Manish Yadav

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.

Stability evaluation and sensitive determination of antiviral drug, valacyclovir and its metabolite acyclovir in human plasma by a rapid liquid chromatography–tandem mass spectrometry method

A simple, sensitive and high throughput liquid chromatography/positive-ion electrospray ionization mass spectrometry (LC-ESI-MS/MS) method has been developed for the simultaneous determination of valacyclovir and acyclovir in human plasma using fluconazole as internal standard (IS). The method involved solid phase extraction of the analytes and IS from 0.5 mL human plasma with no reconstitution and drying steps (direct injection of eluate). The chromatographic separation was achieved on a Gemini C18 analytical column using isocratic mobile phase, consisting of 0.1% formic acid and methanol (30:70 v/v), at a flow-rate of 0.8 mL/min. The precursor-->product ion transition for valacyclovir (m/z 325.2-->152.2), acyclovir (m/z 226.2-->152.2) and IS (m/z 307.1-->220.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) mode. The method was validated over the concentration range 5.0-1075 ng/mL and 47.6-10225 ng/mL for valacyclovir and acyclovir respectively. The mean recovery of valacyclovir (92.2%), acyclovir (84.2%) and IS (103.7%) from spiked plasma samples was consistent and reproducible. The bench top stability of valacyclovir and acyclovir was extensively evaluated in buffered and unbuffered plasma. It was successfully applied to a bioequivalence study in 41 healthy human subjects after oral administration of 1000 mg valacyclovir tablet formulation under fasting condition.

Comparison of extraction procedures for assessment of matrix effect for selective and reliable determination of atazanavir in human plasma by LC–ESI-MS/MS

A comparative study with three conventional extraction techniques namely protein precipitation (PP), liquid-liquid extraction (LLE) and solid phase extraction (SPE) has been demonstrated to assess the magnitude of matrix interference by post-column analyte infusion and post extraction analyte spiking for the determination of atazanavir from human plasma. Severe ion suppression observed in PP and to a lesser extent in LLE was circumvented by SPE on LiChrosep Sequence extraction cartridge. Based on these observations a selective, rugged and high throughput SPE-LC-MS/MS method has been developed for reliable determination of atazanavir in human plasma. The chromatographic separation was achieved on a Hypersil Gold C18 (50mm×4.6mm, 5μm) analytical column using 5mM ammonium formate in water:methanol (10:90, v/v) as the mobile phase under isocratic conditions. The method was validated over a wide dynamic concentration range of 10-6000ng/mL. The mean relative recovery and absolute matrix effect across quality controls were 84.9 and 93.2%, respectively. The precision value for relative matrix effect between eight different lots of plasma, expressed as %CV of the slopes of the calibration lines was 2.41. The stability of atazanavir under different storage conditions varied from -8.4 to 5.4%. The method was successfully applied to a bioequivalence study of 300mg atazanavir capsule formulation in 24 healthy Indian males under fasting condition.

Application of a rapid and selective method for the simultaneous determination of protease inhibitors, lopinavir and ritonavir in human plasma by UPLC-ESI-MS/MS for bioequivalence study in Indian subjects

A high throughput and rugged ultra performance liquid chromatography tandem mass spectrometry (UPLC-ESI-MS/MS) method is developed and validated for the selective determination of protease inhibitors -- lopinavir (LPV) and ritonavir (RTV) in human plasma. Plasma samples were prepared by solid phase extraction of the analytes and their deuterated analogs as internal standard (IS) using Waters Oasis HLB cartridges. The chromatographic separation was achieved in a run time of 1.2 min on Waters Acquity UPLC BEH C18 column (50 mm x 2.1 mm, 1.7 microm) under isocratic conditions. The mobile phase consisted of 10 mM ammonium formate, pH 4.0 adjusted with formic acid and methanol (10:90, v/v). The protonated precursor --> product ion transitions for lopinavir, ritonavir, d(8)-lopinavir and d(6)-ritonavir were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. A linear dynamic range of 2.9-1452 ng/mL and 29.6-14379 ng/mL was established for ritonavir and lopinavir respectively using 0.1 mL human plasma. The mean relative recovery of lopinavir (96.6%), ritonavir (97.5%), d(8)-lopinavir (85.5%) and d(6)-ritonavir (86.3%) from spiked plasma samples was consistent and reproducible. The method was successfully applied to a bioequivalence study of [200(lopinavir)+50(ritonavir)]mg tablet formulation in 36 healthy human subjects under fasting conditions.

Chromatographic separation and sensitive determination of teriflunomide, an active metabolite of leflunomide in human plasma by liquid chromatography-tandem mass spectrometry

A sensitive, selective and high throughput liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) method has been developed for the determination of teriflunomide, an active metabolite of leflunomide in human plasma. Plasma samples were prepared by liquid-liquid extraction of teriflunomide and valsartan as internal standard (IS) in ethyl acetate from 200microL human plasma. The chromatographic separation was achieved on an Inertsil ODS-3 C18 (50mmx4.6mm, 3microm) analytical column using isocratic mobile phase, consisting of 20mM ammonium acetate-methanol (25:75, v/v), at a flow-rate of 0.8mL/min. The precursor-->product ion transition for teriflunomide (m/z 269.0-->82.0) and IS (m/z 434.1-->350.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and negative ion mode. The method was validated over a wide dynamic concentration range of 10.1-4001ng/mL. Matrix effect was assessed by post-column infusion experiment and the mean process efficiency were 91.7% and 88.2% for teriflunomide and IS respectively. The method was rugged and rapid with a total run time of 2.0min and is applied to a bioequivalence study of 20mg leflunomide (test and reference) tablet formulation in 12 healthy Indian male subjects under fasting condition.

Sensitive, selective and rapid determination of bupropion and its major active metabolite, hydroxybupropion, in human plasma by LC-MS/MS: application to a bioequivalence study in healthy Indian subjects

A sensitive, selective and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of bupropion (BUP) and its major active metabolite hydroxybupropion (HBUP) in human plasma. Separation of both the analytes and venlafaxine as internal standard (IS) from 50 μL human plasma was carried out by solid-phase extraction. The chromatographic separation of the analytes was achieved on a Zorbax Eclipse XDB C(18) (150 × 4.6 mm, 5 µm) analytical column using isocratic mobile phase consisting of 20 mm ammonium acetate-methanol (10:90, v/v), with a resolution factor of 3.5. The method was validated over a wide dynamic concentration range of 0.1-350 ng/mL for BUP and 0.1-600 ng/mL for HBUP. The matrix effect was assessed by post-column infusion and the mean process efficiency was 96.08 and 94.40% for BUP and HBUP, respectively. The method was successfully applied to a bioequivalence study of 150 mg BUP (test and reference) extended release tablet formulation in 12 healthy Indian male subjects under fed conditions.

Chromatographic separation of (E)- and (Z)-isomers of entacapone and their simultaneous quantitation in human plasma by LC-ESI-MS/MS.

A selective, sensitive and high throughput liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for the chromatographic separation and quantitation of (E)-entacapone and (Z)-entacapone in human plasma. Sample clean-up involved liquid-liquid extraction (LLE) of both the isomers and carbamazepine used as internal standard from 500microL of human plasma. Both the analytes were chromatographically separated with a resolution factor of 3.0 on a Gemini C18 (50mmx4.6mm, 5microm particle size) analytical column using 1% formic acid and methanol (50:50, v/v) as the mobile phase. The selectivity factor (alpha) of the column for the separation was 2.0, based on the capacity factors of 2.6 and 1.3 for (E)- and (Z)-isomers respectively. The parent-->product ion transitions for both the isomers (m/z 306.1-->233.0) and IS (m/z 237.3-->194.2) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. The method was validated over the concentration range of 24.3-6076ng/mL and 23.8-5960ng/mL for (E)-entacapone and (Z)-entacapone respectively. Matrix effect was assessed by post-column analyte infusion experiment and the process/extraction efficiency found was 94.3% and 89.3% for (E)- and (Z)-isomers respectively. The method was successfully applied to a pivotal bioequivalence study in 36 healthy human subjects after oral administration of 200mg (E)-entacapone tablet formulation under fasting conditions.

Automated liquid-liquid extraction based on 96-well plate format in conjunction with ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for the quantitation of methoxsalen in human plasma.

A sensitive, specific and high throughput bioanalytical method using automated sample processing via 96-well plate liquid-liquid extraction and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) has been developed for the determination of methoxsalen in human plasma. Plasma samples with ketoconazole as internal standard (IS) were prepared by employing 0.2 mL human plasma in ethyl acetate:dichloromethane (80:20, v/v). The chromatographic separation was achieved on a Waters Acquity UPLC BEH C18 column using isocratic mobile phase, consisting of 10 mM ammonium formate and acetonitrile (60:40, v/v), at a flow rate of 0.5 mL/min. The linear dynamic range was established over the concentration range 1.1-213.1 ng/mL for methoxsalen. The method was rugged and rapid with a total run time of 1.5 min. It was successfully applied to a pivotal bioequivalence study in 12 healthy human subjects after oral administration of 10 mg extended release methoxsalen formulation under fasting condition.

Development of an SPE-LC-MS/MS method for simultaneous quantification of bosentan and its active metabolite hydroxybosentan in human plasma to support a bioequivalence study.

A highly sensitive, selective and rapid bioanalytical method has been developed for the simultaneous determination of bosentan and hydroxybosentan in human plasma by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The analytes and their deuterated analogs were quantitatively extracted from 100 μL human plasma by solid phase extraction. The chromatographic separation of analytes was achieved on a Thermo Hypurity C18 (100 mm × 4.6 mm, 5 μ) analytical column with a resolution factor of 2.4 under isocratic conditions. The method was validated over a dynamic concentration range of 0.4-1600 ng/mL for bosentan and 0.2-250 ng/mL for hydroxybosentan. Ion-suppression effects were investigated by post-column infusion of analytes. The precision (%CV) values for the calculated slopes of calibration curves, which would reflect the relative matrix effect, were less than 1.2% for both the analytes. The intra-batch and inter-batch precision (%CV) across quality control levels was ≤4.0% and the mean relative recovery was >94% for both the analytes. The method was successfully applied to a bioequivalence study of 125 mg tablet formulation (test and reference) in 12 healthy Indian male subjects under fasting condition. The ratios of mean log-transformed values of C(max), AUC(0-t) and AUC(0-inf) and their 90% CIs varied from 91.3 to 104.7%. The percentage change for incurred sample reanalysis (ISR) was within ±13.0%.

Effect of collision-activated dissociation gas and collision energy on the fragmentation of dipyridamole and its rapid and sensitive liquid chromatography/electrospray ionization tandem mass spectrometric determination in human plasma.

The effect of nitrogen as the collision-activated dissociation (CAD) gas on the fragmentation of dipyridamole was investigated in the range of 10-90 eV collision energy. The results support the collision model reported elsewhere, that the degree of ion fragmentation increases with the increasing mass of the collision gas. A simple, sensitive and high-throughput liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the determination of dipyridamole, a platelet aggregation inhibitor in human plasma, using granisetron as internal standard (IS). The method involved liquid-liquid extraction of the analyte and IS from 0.5 mL human plasma with diethyl ether. The chromatographic separation was achieved under isocratic conditions and the ion transitions for dipyridamole (m/z 505.40 --> 429.60) and the IS (m/z 313.10 --> 138.20) were monitored on a triple quadrupole mass spectrometer, operating in positive ion multiple reaction monitoring (MRM) mode. The method was validated over the concentration range 5.1-4499.1 ng/mL for dipyridamole. The method was rugged and rapid with a total run time of 1.2 min. It was successfully applied to a pivotal bioequivalence study in 67 healthy human subjects after oral administration of a 75 mg extended release formulation under fasting condition.