Development and Validation of UPLC-MS/MS Method for Quantifying of Free and Total Dabigatran in Human Plasma: An Application for a Bioequivalence Study

Dabigatran etexilate mesylate (DABE), a prodrug, quickly changes in our bodies after its oral administration into dabigatran (DAB). Accordingly, detecting DABE in plasma is practically unmanageable. A UPLC-MS/MS technique was developed and validated to compute free DAB in participants. For the first time, the central composite design- a type of response surface methodology- was utilized for optimizing variables affecting the cleavage of glucuronide bond. Additionally, the pharmacokinetic parameters of generic medication (okanadab) were determined, and the obtained outcomes were compared to those of branded drug (pradaxa®). The sample preparation was done using methanol as a protein precipitant and the separation was achieved via ACQUITY UPLC BEH C18 column (2.1x50mm, 1.7μm). The elution was isocratically conducted using 10mM ammonium formate: methanol (72:28, v/v) as a mobile phase (MP) and the flow rate was 0.25mL/min. Multiple reaction monitoring (MRM) and positive electrospray ionization (ESI) were used. The determination was performed within 1min, and the calibration growth curve was established over a range of (1.19 - 475) ng/mL using dabigatran-d3 as a tagged internal standard (IS). Bioequivalence research was validated following FDA guidelines for bio-analytical procedures and acceptable outcomes were achieved. The outcomes for okanadab and pradaxa® did not differ significantly.

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.

Quantification of dabigatran and indirect quantification of dabigatran acylglucuronides in human plasma by LC-MS/MS

BACKGROUND

An assay for the quantification of dabigatran and its active metabolites, dabigatran acylglucuronides, has not previously been described in detail.

RESULTS

For the quantification of total dabigatran concentration (free dabigatran and acylglucuronides), samples were subjected to alkaline hydrolysis. For the quantification of free dabigatran, samples were acidified with ammonium formate. Following acetonitrile protein precipitation, the samples were analyzed by LC-MS/MS using gradient elution to ensure separation of dabigatran from dabigatran acylglucuronides. Mean recoveries ≥98% were achieved. The assay was validated over the range 2.5-1000 ng/ml dabigatran, imprecision was <9% CV (<15% at LLOQ) and accuracy was 101-114%.

CONCLUSION

An assay for dabigatran with indirect quantification of dabigatran acylglucuronides in plasma was developed, validated and applied.

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.

Practical approaches to incurred sample LC-MS/MS reanalysis: confirming unexpected results

Incurred sample reanalysis (ISR) is an important step in assuring the quality of an LC-MS/MS bioanalytical assay and the integrity of bioanalysis conduct. A conventional ISR involves analysis of at least 20 samples taken from an in vivo study a second time using the method that was described in prestudy validation and employed in generating the initial study sample results. However, this practice is sometimes inadequate to confirm bioanalytical results that are unexpected. The present report discusses several additional exploratory activities that were performed to confirm the unexpected plasma concentration-time results of NVP-1, an investigational drug candidate, observed in the plasma samples collected from patients in a phase II trial. These approaches include (1) LC-MS/MS reanalysis of the study samples after multiple freeze/thaw cycles followed by a short-term benchtop storage, (2) evaluation of additional MS/MS transitions in LC-MS/MS, (3) employment of a different sample preparation procedure in LC-MS/MS, and (4) study sample dilution using plasma samples from healthy volunteers. These procedures are practical and can be readily implemented in the confirmatory LC-MS/MS bioanalysis of other small molecules.

Potentially new isobaric metabolite of fluvastatin observed by LC–MS/MS during incurred sample analysis

Background: Fluvastatin (Lescol®) is a racemic mixture of two erythro stereoisomers and metabolizes into two threo stereoisomers. A method was developed to chromatographically separate fluvastatin from its threo isomers to support a bioequivalence study. Results: During incurred samples analysis, an additional peak sharing the same mass transition as fluvastatin was observed and interfered with fluvastatin’s quantification. Consequently, the chromatographic conditions were modified in order to resolve fluvastatin and the interference. Extensive evaluations were performed to ensure that the interference is not a degradation product generated during sample processing. Conclusion: An isobaric compound of fluvastatin was discovered, which required chromatographic separation from fluvastatin to obtain a reliable bioanalytical method. The investigation performed suggests that the interference is produced in vivo and is a possible metabolite of fluvastatin.