The development and validation of quantitative methods for the determination of stavudine and alfuzosin in plasma and monic acid in urine

English: The development and validation of bio-analytica) assay methods suitable for the quantification of stavudine in plasma, alfuzosin in plasma and monic acid in urine is discussed. A short summary of these methods are given: • A sensitive method for the determination of stavudine in plasma was developed, using highperformance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted from plasma with Waters, Sep-Pak®Vac, 100 mg, tC18®solid phase extraction (SPE) columns. Chromatography was performed on a Supelco Discovery" C18, 5 urn, 150 x 2 mm column with a mobile phase consisting of ammonium acetate (0.01 M): acetonitrile: methanol (800:100:100, v/v/v) at a flow rate of 0.3 ml/min. Detection was achieved by an Applied Biosystems API 2000 mass spectrometer (LC-MS/MS) set at unit resolution in the multiple reaction monitoring mode (MRM). Atmospheric pressure chemical ionization (APCl) was used to obtain deprotonated ions (molecular ion m/z 223.1 to the product ion m/z 42.01). The mean recovery for stavudine was 94 % with a lower limit of quantification set at 4 ng/ml. This assay method makes use of the increased sensitivity and selectivity of mass spectrometric (MS/MS) detection to allow for a more rapid (extraction and chromatography) and selective method for the determination of stavudine in human plasma than has previously been published. The assay metod was used to quantitatively determine stavudine concentrations in plasma samples to follow the concentration vs. time profile for at least five half lives of the drug after a single 40 mg oral dose of stavudine was given to healthy adult male human subjects. • A selective, sensitive and rapid liquid chromatography-tandem mass speetrometry method for the determination of alfuzosin in plasma was developed. An Applied Biosystems API 2000 triple quadrupole mass speetrometer in multiple reaction monitoring (MRM) mode, using TurboIonSpray (TIS) with positive ionisation was used (molecular ion of alfuzosin m/z 390.2 to the product ion m/z 71.2; molecular ion of prazosin m/z 384.2 to the product ion m/z 95.0). Using prazosin as an internal standard, liquid-liquid extraction was followed by CI8 reversed phase liquid chromatography and tandem mass spectrometry. The mean recovery for alfuzosin was 82.9 % with a lower limit of quantification set at 0.298 ng/ml, the calibration range being between 0.298 and 38.1 ng/ml. This assay method makes use of the increased sensitivity and selectivity of tandem mass spectrometric (MS/MS) detection to allow for a more rapid (extraction and chromatography) and selective method for the determination of alfuzosin in human plasma than has previously been published. The assay method was used to quantify alfuzosin in human plasma samples generated in a multiple-dose (5 mg bd.) study at steady state. • Two selective methods for the determination of monic acid (a metabolite of mupirocin) in urine were developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. An Applied Biosystems API 2000 triple quadrupole mass spetrometer in multiple reaction monitoring (MRM) mode, using TurboIonSpray (TIS) with positive ionisation, was used (molecular ion of monic acid m/z 345.2 to the product ion m/z 327.0) The minimal sample preparation and short chromatography time (retention time ~ 3.8 min.) makes these methods suitable for the assay of large numbers of samples per day. Linearity (weighted 1/concentratiorr²) was established from 50.1 to 1001 ng/ml for the direct injection method, and linearity (weighted 1/concentration) was established from 15.8 to 1013 ng/ml for the SPE method. The assay method was used for the determination of monic acid concentrations in human urine in order to detect and quantify the absorption of mupirocin after multiple topical applications ofO.5 g of a 2 % ointment. Analytical data that were generated during these three research projects are discussed in this dissertation, improvements and novelties to existing methods are elucidated. The methods for the determination of stavudine and alfuzosin have been published. Both full-length publications are included in this dissertation, together with correspondence between myself and the journal editors and referees. The assay methods for monic acid will soon be submitted for publication in the Journal of Chromatography B.