title: Nonlinear calibrations on the assay of dilitiazem and two of its metabolites from plasma samples by means of liquid chromatography and ESI/MS(2) detection: application to a bioequivalence study.
abstract: The assay of diltiazem (DLTZ) and its active metabolites desacetyldiltiazem (DAcD) and desmethyldiltiazem (DMeD) in plasma samples was achieved by means of an HPLC/(ESI)MS(2) method. The diastereoisomer of diltiazem, namely {(2R,3S)-5-[2-(dimethylamino)ethyl]-2-(4-methoxyphenyl)-4-oxo-2,3,4,5-tetrahydro-1,5-benzothiazepin-3-yl acetate} was used as internal standard (IS). Sample preparation was based on protein precipitation by means of organic solvent addition (acetonitrile). The isocratic elution based on a reversed-phase mechanism allows good separation of the analytes within 15 min. Atmospheric pressure electrospray ionization was used. All analytes were monitored in the MS(2)-MRM mode. A fragmentation schema is proposed for the target compounds. As the method was designed for bioequivalence purposes, a full validation procedure was considered. On validation, nonlinear calibrations were observed. Consequently, concentration intervals requiring nonlinear calibrations are discussed. Low limits of quantification in the 0.6-1 ng/mL concentration range were obtained. The analytical method was successfully applied to a single dose (120 mg), open-label, randomized, two-period, two-sequence, crossover bioequivalence study of two commercially available solid oral dosage pharmaceutical formulations (tablets).
authors.affiliation: S.C. Labormed Pharma S.A., Splaiul Independentei no. 319 E, Bucharest 060044, Romania.
authors.forename: Cristina
authors.initials: C
authors.lastname: Georgita
authors.forename: Florin
authors.initials: F
authors.lastname: Albu
authors.forename: Victor
authors.initials: V
authors.lastname: David
authors.forename: Andrei
authors.initials: A
authors.lastname: Medvedovici
mesh_terms: D000328:Adult; D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D018592:Cross-Over Studies; D004110:Diltiazem / Q000097:blood* / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013810:Therapeutic Equivalency
chemical_list: D004110:Diltiazem