DETERMINATION OF NANOGRAM LEVELS OF PEPTIDE DRUG IN RABBIT AND HUMAN PLASMA USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY COUPLED WITH ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

High-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) using an electrospray ionization (ESI) interface provides a sensitive method for the quantitative analysis of peptide drugs in complex biological matrixes. ESI HPLC-MS was applied to the analysis of a pentapeptide drug (IRI-514) in rabbit and human plasma. Prior to analysis, the plasma samples were prepared using protein precipitation followed by solid-phase extraction. The lower limit of quantitation using selected ion monitoring was determined to be 2 ng/mL, when 8 mL of human plasma spiked with 1-40 ng/mL was extracted. Rabbit plasma (1 mL) samples spiked with 10-40 000 ng of authentic drug/mL gave a linear response when a deuterated peptide analog was employed as an internal standard. A commercial ESI interface was modified to permit higher flow rates (10-20 mu L/min) to enter the mass spectrometer source. The revised interface provided a 10-fold increase in sensitivities and permitted the use of standard HPLC columns (2.0-mm i.d.) and HPLC instrumentation. ESI HPLC-MS analysis was automated to provide unattended, precise, and sensitive detection of small peptides in both human and rabbit plasma. Using this methodology, a toxicokinetic study of intravenously administered IRI-514 at three dose levels indicated that the area under the curve values were dose proportional.