Determination of eptifibatide concentration in human plasma utilizing the liquid chromatography–tandem mass spectrometry method

Validated High Performance Liquid Chromatographic Method for Stability Study of Eptifibatide

Eptifibatide (EPT) is a cyclic heptapeptide derived from a protein found in the venom of the south-eastern pygmy rattle snake used as an antiplatelet drug. In this study, a newly developed HPLC method demonstrating no interference from the different degradation products of EPT has been optimized and validated. The method was based on HPLC separation of eptifibatide from its degradation products using reversed phase C18 column at ambient temperature with mobile phase consisting of acetonitrile: 50 mM sodium dihydrogen orthophosphate dihydrate, pH was adjusted to 2.2 with orthophosphoric acid (25:75 v/v). Quantitation was achieved with UV detection at 220 nm based on peak area. The proposed method was validated according to the ICH guidelines and applied to evaluate the stability of EPT under different stress conditions including temperature, oxidation and hydrolysis over wide pH range (2-10). Moreover, kinetic study of EPT oxidation and its hydrolysis at pH 10 was demonstrated. The proposed method was successfully applied to quantify EPT in bulk powder and in pharmaceutical formulation with a runtime shorter than all the reported methods.

Spectrofluorimetric determination of eptifibatide in human plasma and dosage form

A spectrofluorimetric method for the determination of eptifibatide is presented based on its native fluorescence. The type of solvent and the wavelength of maximum excitation and emission were carefully selected to optimize the experimental conditions. Under the specified experimental conditions, the linearities obtained between the emission intensity and the corresponding concentrations of eptifibatide were in the range 0.1-2.5 μg/ml for the calibration curve constructed for direct determination of eptifibatide in dosage form and 0.05-2.2 μg/ml for the calibration curve constructed in spiked human plasma with a good correlation coefficient (r > 0.99). The lower limit of quantification for the calibration curve constructed in human plasma was 0.05 μg/ml. Recovery results for eptifibatide in spiked plasma samples and in dosage form, represented as mean ± % RSD, were 95.17 ± 1.94 and 100.29 ± 1.33 respectively. The suggested procedures were validated according to the International Conference on Harmonization (ICH) guidelines for the direct determination of eptifibatide in its pure form and dosage form and United States Food and Drug Administration (US FDA) Guidance for Industry, Bioanalytical Method Validation for the assay of eptifibatide in human plasma.

Studying disulfide bond rearrangement by MALDI-RTOF PSD and MALDI-TOF/RTOF high-energy CID (20 keV) experiments of peptides derived from ammodytoxins

Ammodytoxins (Atxs) are presynaptically neurotoxic phospholipases present in Vipera ammodytes ammodytes snake venom. Atxs show a high sequence homology and contain 14 cysteines which form seven biologically relevant disulfide bridges-connecting non-neighboring cysteines. Formic acid cleavage was performed to confirm protein sequences by MALDI RTOF MS and resulted in 95.6% sequence coverage exhibiting only few formylations. Cysteine-containing peptides showed adjacent signals 2 and/or 4 Da lower (according to the number of cysteines present in the peptide) than the theoretical molecular weight indicating disulfide bridge rearrangement. Post-source decay (PSD) and high-energy collision-induced dissociation (CID) at 20 keV experiments showed fragmentation pattern unique for the reduced, thiol group containing and the oxidized, disulfide bridge harboring peptides. Besides typical low-energy fragment ions observed during PSD experiments (a-, b-, y-type ions), additional high-energy fragment ions (c-, x-, w-, d-type and internal fragments) of significant intensity were generated during fragmentation at 20 keV. In the case of charge directing N- and C-termini, x- and w-type ions were also observed during PSD. Good and up to complete sequence coverage was achieved for all studied peptides from Atxs in the case of high-energy CID, whereas PSD lacked information particularly for larger peptides.