Physicochemical and biological evaluation of P792, a rapid-clearance blood-pool agent for magnetic resonance imaging

RATIONALE AND OBJECTIVES: To summarize the physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P792, a new monogadolinated MRI blood-pool agent. METHODS: The molecular modeling of P792 was described. The r1 relaxivity properties of P792 were measured in water and 4% human serum albumin at different magnetic fields (20, 40, 60 MHz). The stability of the gadolinium complex was assessed. The pharmacokinetic and biodistribution profiles were studied in rabbits. Renal tolerance in dehydrated rats undergoing selective intrarenal injection was evaluated. Hemodynamic safety in rats and in vitro histamine and leukotriene B4 release were also tested. RESULTS: The mean diameter of P792 is 50.5 A and the r1 relaxivity of this monogadolinium contrast agent is 29 L x mmol(-1) x s(-1) at 60 MHz. The stability of the gadolinium complex in transmetallation is excellent. The pharmacokinetic and biodistribution profiles are consistent with that of a rapid-clearance blood-pool agent: P792 is mainly excreted by glomerular filtration, and its diffusion across normal endothelium is limited. Renal and hemodynamic safety is comparable to that of the nonspecific agent gadolinium-tetraazacyclododecane tetraacetic acid. No histamine or leukotriene B4 release was found in RBL-2H3 isolated mastocytes. CONCLUSIONS: The relaxivity of P792 at clinical field is very high for a monogadolinium complex without protein binding. The pharmacokinetic and biodistribution profiles are consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Experimental and clinical studies are underway to confirm the potential of P792 in MRI.     

New techniques in MR imaging of brain tumors

The past decade has seen many new MR imaging techniques that have been applied to brain tumor imaging. As MR imaging is applied further to cellular and molecular imaging (e.g., imaging of gene transfer and expression), more possibilities for brain tumor diagnosis and treatment will become evident. The superior contrast, resolution, and lack of need for image coregistration suggest that MR imaging techniques may displace PET as the preeminent modality for studying brain and tumor physiology and chemistry for indications other than receptor-based imaging. Nevertheless, the new MR imaging techniques require further histologic, physiologic, and intraoperative validation in suitable animal models and in clinical studies, and should be used to complement PET. Application of echo-planar imaging and other fast imaging sequences can permit the merger of several MR imaging studies (e.g., perfusion imaging, DWI, and MRS(I) into a typical (1-hour) clinical time slot). Synergistic information provided by these new techniques might soon enable physicians to reach the ultimate goals of noninvasive tumor grading and avoidance of having to obtain a biopsy.     

Deactivation of the sympathetic nervous system in patients with chronic congestive heart failure

In this article, we review the basic biology, signal transduction pathways, and clinical pharmacology associated with cardiac β-adrenergic receptors (β-ARs) in the context of the use of β-blocking agents in patients with chronic congestive heart failure. Adrenergic receptors, particularly the β-AR subtypes (β₁-AR and β₂-AR), are known to play a critical role in the modulation of cardiac function, providing for both "adaptive" and "maladaptive" compensatory changes. In the context of exercise or self-preservation, the adrenergic nervous system, acting via β-ARs permits an appropriately rapid, highly-dynamic increase in cardiac function. Conversely, in individuals with chronic congestive heart failure, the sustained, heightened activation of adrenergic nervous system, as manifested by increases in circulating catecholamines, results in downregulation and desensitization of myocardial β-ARs, and potentially, significant myocardial damage. A number of recent clinical trials have demonstrated a marked mortality benefit from using β-blocking agents such as metoprolol and carvedilol in patients with heart failure. The pharmacologic properties of several of these drugs and some of the specifics of their usefulness and limitations are discussed herein.     

The effect of ketanserin, a specific serotonin antagonist, on burn shock hemodynamic parameters in a porcine burn model

A number of vasoactive substances, including serotonin, have been implicated in the pathophysiology of burn shock. Ketanserin, a specific serotonin antagonist, was investigated in a porcine burn shock model. Fifteen swine were given a mean 44% total body surface area full-thickness scald burn and received fluid resuscitation with Ringer's lactate for 24 hours postburn. The swine were divided into three groups: Group I (control group) received no ketanserin; Group II received ketanserin as a single intramuscular dose preburn and continuously via intravenous drip postburn; and Group III received ketanserin continuously via intravenous drip postburn only. The ketanserin-treated groups demonstrated improved cardiac index, decreased pulmonary artery pressures, and smaller arteriovenous oxygen content differences compared to the control group in the early postburn period. Ketanserin should be investigated further as a possible adjunctive therapeutic agent during burn shock resuscitation.     

The role of dialysate in the stimulation of interleukin-1 production during clinical hemodialysis

To evaluate the role of the dialysate in the stimulation of interleukin-1 (IL-1) production during clinical hemodialysis (HD), we studied maintenance HD patients in two experiments. Cellulosic hollow-fiber dialyzers were obtained after 20 minutes of HD using either nonsterile standard dialysate (n = 6) or sterile pyrogen free 0.9% saline as dialysate (n = 6). After rinsing the blood compartment with normal saline, dialyzers were incubated at 37 degrees C for six hours. Aliquots from the blood compartment were analyzed for the presence of IL-1 by (1) rabbit pyrogenic response after intravenous injection or (2) thymocyte co-proliferation assay. The in vivo assay showed a significantly greater febrile response when standard dialysate was used than in the sterile saline group (P less than .001), and this response could be abolished by heat inactivation of aliquots (P less than .001). The in vitro assay confirmed the presence of significantly greater amounts of IL-1 (P less than .05). Studies were repeated using filter sterilized standard dialysate (n = 6) v standard dialysate (n = 6) for 240 minutes of clinical HD. The in vitro assay revealed significantly lower IL-1 levels in the filtered sterilized dialysate group (P less than .05), however, a blank control assay showed yet significantly lower levels (P less than .05). We conclude that IL-1 is produced during clinical HD and that endotoxin or its fragments play a role in the stimulation of IL-1 production, probably through monocytes adhering to the dialysis membrane. In addition to this dialysate factor, IL-1 production appears also to be stimulated by a blood-membrane interaction.     

Synthesis of new benzoxazinone derivatives as neuropeptide Y5 antagonists for the treatment of obesity

Screening of our internal chemical collection against the neuropeptide Y5 (NPY Y5) receptor allowed the identification of a benzoxazine derivative 5f as a hit that showed moderate affinity (IC(50) = 300 nM). With the aim of improving the in vitro potency, a series of 2-benzoxazinone derivatives have been synthesized and tested for NPY Y5 activity. Most of the compounds were found to be potent and selective NPY Y5 antagonists having nanomolar binding affinities for the NPY Y5 receptor and showing functional antagonism in the forskolin-induced cyclic AMP test. Prelimminary studies in order to understand the structure-activity relationship were undertaken. Selected compounds were further evaluated for in vivo efficacy, affording the lead compound 2-[4-(8-methyl-2-oxo-4H-benzo[d][1,3]oxazin-1-yl)piperidin-1-yl]-N-(9-oxo-9H-fluoren-3-yl)acetamide 5p, which displayed in vivo activity reducing food intake in rodents.     

Recombinant human erythropoietin for the treatment of renal anaemia in children: no justification for bodyweight-adjusted dosage

BACKGROUND: Drug doses for children are usually calculated by reducing adult doses in proportion to bodyweight. The clinically effective dose of recombinant human erythropoietin (epoetin) in children, however, seems to be higher than predicted by this calculation. OBJECTIVE: To determine the quantitative relationship between epoetin dose, bodyweight and response in children with end-stage renal disease. PATIENTS AND METHODS: The time-course of haemoglobin in 52 children during long-term treatment with epoetin beta was analysed by population pharmacodynamic modelling. Patients were 5-20 years old and weighed 16-53kg at the beginning of treatment. Epoetin beta was given intravenously three times per week after haemodialysis. Doses ranged from 110 to 7500IU (3-205 IU/kg). Haemoglobin versus time was described by assuming that the haemoglobin level rises after each dose due to the formation of new red blood cells, which then survive according to a logistic function. The initial rise after each dose was modelled in terms of absolute dose (not dose/kg). A parametric analysis was done with NONMEM, followed by a nonparametric analysis with NPAG. RESULTS: Dose-response was best described by a sigmoid maximum-effect (E(max)) model with median E(max) = 0.29 g/dL, median 50% effective dose (ED(50)) = 2400IU and shape parameter gamma = 2. The estimated median survival time of the epoetin-induced red blood cells, tau, was 76 days. Neither of the dose-response parameters E(max) and ED(50) showed dependence on bodyweight. The median haemoglobin response to a standard dose, 0.042 g/dL for 1000IU, was similar to that reported for adults with intravenous administration. CONCLUSIONS: Doses for children in this age range should be specified as absolute amounts rather than amounts per unit bodyweight. Initial doses can be calculated individually, based on haemoglobin level before treatment, the desired haemoglobin at steady state and the median population parameters E(max), ED(50) and tau.     

13年室间质控菌株鉴定工作的实践和体会

为了提高菌株鉴定水平, 我们自1985～1998 年参加了省临检中心细菌室间质控工作, 共鉴定下发菌株142 株,鉴定正确131 株(占92.25% ), 误检11 株(7.75% )。本文总结了鉴定工作的经验, 并对误检原因进行分析。认为理论、实践和学科新进展是提高鉴定水平的关键     

Parametric and nonparametric population methods: their comparative performance in analysing a clinical dataset and two Monte Carlo simulation studies

BACKGROUND AND OBJECTIVES: This study examined parametric and nonparametric population modelling methods in three different analyses. The first analysis was of a real, although small, clinical dataset from 17 patients receiving intramuscular amikacin. The second analysis was of a Monte Carlo simulation study in which the populations ranged from 25 to 800 subjects, the model parameter distributions were Gaussian and all the simulated parameter values of the subjects were exactly known prior to the analysis. The third analysis was again of a Monte Carlo study in which the exactly known population sample consisted of a unimodal Gaussian distribution for the apparent volume of distribution (V(d)), but a bimodal distribution for the elimination rate constant (k(e)), simulating rapid and slow eliminators of a drug. METHODS: For the clinical dataset, the parametric iterative two-stage Bayesian (IT2B) approach, with the first-order conditional estimation (FOCE) approximation calculation of the conditional likelihoods, was used together with the nonparametric expectation-maximisation (NPEM) and nonparametric adaptive grid (NPAG) approaches, both of which use exact computations of the likelihood. For the first Monte Carlo simulation study, these programs were also used. A one-compartment model with unimodal Gaussian parameters V(d) and k(e) was employed, with a simulated intravenous bolus dose and two simulated serum concentrations per subject. In addition, a newer parametric expectation-maximisation (PEM) program with a Faure low discrepancy computation of the conditional likelihoods, as well as nonlinear mixed-effects modelling software (NONMEM), both the first-order (FO) and the FOCE versions, were used. For the second Monte Carlo study, a one-compartment model with an intravenous bolus dose was again used, with five simulated serum samples obtained from early to late after dosing. A unimodal distribution for V(d) and a bimodal distribution for k(e) were chosen to simulate two subpopulations of 'fast' and 'slow' metabolisers of a drug. NPEM results were compared with that of a unimodal parametric joint density having the true population parameter means and covariance. RESULTS: For the clinical dataset, the interindividual parameter percent coefficients of variation (CV%) were smallest with IT2B, suggesting less diversity in the population parameter distributions. However, the exact likelihood of the results was also smaller with IT2B, and was 14 logs greater with NPEM and NPAG, both of which found a greater and more likely diversity in the population studied.For the first Monte Carlo dataset, NPAG and PEM, both using accurate likelihood computations, showed statistical consistency. Consistency means that the more subjects studied, the closer the estimated parameter values approach the true values. NONMEM FOCE and NONMEM FO, as well as the IT2B FOCE methods, do not have this guarantee. Results obtained by IT2B FOCE, for example, often strayed visibly away from the true values as more subjects were studied. Furthermore, with respect to statistical efficiency (precision of parameter estimates), NPAG and PEM had good efficiency and precise parameter estimates, while precision suffered with NONMEM FOCE and IT2B FOCE, and severely so with NONMEM FO. For the second Monte Carlo dataset, NPEM closely approximated the true bimodal population joint density, while an exact parametric representation of an assumed joint unimodal density having the true population means, standard deviations and correlation gave a totally different picture. CONCLUSIONS: The smaller population interindividual CV% estimates with IT2B on the clinical dataset are probably the result of assuming Gaussian parameter distributions and/or of using the FOCE approximation. NPEM and NPAG, having no constraints on the shape of the population parameter distributions, and which compute the likelihood exactly and estimate parameter values with greater precision, detected the more likely greater diversity in the parameter values in the population studied. In the first Monte Carlo study, NPAG and PEM had more precise parameter estimates than either IT2B FOCE or NONMEM FOCE, as well as much more precise estimates than NONMEM FO. In the second Monte Carlo study, NPEM easily detected the bimodal parameter distribution at this initial step without requiring any further information. Population modelling methods using exact or accurate computations have more precise parameter estimation, better stochastic convergence properties and are, very importantly, statistically consistent. Nonparametric methods are better than parametric methods at analysing populations having unanticipated non-Gaussian or multimodal parameter distributions.     

Isoenzymatic identification of Leishmania isolates from repeated clinical human leishmaniasis episodes in Catalonia (Spain)

Forty human strains of Leishmania infantum isolated in 1985-99 from 17 patients with repeated cutaneous, mucosal or visceral leishmaniasis episodes in Catalonia (Spain) were examined by isoenzyme electrophoresis. Six zymodemes were revealed: MON-1, MON-24, MON-28, MON-29, MON-33 and MON-34. In 2 patients 2 different zymodemes were identified in consecutive episodes.