as an alternative for the clopidogrel-based oral formulation.

Determination of duloxetine in human plasma with proven lack of influence of the major metabolite 4-hydroxyduloxetine

OBJECTIVES

Minimizing the impact of major or unstable metabolites on the determination of a drug substance represents a leading task in the development and validation of bioanalytical methods. "Incurred samples reanalysis" provides relevant information too late; therefore, carefully selected tests on known metabolites should precede the pharmacokinetic studies.

DESIGN AND METHODS

This paper describes a simple and rapid HPLC-UV method for the determination of duloxetine, a potent serotonin and norepinephrine reuptake inhibitor, in the presence of its major metabolite, i.e. 4-hydroxyduloxetine glucuronide. Analyte and fluoxetine (internal standard) were extracted from human plasma by liquid-liquid extraction.

RESULTS

No influence of the major metabolite was observed on the reliability of the new method. There was also lack of evidence of the major metabolite back-conversion to the parent drug substance. The validation demonstrated high precision of the new method. All validation parameters met the acceptance criteria of bioanalytical regulations.

CONCLUSIONS

The new method enabled the reliable determination of duloxetine in the presence of its major metabolite in the human plasma. The method might be applied to pharmacokinetic studies in humans, including bioequivalence and therapeutic drug monitoring.

Quantitative determination of clopidogrel and its metabolites in biological samples: a mini-review

Clopidogrel has been applied in antiplatelet therapy since 1998 and is the thienopyridine with the largest clinical experience. By 2011, clopidogrel (Plavix(®)) was the second top-selling drug in the world. Following complete patent expiry in 2012/2013 its use is expected to grow even further from generics entering the market. Prefaced by a brief description of clopidogrel metabolism, this review analyzes analytical methods addressing the quantification of clopidogrel and its metabolites in biological samples. Techniques that have been applied to analyze human plasma or serum are predominantly LC-MS and LC-MS/MS. The lowest level of clopidogrel quantification that has been achieved is 5pg/mL, the shortest runtime is 1.5min and almost 100% recovery has been reported using solid-phase extraction for sample preparation.

Recent advances in bioanalytical sample preparation for LC-MS analysis

Sample preparation has historically been, and continues to be, the most challenging part of the bioanalytical workflow. Several techniques have been developed over the years to deal with the problems of recovery and matrix effects in an effort to increase the reliability and robustness of the bioanalytical method. In recent years certain techniques have come into prominence and gained acceptance in routine sample preparation, and some have shown promise in their use in a discovery environment where speed is critical and method development time is often limited. The aim of this review is to examine several of these techniques and provide examples of their use from the literature, as well as comment on their utility in current workflows.

A sensitive and rapid ultra HPLC-MS/MS method for the simultaneous detection of clopidogrel and its derivatized active thiol metabolite in human plasma

A sensitive, selective, and rapid ultra-high performance liquid chromatography-tandem mass spectrometry (uHPLC-MS/MS) was developed for the simultaneous quantification of clopidogrel (Plavix(®)) and its derivatized active metabolite (CAMD) in human plasma. Derivatization of the active metabolite in blood with 2-bromo-3'-methoxy acetophenone (MPB) immediately after collection ensured metabolite stability during sample handling and storage. Following addition of ticlopidine as an internal standard and simple protein precipitation, the analytes were separated on a Waters Acquity UPLC™ sub-2 μm-C(18) column via gradient elution before detection on a triple-quadrupole MS with multiple-reaction-monitoring via electrospray ionization. The method was validated across the clinically relevant concentration range of 0.01-50 ng/mL for parent clopidogrel and 0.1-150 ng/mL (r(2)=0.99) for CAMD, with a fast run time of 1.5 min to support pharmacokinetic studies using 75, 150, or 300 mg oral doses of clopidogrel. The analytical method measured concentrations of clopidogrel and CAMD with accuracy (%DEV) <±12% and precision (%CV) of <±6%. The method was successfully applied to measure the plasma concentrations of clopidogrel and CAMD in three subjects administered single oral doses of 75, 150, and 300 mg clopidogrel. It was further demonstrated that the derivatizing agent (MPB) does not affect clopidogrel levels, thus from one aliquot of blood drawn clinically, this method can simultaneously quantify both clopidogrel and CAMD with sensitivity in the picogram per mL range.

Incurred sample reanalysis: different evaluation approaches on data obtained for spironolactone and its active metabolite canrenone

Background: The inherent reproducibility of a bioanalytical approach is usually sustained through incurred sample reanalysis (ISR). Questions relating to the number of ISRs, the right moment for performing reanalysis, the way of performing an appropriate statistical refinement of experimental data and actions to be taken in the case of failure are frequently raised. Results: Data resulting from ISR following a bioequivalence study for spironolactone formulations are discussed. Reanalysis of samples was carried out twice: immediately after the end of the study and after a period that overcame the long-term stability study achieved during method validation. The Bland–Altman approach was used to assess experimental results. ISR was successful over the short reanalysis period for both compounds. Data produced through reanalysis after the long-term period indicated a systematic positive bias for the metabolite canrenone (although results supported reproducibility). The results obtained for spironolactone were affected by a strong negative systematic bias and failed to support reproducibility. The explanation deals with the continuous conversion of spironolactone to canrenone in plasma samples. However, reproducibility of the method may be sustained by comparing original and repeated differences between concentration values in samples by means of a paired t-test, Wilcoxon sign rank-sum test and linear regression. Conclusions: Different statistical approaches for making data comparisons are discussed and may be successfully applied during reanalysis of samples from a bioequivalence study. Results of the evaluations may differ in accordance with the statistical procedure being applied, thus a definitive conclusion requires consideration of all specific experimental circumstances arising during production of the processed data.

Incurred sample reanalysis (ISR): a decisive tool in bioanalytical research

The AAPS Workshop 2008 on Current Topics in GLP Bioanalysis: Assay Reproducibility for Incurred Samples was the defining moment in establishing incurred sample reanalysis (ISR) as a mandatory exercise in demonstrating assay reproducibility using incurred (study) samples. The importance of ISR can be envisaged from its role in clinical as well as non-clinical studies. Incurred samples can differ significantly in their composition when compared with the calibration standards and quality control samples that are used to validate the developed method. The present article attempts to summarize five troubleshooting cases encountered in the analyses of incurred samples for bioanalytical methods developed in our laboratory for mesalamine, hydrochlorothiazide, clopidogrel, sildenafil and rabeprazole. The issues identified were related to: sample inhomogeneity, sample processing error, impact of buffer pH during sample preparation, instability of metabolite and change in laboratory environment. The steps taken to trace and correct these incidents are discussed with adequate data. These examples will further broaden the scope and emphasize the significance of ISR. We believe this investigation will help to develop more reliable and efficient bioanalytical methods.