Association of ABCB1, CYP3A4*18B and CYP3A5*3 genotypes with the pharmacokinetics of tacrolimus in healthy Chinese subjects: a population pharmacokinetic analysis.

WHAT IS KNOWN AND OBJECTIVE: Tacrolimus (TAC) is metabolized mainly by the CYP3A subfamily and extruded into the intestine by P-glycoprotein, which is encoded by the ABCB1 gene. Several studies have suggested that the CYP3A5*3 genotype influenced the pharmacokinetics (PK) of TAC. The CYP3A4*18B and CYP3A5*3 alleles are clinically important in Chinese subjects because of their relatively high frequency. The present study aimed at evaluating the effects of ABCB1 (C1236T-G2677T/A-C3435T), CYP3A4*18B and CYP3A5*3 genetic polymorphisms on TAC PK in healthy Chinese subjects. METHODS: Data were obtained from a comparative bioavailability study of oral TAC formulations (n = 22). TAC whole blood concentrations were measured by LC-MS/MS. Genetic polymorphisms were determined using a direct sequencing method. Nonlinear mixed-effects modelling (NONMEM) was performed to assess the effect of genotypes and demographics on TAC PKs. RESULTS AND DISCUSSION: Both CYP3A4*18B and CYP3A5*3 polymorphisms affected the TAC PK, whereas ABCB1 genetic polymorphisms and other demographic characteristics did not. The combined genotypes of CYP3A4*18B and CYP3A5*3 had a greater impact than either genotype alone, and they were estimated to account for 28·4% of the inter-subject variability of apparent clearance (CL/F) by NONMEM. The CL/F in subjects with CYP3A4*1/*1-CYP3A5*3/*3 was 10·3 L/h and was 48·5% in those not carrying CYP3A4*1/*1-CYP3A5*3/*3. WHAT IS NEW AND CONCLUSION: This is the first study to extensively explore the influence of CYP3A4*18B, CYP3A5*3 and ABCB1 genetic polymorphisms on TAC PK in healthy Chinese subjects. The results demonstrated that subjects with a combined genotype of CYP3A4*1/*1-CYP3A5*3/*3 may require lower TAC doses to achieve target concentration levels and further investigation is needed in larger populations to confirm the clinical benefits.

Reactive oxygen species in rostral ventrolateral medulla modulate cardiac sympathetic afferent reflex in rats.

AIM: The aim of the present study was to investigate whether reactive oxygen species (ROS) in rostral ventrolateral medulla (RVLM) modulate cardiac sympathetic afferent reflex (CSAR) and the enhanced CSAR response caused by microinjection of angiotensin II (Ang II) into the paraventricular nucleus (PVN). METHODS: Under urethane and alpha-chloralose anaesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in sinoaortic-denervated and cervical-vagotomized rats. The CSAR was evaluated by the RSNA response to epicardial application of capsaicin (1.0 nmol). RESULTS: Bilateral RVLM microinjection of tempol (a superoxide anion scavenger) or polyethylene glycol-superoxide dismutase (PEG-SOD, an analogue of endogenous superoxide dismutase) attenuated the CSAR, but did not cause significant change in baseline RSNA and MAP. NAD(P)H oxidase inhibitors apocynin or phenylarsine oxide (PAO) also showed similar effects, but SOD inhibitor diethyldithio-carbamic acid (DETC) enhanced the CSAR and baseline RSNA, and increased the baseline MAP. Bilateral PVN microinjection of Ang II (0.3 nmol) enhanced the CSAR and increased RSNA and MAP, which was inhibited by the pre-treatment with RVLM administration of tempol, PEG-SOD, apocynin or PAO. The pre-treatment with DETC in the RVLM only showed a tendency in potentiating the CSAR response of Ang II in the PVN, but significantly potentiated the RSNA and MAP responses of Ang II. CONCLUSION: These results suggest that the NAD(P)H oxidase-derived ROS in the RVLM modulate the CSAR. The ROS in the RVLM is necessary for the enhanced CSAR response caused by Ang II in the PVN.

HPLC determination of telmisartan in human plasma and its application to a pharmacokinetic study.

A sensitive, simple, and accurate HPLC method was developed for the assay of telmisartan in human plasma. Using naproxen as internal standard, the assay involved liquid-liquid extraction of the compound from acidified plasma into organic solvent and reversed-phase chromatography with fluorescence detection. The assay was shown to be linear from 0.5 to 1000 ng/mL. In 24 healthy volunteers, the plasma concentrations of the drug were determined after a single oral dose of 160 mg.

Population pharmacokinetic modeling of steady state clearance of carbamazepine and its epoxide metabolite from sparse routine clinical data.

OBJECTIVE: To develop a population pharmacokinetic model to evaluate the effects of variety of covariates on clearance of carbamazepine (CBZ) and its main metabolite carbamazepine-10,11-epoxide (CBZE) in Chinese population. METHODS: Serum samples at steady trough state (n = 459) were collected prospectively from 408 compliant outpatients during their routine clinical care. CBZ and CBZE concentrations were simultaneously determined by high performance liquid chromatography. Population clearance (CL) of CBZ and CBZE were estimated by non-linear mixed effect modeling and NONMEM program with a one-compartment model of first-order absorption and elimination. RESULTS: Total body weight (TBW), dose and concomitant medication were all important determinants of CL of CBZ and CBZE. The final regression model for CBZ was: where VPA = 1 for patients comedicated with valproic acid and its dose greater than 18 mg/kg, otherwise VPA = 0; PHT = 1 for patients comedicated with phenytoin, otherwise PHT = 0; PB = 1 for patients comedicated with phenytoin, otherwise PB = 0. The final regression CL model for the CBZE was: where VPA = 1 for patients comedicated with valproic acid, otherwise VPA = 0. CONCLUSION: The current models, which describe CL of CBZ and CBZE in terms of patient specific details, can be used as a reference to optimize CBZ therapy in Chinese epilepsy patients.

[Role of basolateral amygdaloid nuclei in sleep and wakeful state regulation].

The role of basolateral amygdaloid nuclei (BLN) in sleep and wakeful state (W) was investigated with polysomnography. Electrical lesion of bilateral BLN increased slow wave sleep (SWS) and paradoxical sleep (PS), but decreased W. Bilateral injection of kainic acid (KA), which selectively destroyed the soma of neurons, resulted in biphasic effects. At d 1 after KA, insomnia occurred. At d 4, SWS increased while W decreased, but PS did not change. Unilateral injection of NO donor sodium nitroferricyanide (SNP) caused an enhancement of W and a decrease of SWS. Injection of nitric oxide synthase inhibitor N-nitro-L-arginine (L-NNA) led to opposite effects. L-arginine, a precursor of NO, had no direct effect on sleep and W, but blocked the effects of L-NNA. The results suggest that BLN plays an important role in regulating sleep and wakeful state. Destruction of BLN increases SWS, and NO in BLN has W-promoting and SWS-inhibiting effects, which may be mediated by activation of neurons in BLN.

[Comparison of bioavailability between nimotop and nimodipine tablet].

A new analytical method was established for determining plasma level of nimodipine using HPLC and its application to determine the bioavailability of nimodipine. Experiments were performed on a Waters Model Baseline 810 System instrument. A 3.9 mm x 200 mm stainless steel column was packed with YWG-C18(10 microns) as the stationary phase. The mobile phase was a mixture solution of methanol--water (60/40, v/v) with 1.00 ml.min-1 at 35 degrees C. The detector was set at 358 nm. The plasma samples were extracted with ether--n-hexane (1:1). Calibration curve was linear (gamma = 0.9999) in the concentration range of 5-300 ng.ml-1. The within-day and between-day precision (RSD) were less than 3% and 5%, respectively, with average recoveries of 97.67%-102.3%. The study on bioavailability of numodipine between tablet A (made in China) and nimotop (Bayer, Germany) was carried out in 8 volunteers at the oral dose of 120 mg by cross-over method. Two-compartment open model was suitable for describing the disposition of nimodipine. The main pharmacokinetic parameters were shown in Tab 1 and mean plasma concentration--time curve of nimodipine was shown in Fig 1. The results indicate that tablet A exhibited a lower bioavailability (relative to nimotop). We suggest that the product tablet A must be improved in formula and technology.