RESUMEN
BACKGROUND: Two methods have been developed and validated for the determination of free and total dopamine in human plasma. They are based on solid-phase extraction of the analyte from the matrix by covalent complexation with phenylboronic acid, followed by derivatization with ethylchloroformate. The derivative is quantified by reversed-phase liquid chromatography on a C18 column and positive electrospray ionization MS/MS. RESULTS: The high selectivity obtained, in combination with the stable and relatively non-polar nature of the derivatized analyte, enables the reliable quantification of dopamine in the range 0.05 to 20 ng/ml in a 5 min run time, using only 100 µl of sample. Total dopamine concentrations are determined (range 1 to 400 ng/ml) by including an acidic hydrolysis step, which converts the sulphate and glucuronide conjugates to free dopamine prior to extraction. The method was applied to quantify free and total dopamine levels in human plasma after dosing with the anti-Parkinson's drug combination L-dopa/carbidopa with and without entacapone. CONCLUSION: A sensitive and selective LC-MS/MS method has been developed and validated for the determination of free and total dopamine in human plasma. This article demonstrates how essential careful optimization of the sample preparation procedures was for developing a successful method.
Asunto(s)
Cromatografía Liquida/métodos , Dopamina/análisis , Dopamina/sangre , Espectrometría de Masas en Tándem/métodos , Animales , Cromatografía Liquida/instrumentación , Dopamina/química , Ésteres del Ácido Fórmico/química , Humanos , Estructura Molecular , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Extracción en Fase Sólida/métodos , Espectrometría de Masas en Tándem/instrumentaciónRESUMEN
OBJECTIVE: The purpose of this study was to investigate the pharmacokinetics of levosimendan and to determine the primary pharmacokinetic parameters of the pharmacologically active metabolite OR-1896 in rapid and slow acetylators. METHODS: Levosimendan was administered as a constant rate (0.1 microg/(kg min)) i.v. infusion for 24h in six rapid and six slow acetylators based on N-acetyltransferase 2 genotyping. At the end of the infusion, a small amount (2.5 microg/kg) of (13)C-labeled OR-1896 was administered by i.v. infusion for 10 min. Blood samples were taken at predefined sampling points 14 days post-infusion and levosimendan and its metabolite concentrations were determined by LC-MS/MS. RESULTS: Steady-state concentrations of levosimendan were achieved within 4-8h and no differences were found in the pharmacokinetics of the parent compound between the rapid and slow acetylators. The maximum concentrations of amino phenylpyridazinone metabolite OR-1855 and N-acetylated conjugate OR-1896 were observed approximately 24h after terminating the infusion. AUC of OR-1896 was approximately 3.5 times higher in the rapid acetylators compared to the slow acetylators (P = 0.002, 95% confidence interval for group ratio from 2.0 to 8.2). The mean +/- S.D. fraction of levosimendan metabolized to OR-1896 was 6.8 +/- 2.8% in the rapid and 4.3 +/- 2.4% in the slow acetylators (P = 0.12). (13)C-OR-1855 concentrations were detected in plasma after administration of (13)C-OR-1896 indicating deacetylation from OR-1896 to OR-1855. CONCLUSIONS: Plasma OR-1896 levels during and after levosimendan treatment are dependent on the acetylation status of the subject-rapid acetylators having 3.5 times higher concentrations than slow acetylators.
Asunto(s)
Acetamidas/metabolismo , Arilamina N-Acetiltransferasa/metabolismo , Cardiotónicos/farmacocinética , Hidrazonas/farmacocinética , Piridazinas/metabolismo , Piridazinas/farmacocinética , Acetilación , Adulto , Área Bajo la Curva , Arilamina N-Acetiltransferasa/genética , Proteínas Sanguíneas/metabolismo , Radioisótopos de Carbono , Genotipo , Semivida , Humanos , Hidrazonas/metabolismo , Infusiones Intravenosas , Masculino , Unión Proteica , Simendán , Factores de TiempoRESUMEN
OBJECTIVES: To study whether ageing affects the pharmacokinetics of estradiol valerate (E2V) or medroxyprogesterone acetate (MPA) in postmenopausal women. METHODS: Forty-six postmenopausal women from two essentially similar pharmacokinetic studies were divided into three age categories: under 60 years (n = 15), between 60 and 65 years (n = 18) and over 65 years (n = 13). They all were treated for 12 days or 14 days with four galenically identical tablets containing combinations of 1 mg or 2 mg E2V and 2.5 mg or 5 mg MPA. The studies followed an open, randomised cross-over design with no washout between the periods. Serum estradiol and MPA concentrations were measured at steady state on study day 12 or 14 of each period. RESULTS: No statistically significant differences were observed in the peak concentration (Cmax), time to peak (t(max)), AUC or elimination half-life for estradiol or MPA between the different age groups. In spite of the lack of statistical significance the AUC was on an average 1.6-fold and Cmax 1.40-fold higher in the oldest group of women than in the youngest group and age was found significant as a continuous variable for AUC and Cmax for MPA but not for estradiol. CONCLUSIONS: The results suggest that there would be no significant changes in the pharmacokinetics of estradiol between women under 60 and over 65 years of age. However, a significant trend towards higher MPA concentrations and bioavailability was observed with increasing age. The results suggest that from the pharmacokinetic point of view the relationship between estradiol and MPA dose to be used in elderly could be different from that in younger postmenopausal women, while no pharmacokinetic reasons to use lower estradiol doses in the elderly were observed.