RESUMEN
PURPOSE: To characterize the pharmacokinetics of cetirizine enantiomers in the guinea pig including protein binding in both the guinea pig and human plasma. METHODS: Plasma concentrations of cetirizine enantiomers in the guinea pig were determined using a LC-MS/MS method after a short i.v. infusion (1, 2 and 4 mg/kg) of racemic cetirizine. Protein binding was determined using an in vitro equilibrium dialysis technique. A pharmacokinetic model was developed using NONMEM and the differences in pharmacokinetic parameters of levocetirizine and dextrocetirizine were estimated. RESULTS: The plasma concentration time data of both the enantiomers were best described by a three-compartment pharmacokinetics model. The clearance (CL) of levocetirizine and dextrocetirizine was 1.2 and 2.7 ml/min, respectively, and the volume of distribution at steady state (Vss) was 457 ml and 996 ml, respectively. The fraction unbound (fu) in guinea pig plasma for levocetirizine and dextrocetirizine was 7-10% and 16-21% while in human plasma, it was 8% and 12%, respectively. The factor describing the difference in the pharmacokinetic parameters of the cetirizine enantiomers was estimated to be 2.26. CONCLUSIONS: Cetirizine pharmacokinetics is stereoselective in the guinea pig. For levocetirizine, fu, CL and Vss were half those of dextrocetirizine, indicating that protein binding is an important factor affecting the pharmacokinetics of cetirizine. The effect of protein binding on the pharmacokinetics of the cetirizine enantiomers could be extrapolated to humans.
Asunto(s)
Antialérgicos/química , Antialérgicos/farmacocinética , Cetirizina/química , Cetirizina/farmacocinética , Animales , Diálisis , Cobayas , Humanos , Modelos Estadísticos , Unión Proteica , EstereoisomerismoRESUMEN
The objective of this study was to compare the blood-brain barrier (BBB) transport and brain distribution of levo- (R-CZE) and dextrocetirizine (S-CZE). Microdialysis probes, calibrated using retrodialysis by drug, were placed into the frontal cortex and right jugular vein of eight guinea pigs. Racemic CZE (2.7 mg/kg) was administered as a 60-min i.v. infusion. Unbound and total concentrations of the enantiomers were measured in blood and brain with liquid chromatography-tandem mass spectrometry. The brain distribution of the CZE enantiomers were compared using the parameters K(p,) K(p,u,) K(p,uu), and V(u,br). K(p) compares total brain concentration to total plasma concentration, K(p,u) compensates for binding in plasma, whereas K(p,uu) also compensates for binding within the brain tissue and directly quantifies the transport across the BBB. V(u,br) describes binding within the brain. The stereoselective brain distribution indicated by the K(p) of 0.22 and 0.04 for S- and R-CZE, respectively, was caused by different binding to plasma proteins. The transport of the CZE enantiomers across the BBB was not stereoselective, since the K(p,uu) was 0.17 and 0.14 (N.S.) for S- and R-CZE, respectively. The K(p,uu) values show that the enantiomers are effluxed to a large extent across the BBB. The V(u,br) of approximately 2.5 ml/g brain was also similar for both the enantiomers, and the value indicates high binding to brain tissue. Thus, when determining stereoselectivity in brain distribution, it is important to study all factors governing this distribution, binding in blood and brain, and the BBB equilibrium.
Asunto(s)
Antialérgicos/farmacocinética , Barrera Hematoencefálica/metabolismo , Encéfalo/metabolismo , Cetirizina/farmacocinética , Antagonistas de los Receptores Histamínicos H1 no Sedantes/farmacocinética , Animales , Antialérgicos/sangre , Proteínas Sanguíneas/metabolismo , Cetirizina/sangre , Líquido Extracelular/química , Cobayas , Antagonistas de los Receptores Histamínicos H1 no Sedantes/sangre , Masculino , Microdiálisis , EstereoisomerismoRESUMEN
The synthesis and biological evaluation of a novel family of M(3) muscarinic antagonists are described. A systematic modification of the substituents to a novel alkyne-quinuclidine scaffold yielded original compounds displaying potent in vitro anticholinergic properties.
Asunto(s)
Antagonistas Muscarínicos/farmacología , Quinuclidinas/farmacología , Receptores Muscarínicos/efectos de los fármacos , Animales , Sitios de Unión , Inhibidores del Citocromo P-450 CYP2D6 , Citocromo P-450 CYP3A , Inhibidores Enzimáticos del Citocromo P-450 , Evaluación Preclínica de Medicamentos , Cobayas , Humanos , Técnicas In Vitro , Microsomas/efectos de los fármacos , Microsomas/enzimología , Estructura Molecular , Antagonistas Muscarínicos/síntesis química , Antagonistas Muscarínicos/química , Quinuclidinas/síntesis química , Quinuclidinas/química , Receptores Muscarínicos/metabolismo , Relación Estructura-ActividadRESUMEN
Sensitive enantioselective liquid chromatographic assays using tandem mass spectrometric detection were developed and validated for the determination of S-cetirizine (S-CZE) and R-cetirizine (R-CZE) in guinea pig plasma, brain tissue, and microdialysis samples. Enantioselective separation was achieved on an alpha1-acid glycoprotein column within 14 min for all methods. A cetirizine analog, ucb 20028, was used as internal standard. Cetirizine and the internal standard were detected by multiple reaction monitoring using transitions m/z 389.1 --> 200.9 and 396.1 --> 276.1, respectively. The samples were prepared using protein precipitation with acetonitrile. For guinea pig plasma, the assay was linear over the range 0.25-5000 ng/mL for both S-CZE and R-CZE, with a lower limit of quantification (LLOQ) of 0.25 ng/mL. For the brain tissue and microdialysis samples, the assays were linear over the range 2.5-250 ng/g and 0.25-50 ng/mL, respectively, and the LLOQ values were 2.5 ng/g and 0.25 ng/mL, respectively. The intra- and inter-day precision values were < or =7.1% and < or =12.6%, respectively, and the intra- and inter-day accuracy varied by less than +/-8.0% and +/-6.0% of the nominal value, respectively, for both enantiomers in all the matrices investigated.
Asunto(s)
Encéfalo/metabolismo , Cetirizina/análogos & derivados , Cetirizina/sangre , Cromatografía Líquida de Alta Presión , Antagonistas de los Receptores Histamínicos H1 no Sedantes/sangre , Espectrometría de Masa por Ionización de Electrospray/métodos , Animales , Química Encefálica , Cetirizina/farmacocinética , Cobayas , Antagonistas de los Receptores Histamínicos H1 no Sedantes/farmacocinética , Microdiálisis , Reproducibilidad de los Resultados , EstereoisomerismoRESUMEN
Levetiracetam (2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA, a novel antiepileptic drug, has been shown to bind to a specific binding site located in brain (levetiracetam binding site [Eur. J. Pharmacol. 286 (1995) 137]). However, [3H]levetiracetam displayed only micromolar affinity for these sites making it an unsuitable probe for further characterization. The present study describes the binding properties of an analogue of levetiracetam: [3H]ucb 30889, (2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide. [3H]ucb 30889 binds reversibly to specific binding sites in rat brain. Kinetics at 4 degrees C were biphasic with half-times of association and dissociation of, respectively, 3 and 4 min for the fast component and 47 and 61 min for the slow component. [3H]ucb 30889 saturation binding curves were compatible with the labelling of a homogenous population of binding sites having a B(max) of 4496+/-790 fmol/mg protein (mean+/-S.D., n=5) and a K(d) of 62+/-20 nM (mean+/-S.D., n=5), a 20-fold increase in affinity compared to [3H]levetiracetam. Competition binding curves with ligands known to interact with levetiracetam binding sites and tissue distribution restricted to the brain indicated that [3H]ucb 30889 and [3H]levetiracetam bind to the same site. Although levetiracetam binding sites and GABA(A) (gamma-aminobutyric acid) receptors share some ligands such as pentobarbital and pentylenetetrazol, experiments performed with [35S]TBPS (tert-butyl-bicyclo[2.2.2]phosporothionate), a probe for the GABA(A) Cl(-) channel do not support the hypothesis that levetiracetam binding sites are part of the GABA(A) receptor complex. Preliminary autoradiography studies in rat brain revealed that [3H]ucb 30889 labels specific sites in all brain regions and that this binding is concentration-dependently displaced by levetiracetam.
Asunto(s)
Anticonvulsivantes/metabolismo , Azidas/metabolismo , Encéfalo/metabolismo , Piracetam/metabolismo , Pirrolidinas/metabolismo , Animales , Anticonvulsivantes/química , Azidas/química , Unión Competitiva/efectos de los fármacos , Unión Competitiva/fisiología , Encéfalo/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Levetiracetam , Masculino , Piracetam/análogos & derivados , Piracetam/química , Pirrolidinas/química , Ratas , Ratas Sprague-Dawley , Distribución Tisular/efectos de los fármacos , Distribución Tisular/fisiología , Tritio , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
We characterised histamine H(1) receptor antagonism by cetirizine and its enantiomers on isolated guinea pig ileum and trachea. Competitive or mixed (competitive and apparent noncompetitive) antagonism profiles were observed. The order of potency was: chlorpheniramine> or =mepyramine>levocetirizine>cetirizine> or =terfenadine>loratadine>dextrocetirizine. The inhibitory effects of cetirizine, levocetirizine, terfenadine and loratadine were slowly reversible compared to those of dextrocetirizine or mepyramine. Cetirizine and its enantiomers were inactive on L-type Ca(2+) channels. Reduction of the histamine H(1) receptor reserve by dibenamine in the ileum (100-fold higher than in the trachea) showed a gradual change from the competitive profile of dextrocetirizine and mepyramine to a mixed profile. The present results show that cetirizine and levocetirizine are selective competitive but slowly reversible histamine H(1) receptor antagonists. Their mixed antagonism profile observed in the trachea can be explained by the small receptor reserve present in this tissue compared to the ileum and their very slow dissociation rate from the histamine H(1) receptor.
Asunto(s)
Cetirizina/farmacología , Antagonistas de los Receptores Histamínicos H1/farmacología , Íleon/efectos de los fármacos , Receptores Histamínicos H1/metabolismo , Tráquea/efectos de los fármacos , Animales , Aorta/efectos de los fármacos , Aorta/metabolismo , Relación Dosis-Respuesta a Droga , Cobayas , Histamina/metabolismo , Histamina/farmacología , Antagonistas de los Receptores Histamínicos H1/metabolismo , Íleon/metabolismo , Técnicas In Vitro , Masculino , Ratas , Tráquea/metabolismoRESUMEN
Competition experiments with [(3)H]mepyramine showed that cetirizine and its enantiomers, levocetirizine and (S)-cetirizine, bound with high affinity and stereoselectivity to human H(1) histamine receptors (K(i) values of 6, 3, and 100 nM, respectively). Cetirizine and levocetirizine were 600-fold more selective for H(1) receptors compared with a panel of receptors and channels. Binding results indicated that the interaction between cetirizine, its enantiomers, and histamine is compatible with a competitive behavior, in contrast with the noncompetitive profile of cetirizine and levocetirizine observed in isolated organs. Binding kinetics provided a suitable explanation for this observation, because levocetirizine dissociated from H(1) receptors with a half-time of 142 min; that of (S)-cetirizine was only 6 min, implying that the former could act as a pseudo-irreversible antagonist in functional studies. The carboxylic function of levocetirizine seemed responsible for its long dissociation time. Indeed, hydroxyl or methyl ester analogs dissociated more rapidly from H(1) receptors, with half-times of 31 min and 7 min, respectively. The importance of the carboxylic function of levocetirizine for the interaction with the H(1) receptor was further supported by the results from the mutation of Lys(191) to Ala(191). This mutation decreased the dissociation half-time of levocetirizine from 142 to 13 min and reduced its affinity from 3 to 12 nM, whereas the affinity and dissociation kinetics of hydroxyl and methyl ester analogs were hardly affected. The mutation of Thr(194) reduced the binding stereoselectivity by selectively enhancing the affinity of the distomer.