Differences In Volume Of Distribution Research Articles

PET Imaging of Neuro-Inflammation with Tracers Targeting the Translocator Protein (TSPO), a Systematic Review: From Bench to Bedside

Parkinson's disease is the second most common neurodegenerative disorder, affecting 2-3% of the population of patients >65 years. Although the standard diagnosis of PD is clinical, neuroimaging plays a key role in the evaluation of patients who present symptoms related to neurodegenerative disorders. MRI, DAT-SPECT, and PET with [18F]-FDG are routinely used in the diagnosis and focus on the investigation of morphological changes, nigrostriatal degeneration or shifts in glucose metabolism in patients with parkinsonian syndromes. The aim of this study is to review the current PET radiotracers targeting TSPO, a transmembrane protein that is overexpressed by microglia in another pathophysiological process associated with neurodegenerative disorders known as neuroinflammation. To the best of our knowledge, neuroinflammation is present not only in PD but in many other neurodegenerative disorders, including AD, DLB, and MSA, as well as atypical parkinsonian syndromes. Therefore, in this study, specific patterns of microglial activation in PD and the differences in distribution volumes of these radiotracers in patients with PD as compared to other neurodegenerative disorders are reviewed.

1102. Evaluation of Vancomycin Accumulation in Patients with Obesity

BackgroundCurrent vancomycin guidelines recommend using actual body weight for dosing. However, in patients with obesity, this may result in lower initial vancomycin concentrations that can accumulate with continued doses due to differences in volume of distribution. The objective of this study is to evaluate the incidence of vancomycin accumulation in patients with obesity and identify potential factors associated with accumulation.MethodsThis is a single-center, retrospective, observational study at a tertiary academic medical center. Adult patients with a BMI ≥ 30 kg/m2 and with ≥ 2 vancomycin serum trough concentrations within the same encounter in 2019 were screened. Patients were excluded if they were pregnant, had unstable renal function or severe renal impairment, received < 3 doses before a concentration was drawn, or had inconsistent dosing prior to a concentration draw. Linear kinetics were used to correct for differences in timing of concentration or dose changes. The major endpoint was the incidence of vancomycin accumulation, defined as a 20% increase in trough concentration between the first and any subsequent trough concentrations within the first 10 days of therapy. Minor endpoints included the percentage of supratherapeutic concentrations and the incidence of acute kidney injury (AKI). Descriptive statistics were used to evaluate endpoints and multivariable logistic regression was used to evaluate factors associated with accumulation.ResultsWe screened 543 patients, and 162 were included in our analysis. The median age was 56.5 years (interquartile range [IQR] 43 - 65.3), and 62.3% were male. The median weight was 112.7 kg (IQR 99.8 - 122.6) and the median BMI was 36.8 kg/m2 (IQR 33.1 - 41). The median total daily vancomycin dose at initiation was 28.7 mg/kg/day (IQR 25.4 - 31.2). Vancomycin accumulation occurred in 99 patients (61.1%) within the first 10 days of therapy and AKI occurred in 21 patients (14.9%). No factors studied, including age, gender, obesity class, initial dose, SCr, or frequency were associated with accumulation.ConclusionMost patients with obesity experienced vancomycin accumulation within the first 10 days of therapy. Providers should be cautious when assessing a vancomycin concentration early in the treatment course.Disclosures All Authors: No reported disclosures

The pharmacokinetics of racemic MDPV and its (R) and (S) enantiomers in female and male rats

BackgroundThese studies investigated the serum pharmacokinetic (PK) profile of racemic (3,4)-methylenedioxypyrovalerone [(R,S)-MDPV)] and its (R)- and (S)-enantiomers in female and male Sprague Dawley rats. MethodsIntravenous (R,S)-MDPV (3 and 5.6mg/kg) and single enantiomer of (R)- and (S)-MDPV (1.5mg/kg) were administered to both sexes for PK studies. Intraperitoneal (ip) bioavailability was determined at 3mg/kg (R,S)-MDPV. Locomotor activity studies were conducted after ip treatment with saline and 0.3-5.6mg/kg of (R,S)-MDPV. ResultsPK values after iv (R,S)-MDPV showed a significant (p<0.05) sex-dependent differences in the volume of distribution at steady state (Vdss) for (R)- and (R,S)-MDPV at both (R,S)-MDPV doses. The female S/R enantiomeric ratios for area under the concentration time curve (AUCinf) and clearance were significantly lower and higher, respectively, than values determined in males. Importantly, there was no evidence of in vivo inversion of (R)-MDPV or (S)-MDPV to its antipode. There were, however, significant sex-dependent differences in volume of distribution after administration of the (R)-enantiomer. Bioavailability studies of ip (R,S)-MDPV showed greater variability and significantly greater bioavailability in male rats. Accordingly, there was a significantly greater maximal distance traveled measurement in male rats at a 3.0mg/kg dose. ConclusionPK sex differences in (R,S)-MDPV and enantiomers were most apparent in volume of distribution, which could be caused by differences in drug blood and tissue protein binding. The increased magnitude and variance in ip bioavailability in male compared to female rats could lead to sex-dependent differences in the pharmacological action caused by active enantiomer (S)-MDPV.

Abstract 2851: Cellular glutamine pool size change in response to glutaminase inhibition detected by kinetic analysis of [18F](2S,4R)4-fluoroglutamine PET

Abstract INTRODUCTION Oncogene-dependent reliance on glutamine is a cancer vulnerability that can be exploited for therapeutic gain. Inhibitors of glutaminase, the enzyme that catalyzes the conversion of glutamine to glutamate, have been developed and have shown antitumor effects in several tumor models. The specific and potent glutaminase inhibitor CB-839 demonstrated marked antitumor efficacy in a triple-negative breast cancer (TNBC) cell line with inherently high glutaminase activity (HCC-1806), but not in an estrogen receptor-positive (ER+) cell line with inherently low glutaminase activity. An early phase 1 clinical trial of CB-839 in combination with paclitaxel has shown encouraging results in TNBC patients. Cell-line specific efficacy of glutaminase inhibitors supports the need for clinical biomarkers that can predict and evaluate therapeutic efficacy. As a minimally metabolized glutamine analog with similar transport properties, [18F](2S,4R)4-Fluoroglutamine ([18F]4F-Gln) is an ideal radiotracer to infer glutamine pool size through estimates of tracer distribution volume (DV). In this study, we demonstrate differences in DV of [18F]4F-Gln in two xenografts with different levels of glutaminolysis (TNBC vs. ER+) using dynamic PET imaging, as well as show the effect of anti-glutaminase therapy on [18F]4F-Gln DV. METHODS TNBC (HCC-1806) and ER+ (MCF-7) xenografts were established in athymic nu/nu mice. Mice were scanned in a dedicated animal PET scanner at baseline and after CB-839 administration. Dynamic imaging was obtained for one hour upon injection of [18F]4F-Gln (300-350 μCi) via the tail vein. Kinetic analysis was performed with PMOD. RESULTS [18F]4F-Gln uptake was largely reversible with Logan plots demonstrating late linearity and k3 in a two-compartment (trapping) model was low (less than 0.01/min in most cases). Strong correlation was seen in DV estimates by Logan plot and a single-compartmental model (R2&amp;gt;0.9), but not with estimates from a two-compartment model. MCF-7 xenografts demonstrated greater than 60% larger DV at baseline than TNBC xenografts indicative of increased cellular glutamine concentrations in MCF-7 xenografts. An increase in DV was detected in TNBC xenografts post-glutaminase inhibition (&amp;gt;30% mean change), but not in MCF-7 xenografts. CONCLUSION Estimates of [18F]4F-Gln DV offer the ability to non-invasively infer tumor glutaminolysis. Low [18F]4F-Gln uptake in highly glutaminolytic tumors and an increase in [18F]4F-Gln uptake with glutaminase inhibition is concordant with changes in cellular glutamine concentration as measured by MR spectroscopy of tumor extracts. Our studies indicate promise for the use of [18F]4F-Gln as a predictive and pharmacodynamic marker for glutaminase-targeted therapy. Supported by: Komen SAC130060, DE-SE0012476, R21-CA198563 We thank Calithera Inc. for providing CB-839 and Dr. Susan Demo for discussions. Citation Format: Austin R. Pantel, Hsiaoju Lee, Shihong Li, Robert K. Doot, Robert H. Mach, David A. Mankoff, Rong Zhou. Cellular glutamine pool size change in response to glutaminase inhibition detected by kinetic analysis of [18F](2S,4R)4-fluoroglutamine PET [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2851. doi:10.1158/1538-7445.AM2017-2851

Insulin kinetics and the Neonatal Intensive Care Insulin–Nutrition–Glucose (NICING) model

BackgroundModels of human glucose–insulin physiology have been developed for a range of uses, with similarly different levels of complexity and accuracy. STAR (Stochastic Targeted) is a model-based approach to glycaemic control. Elevated blood glucose concentrations (hyperglycaemia) are a common complication of stress and prematurity in very premature infants, and have been associated with worsened outcomes and higher mortality. This research identifies and validates the model parameters for model-based glycaemic control in neonatal intensive care. MethodsC-peptide, plasma insulin, and BG from a cohort of 41 extremely pre-term (median age 27.2 [26.2–28.7] weeks) and very low birth weight infants (median birth weight 839 [735–1000] g) are used alongside C-peptide kinetic models to identify model parameters associated with insulin kinetics in the NICING (Neonatal Intensive Care Insulin–Nutrition–Glucose) model. A literature analysis is used to determine models of kidney clearance and body fluid compartment volumes. The full, final NICING model is validated by fitting the model to a cohort of 160 glucose, insulin, and nutrition data records from extremely premature infants from two different NICUs (neonatal intensive care units). ResultsSix model parameters related to insulin kinetics were identified. The resulting NICING model is more physiologically descriptive than prior model iterations, including clearance pathways of insulin via the liver and kidney, rather than a lumped parameter. In addition, insulin diffusion between plasma and interstitial spaces is evaluated, with differences in distribution volume taken into consideration for each of these spaces. The NICING model was shown to fit clinical data well, with a low model fit error similar to that of previous model iterations. ConclusionsInsulin kinetic parameters have been identified, and the NICING model is presented for glycaemic control neonatal intensive care. The resulting NICING model is more complex and physiologically relevant, with no loss in bedside-identifiability or ability to capture and predict metabolic dynamics.

Gender differences in pharmacokinetics and pharmacodynamics of methadone substitution therapy.

Gender-related differences in the pharmacological effects of drug are an emerging topic. This review examines gender differences in both pharmacokinetic and pharmacodynamic aspects of methadone, a long-acting opioid agonist that is prescribed as a treatment for opioid dependence and the management of chronic pain.Method: We performed a search in the Medline database from 1990 to 2014 in order to find published literature related to gender differences in pharmacokinetics (PK) and pharmacodynamics (PD) of methadone.Results: None of the studies were carried out with the primary or secondary aim to identify any gender differences in the pharmacokinetic profile of methadone. Importantly; high inter-subjects variability in PK parameters was found also intra female population. The reported differences in volume of distribution could be ascribed to the physiological differences between men and women in body weight and composition, taking into account that the dose of methadone was established irrespective of body weight of patients (Peles and Adelson, 2006). On the other hand, the few studies present in literature found no gender difference in some direct pharmacodynamic parameters. Some reports have suggested that female gender is associated with an increased risk for long-QT-related cardiac arrhythmias in methadone maintenance subjects.Conclusion: Even though it may be too simplistic to expect variability only in one parameter to explain inter-individual variation in methadone response, we believe that a better knowledge of gender-related differences might have significant implications for better outcomes in opioid dependence substitution therapy in women.

Antimicrobial Distribution From Local Delivery Depends on Dose

Tissue distribution after local delivery has been quantified over a period of 5 hours on 7-T MRI in a rabbit model using gadolinium-labeled diethylenetriamine pentaacetic acid (Gd-DTPA) as an antimicrobial surrogate; however, it is unknown how the Gd-DTPA load in a local depot will affect the duration of high-concentration Gd-DTPA in local tissues after surgical débridement. We determined whether the Gd-DTPA load in bone cement affected its local tissue distribution over a period of 1 month after local delivery. A 1-cm3 soft tissue dead space was created in the quadriceps of seven rabbits and filled with gadolinium-loaded bone cement. At 7, 14, and 33 days, the volume of tissue with a Gd-DTPA concentration of more than 14 μg/mL was calculated from T1-weighted images using 7-T MRI. Differences in volumes of distribution were analyzed with ANOVA. The volume of tissue with more than 14 μg/mL Gd-DTPA was much larger from higher gadolinium loads on Day 7 (p=0.02) (2121 mm3 for 10 g and 665 mm3 for 1 g) and smaller with time for the 10-g formulation (2121 mm3 on Day 7 and 1241 mm3 on Day 14). Volume of distribution and duration of Gd-DTPA after local delivery increased with increasing load in the cement and decreased with time. For local delivery, high antimicrobial concentrations would be expected in greater volumes of tissue, for longer durations, when higher antimicrobial loads are used.

H1‐antihistamines and urticaria: how can we predict the best drug for our patient?

Urticaria, and especially chronic spontaneous urticaria (CSU), is a difficult condition to treat. Consequently, clinicians need to use the best H(1)-antihistamines currently available and the pharmaceutical industries need to keep developing H(1)-antihistamines that are more effective than the ones we have today. To do this we need to be able to compare the clinical efficacy of both established and new drugs. Obviously, the ideal way to do this is to use head-to-head studies in CSU. However, such studies are extremely expensive and, in the case of novel molecules, have ethical and logistical problems. Consequently, we need to have predictive models. Although determination of Ki, an indicator of the in vitro potency of an H(1)-antihistamine, may help in the initial selection of candidate molecules, the large differences in volume of distribution and tissue accumulation in humans, precludes this from being a good predictor of clinical efficacy in CSU. From the data reviewed in this article, especially the direct comparative data of desloratadine and levocetirizine in weal and flare studies and CSU, weal and flare response would appear to be the best indicator we have of effectiveness of H(1)-antihistamines in clinical practice. However, it must be pointed out that the conclusion is, essentially, based on detailed comparisons of two drugs in studies sponsored by pharmaceutical companies. Consequently, to confirm the conclusions of this review, a multicentre study independent from the influence of pharmaceutical companies should be commissioned to compare the speed of onset and effectiveness of desloratadine, fexofenadine and levocetirizine in chronic spontaneous urticaria and against histamine-induced weal and flare responses in the same patients so that we have a clear understanding of the predictive value of our models.

Quinine impairs quinidine clearance in rat perfused liver.

We have examined the disposition of the cinchona alkaloids quinine and quinidine in the rat recirculating isolated perfused liver preparation. When administered as separate 1 mg doses, the hepatic clearances of quinine and quinidine were similar to the hepatic perfusate rate of 10 mL min-1. When 1 mg of each was administered simultaneously, mean hepatic clearance of quinine was unchanged (9.00 +/- 2.20 mL min-1 separate dosage, n = 7; 6.87 +/- 1.77 mL min-1 simultaneous dosage, n = 7; P > 0.05). By contrast, mean hepatic clearance of quinidine was reduced significantly by concomitant quinine (10.6 +/- 1.72 mL min-1 separate dosage, n = 7; 4.82 +/- 1.25 mL min-1 simultaneous dosage, n = 7; P < 0.05). There was no significant difference in volumes of distribution when each alkaloid was administered separately (131 +/- 46 mL quinine, 129 +/- 21 mL quinidine; P > 0.05) but concomitant quinine administration increased quinidine volume of distribution to 169 +/- 30 mL (P < 0.05). Four further experiments with simultaneous dosages of 0.5 mg of each alkaloid produced similar findings, indicating that the interactions did not derive from nonlinear drug disposition.

Pharmacokinetic Interactions Between Isoniazid and Theophylline in Rats

Pharmacokinetic interactions between isoniazid and theophylline were studied in male Wistar rats, 206 +/- 17 g. Concomitant oral administration of 2 x 5 mg kg-1 isoniazid accelerated slightly the disposition of theophylline (10 mg kg-1, i.v.) whereas 2 x 25 mg kg-1 isoniazid slowed it marginally. The differences in distribution volume, systemic clearance and area under the concentration-time curve (AUC) between the high and the low dose, however, were statistically significant. One week pretreatment with 10 mg kg-1 isoniazid tended towards inhibition (significant decrease of systemic clearance, increase of AUC) and 50 mg kg-1 to acceleration (decrease of half-life, mean residence time and AUC, increase of systemic clearance) of theophylline disposition. After oral pretreatment with 20 mg kg-1 theophylline, neither the kinetics of free isoniazid (50 mg kg-1, i.v.) and the amount acetylated nor the acetylation indices differed from the controls. There was no evidence that concomitant or subacute administration of different doses of isoniazid affects major metabolic pathways of theophylline or that prolonged theophylline treatment interacts with the N-acetylation capacity.

Pharmacokinetics of vancomycin in neonates admitted to the neonatology unit at the Jordan University Hospital

Vancomycin is used in neonatal intensive care units to treat nosocomial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) or coagulase-negative staphylococci. Current dosing regimens are not adequate, producing trough concentrations below the target range. 151 neonates who received vancomycin and had vancomycin peak and trough concentration measurements as part of regular therapeutic drug monitoring were utilized. The patients were divided into three groups according to gestational age; less than 28 weeks, 28 to less than 34 weeks and 34 weeks to term. Neonates were given vancomycin doses as per guidelines. The pharmacokinetic parameters, elimination rate constant (K), elimination half-life (t1/2), volume of distribution (VD) and clearance (CL), were calculated. Peak vancomycin concentrations ranged from 9.4 to 52.8 mg/l, while troughs ranged from 0.0 to 16.6 mg/l. One third of the trough concentrations were below 5 mg/l and are thus, subtherapeutic. There were no statistically significant differences between the three groups in regard to elimination rate constant and half-life. However, there was a statistically significant difference in volume of distribution between the three groups (p < 0.05), and in clearance between the first group and the other two (p < 0.05), using Kruskal-Wallis statistical test. The empirical dosing method used was inadequate in one third of patients. Individualization of vancomycin dosing in the neonatal critical care unit at The Jordan University Hospital seems necessary.

Gender Differences in the Pharmacokinetics of Oral Drugs

Establishment of rational dosage regimens requires the knowledge of pharmacokinetics and pharmacodynamics in the target population. It has been established that side effects produced by drugs are more frequent in women than in men. This may be due to two possibilities, one is that normalized dose received by women is higher than men and the other is that anatomical and physiological characteristics are a quite different. In this review, some aspects that may play a role in the generation of such differences are analyzed, including the impact on absorption, distribution, metabolism and excretion of drugs. Most of the changes can be explained by differences in volume of distribution and systemic clear- ance, however, presystemic clearance also seems to play a role in such dissimilarities. The final result, in general, is that women have higher plasma levels of drugs and usually these differences are reduced or abolished when data are normalized by the body weight, since both, volume of distribution and systemic clearance are influenced by it; however, there are some cases in which differences remain. Further research oriented to establish the role of each of the ana- tomical and physiological differences in the oral pharmacokinetics of drugs is warranted.

Trabectedin in pre-treated patients with advanced or metastatic soft tissue sarcoma: a phase II study evaluating co-treatment with dexamethasone

This study assesses the efficacy, toxicity and pharmacokinetic profile of trabectedin with or without prophylactic dexamethasone co-treatment in patients with recurrent advanced soft tissue sarcoma (STS). Patients were randomized to receive trabectedin as a 3-h infusion every 3 weeks with dexamethasone or placebo in the first cycle, with the alternate in the second cycle and with the patient's choice subsequently. Due to toxicity, the randomized design was modified to open-label to make dexamethasone mandatory and the initial dose (1,650 μg/m(2)) was reduced to 1,500 μg/m(2) and then to 1,300 μg/m(2). Forty-one patients were enrolled and 35 were evaluable for efficacy. One partial response and 18 disease stabilizations were found. The median PFS and OS were 2.1 and 10.2 months, respectively, with the 3- and 6-month PFS rates indicating activity in pretreated STS. Twenty-three and 27 patients developed transient asymptomatic grade 3/4 AST and ALT elevation, respectively, and 21 patients had grade 3/4 neutropenia. Dose reduction from 1,650 μg/m(2) to 1,300 μg/m(2) decreased the incidence of grade 3/4 thrombocytopenia (26% vs. 0%), neutropenia (51% vs. 25%) and AST increase (76% vs. 25% of patients). Four patients died due to drug-related toxicities (3 with placebo). The total body clearance of trabectedin was 28% higher and half-life was 21% lower with dexamethasone compared to placebo, with no differences in volume of distribution. Trabectedin has confirmed activity in patients with pretreated STS. This study shows that co-treatment with dexamethasone improves the safety of trabectedin by reducing drug-induced hepatotoxicity and myelosuppression.

Modelling of patient EMS exposure: Translating pharmacokinetics of EMS in vitro and in animals into patients

In order to support the toxicological risk assessment for the ethyl methanesulfonate (EMS) exposure of patients ingesting contaminated Viracept tablets (Müller and Singer, 2009), there was a need to correlate the effects observed in in vivo genotoxicity studies with mice to EMS exposure and to estimate human exposure to EMS at the level of contamination of Viracept tablets. The species differences in volume of distribution of EMS, a key factor for determination of its C max, were small in the species investigated (mouse, rat, monkey), the species differences in clearance, the key factor involved in AUC assessment, were large (Lavé et al., 2009). Because of this uncertainty in extrapolation of clearance across species we used a conservative approach for human exposure predictions in terms of AUC where clearance was assumed to solely reflect the chemical stability of EMS neglecting additional clearance pathways such as metabolism and exhalation. This approach was compared to the estimates obtained from allometric scaling based on rat clearance, the species leading to the lowest clearance predicted in man. We found that both approaches led to nearly identical predictions of the human AUC. Thus, we predict a human AUC of 13 μM h for patients ingesting the most contaminated Viracept tablets, corresponding to a maximal daily intake of 0.055 mg/kg of EMS. The C max of EMS in these patients is predicted to be 0.85 μM. In order to provide a basis for toxicological risk assessment, these maximal human AUC and C max values are to be compared to the AUC and C max values in mice at the EMS dose of 25 mg/kg which was found to be the threshold dose for induction of mutagenic effects, i.e. the dose at which no mutagenic effects were observed (Gocke et al., 2009-a). We calculate AUC and C max in mice at the threshold dose to be 350 μM h and 315 μM, respectively. Thus we conclude that a large safety factor can be deduced, whatever the basis of comparison, as is discussed in detail by Müller et al. (2009).

Impact of obesity on oral contraceptive pharmacokinetics and hypothalamic–pituitary–ovarian activity

Background This study was conducted to determine whether increased body mass index (BMI) affects oral contraceptive (OC) pharmacokinetics and suppression of hypothalamic–pituitary–ovarian (HPO) axis activity. Study Design Ovulatory reproductive-age women with normal weight (BMI <25 kg/m 2; n=10) and with obesity (BMI >30 kg/m 2; n=10) received OCs for two cycles (prospective cohort). Subjects were admitted for two 48-h inpatient stays at the beginning and end of the hormone-free interval. Ethinyl estradiol and levonorgestrel (LNG) levels were evaluated during both inpatient stays. Gonadotropin pulsatility (follicle-stimulating hormone and luteinizing hormone) was measured during the second inpatient stay. Estradiol (E 2) and progesterone (P) were measured daily during inpatient stays and twice per week in Cycle 2. Results BMI was greater in the obese compared to the normal-BMI group [37.3 kg/m 2 (SD, 6.0) vs. 21.9 kg/m 2 (SD, 1.6); p<.05]. The LNG half-life was significantly longer in the obese group (52.1±29.4 vs. 25.6±9.3 h, p<.05), which correlated with a lower maximum LNG concentration on Cycle 2, Day 1 [1.9 ng/mL (SD, 0.5) vs. 2.5 ng/mL (SD, 0.7)] and a longer time to reach steady state (10 vs. 5 days) in obese women. There were no significant differences in volume of distribution between groups. LH pulse parameters did not differ statistically between groups but trended toward greater HPO activity in the obese group. Additionally, more obese (6/10 vs. 3/10 normal BMI, p>.05) women exhibited E 2 levels consistent with development of a dominant follicle and P levels consistent with ovulation (2/10 vs. 1/10) during Cycle 2. Conclusions Compared to women with normal BMI, obese women exhibit differences in OC pharmacokinetics that are associated with greater HPO activity.

Pharmacokinetics of gadoversetamide injection, a gadolinium-based contrast agent, in pediatric patients

The pharmacokinetics of gadoversetamide were examined in pediatric patients scheduled to undergo contrast-enhanced MRI of the central nervous system. One hundred patients received an intravenous injection of gadoversetamide at a dose of 0.1 mmol/kg for a contrast-enhanced MRI procedure. A subpopulation of 30 patients were enrolled to evaluate the pharmacokinetics of gadoversetamide in patients 2-11 and 12-18 years of age. Serial blood and urine samples were collected before and after the administration of gadoversetamide. The terminal half-life, initial concentration and area under the curve assessments for gadoversetamide showed no significant (P>.05) differences between the age groups or the sexes. Although no sex-related differences occurred in the volume of distribution or clearance, significant (P<.05) age-related differences were found, but once corrected for body mass or surface area the differences were no longer significant. The pharmacokinetic behavior of gadoversetamide was not significantly altered by differences in age or sex in pediatric patients from 2 to 18 years of age. Although significant differences in volumes of distribution, and clearance occurred between the age groups, these differences appeared to depend on body size rather than on age in pediatric patients between 2 and 18 years of age.

Real-time imaging of convection-enhanced delivery of viruses and virus-sized particles

Despite recent evidence showing that convection-enhanced delivery (CED) of viruses and virus-sized particles to the central nervous system (CNS) is possible, little is known about the factors influencing distribution of these vectors with convection. To better define the delivery of viruses and virus-sized particles in the CNS, and to determine optimal parameters for infusion, the authors coinfused adeno-associated virus ([AAV], 24-nm diameter) and/or ferumoxtran-10 (24 nm) by using CED during real-time magnetic resonance (MR) imaging. Sixteen rats underwent intrastriatal convective coinfusion with 4 microl of 35S-AAV capsids (0.5-1.0 x 10(14) viral particles/ml) and increasing concentrations (0.1, 0.5, 1, and 5 mg/ml) of a similar sized iron oxide MR imaging agent (ferumoxtran-10). Five nonhuman primates underwent either convective coinfusion of 35S-AAV capsids and 1 mg/ml ferumoxtran-10 (striatum, one animal) or infusion of 1 mg/ml ferumoxtran-10 alone (striatum in two animals; frontal white matter in two). Clinical effects, MR imaging studies, quantitative autoradiography, and histological data were analyzed. Real-time, T2-weighted MR imaging of ferumoxtran-10 during infusion revealed a clearly defined hypointense region of perfusion. Quantitative autoradiography confirmed that MR imaging of ferumoxtran-10 at a concentration of 1 mg/ml accurately tracked viral capsid distribution in the rat and primate brain (the mean difference in volume of distribution [Vd] was 7 and 15% in rats and primates, respectively). The Vd increased linearly with increasing volume of infusion (Vi) (R2 = 0.98). The mean Vd/Vi ratio was 4.1 +/- 0.2 (mean +/- standard error of the mean) in gray and 2.3 +/- 0.1 in white matter (p < 0.01). The distribution of infusate was homogeneous. Postinfusion MR imaging revealed leakback along the cannula track at infusion rates greater than 1.5 microl/minute in primate gray and white matter. No animal had clinical or histological evidence of toxicity. The CED method can be used to deliver AAV capsids and similar sized particles to the CNS safely and effectively over clinically relevant volumes. Moreover, real-time MR imaging of ferumoxtran-10 during infusion reveals that AAV capsids and similar sized particles have different convective delivery properties than smaller proteins and other compounds.

PET Imaging of CRF1 with [11C]R121920 and [11C]DMP696: is the target of sufficient density?

Overstimulation of the CRF type 1 receptor (CRF1) is implicated in anxiety and depressive disorders. The aim of this study was to investigate the in vivo binding characteristics of [11C]R121920 and [11C]DMP696 in the nonhuman primate for application in positron emission tomography (PET) studies of CRF1. PET imaging with the two novel CRF1 radioligands was performed in baboon. In vitro binding studies for CRF1 were performed in postmortem brain tissue of baboon and human to assess sufficiency of receptor density for PET. Both [11C]R121920 and [11C]DMP696 distributed rapidly and uniformly throughout the brain. Washout was comparable across brain regions, without differences in volume of distribution between regions reported to have high and low in vitro CRF1 binding. Membrane-enriched tissue homogenate assay using [(125)I]Tyr(0)-sauvagine and specific CRF1 antagonists CP154,526 and SN003 in human occipital cortex yielded maximal binding (Bmax) of 63.3 and 147.3 fmol/mg protein, respectively, and in human cerebellar cortex yielded Bmax of 103.6 and 64.6 fmol/mg protein, respectively. Dissociation constants (K(D)) were subnanomolar. In baboon, specific binding was not detectable in the same regions; therefore, Bmax and K(D) were not measurable. Autoradiographic results were consistent except there was also detectable CRF1-specific binding in baboon cerebellum. Neither [11C]R121920 nor [11C]DMP696 demonstrated quantifiable regional binding in vivo in baboon. In vitro results suggest CRF1 density in baboon may be insufficient for PET. Studies in man may generate more promising results due to the higher CRF1 density compared with baboon in cerebral cortex and cerebellum.

Enantiomer–enantiomer interaction of ifosfamide in the rat

The objective of this study was to study the enantiomer–enantiomer interaction of ifosfamide (IFA) in a rat model. Following intravenous administration of individual IFA enantiomers or pseudo-racemates to male Sprague–Dawley rats, two enantiomers and their metabolites, 4-hydroxyIF (HOIF), N2-dechloroethylIF (N2D), N3-dechloroethylIF (N3D), and isophosphoramide (IPM), were quantified using gas chromatography/mass spectrometry (GC/MS) and isotope dilution techniques. In addition, the mutual inhibition in the metabolism between two stereoisomers was also investigated in vitro using rat liver microsomes. Pharmacokinetic parameters were similar between (R)-IFA and (S)-IFA when individual enantiomers were intravenously administered to rats separately. However, in the rats administered with the IFA racemate, half-life, mean residence time (MRT), and area under the concentration–time curve (AUC) values of (S)-IFA were significantly increased with total body clearance (CLT) being decreased. No significant difference in volumes of distribution (Vss), and renal clearance (CLr) and blood cell partition was observed between two enantiomers regardless of (R)-IFA and (S)-IFA being administered separately or in combination as a racemate. The results from the in vitro metabolism and inhibition experiment suggested that each IFA enantiomer inhibited the metabolism of its antipode in a competitive manner. It is concluded that the enantiomeric interaction of IFA mainly occurred in the process of metabolism with (S)-IFA being affected to a larger extent.

Diazoxide‐mediated insulin suppression in obese men: a dose‐response study*

It has been suggested that diazoxide (DZX)-mediated insulin suppression may be useful to promote weight loss in obese subjects. To assess the DZX-dose range that is safe to use in obese hyperinsulinaemic men. Assessment of DZX efficacy and safety was based on plasma glucose and insulin responses to a standardized 500-kcal breakfast, taken on the sixth day of treatment. Basic information regarding the potential efficacy of DZX treatment was first evaluated in an open-label study in five non-obese men. Subsequently, a double-blind, randomized, placebo-controlled study was performed in 12 obese but otherwise healthy men, comparing placebo treatment with DZX in doses of 50, 75 and 100 mg three times daily for 6 days. In non-obese subjects, DZX 50 mg decreased peak insulin levels by +/-28% and raised peak glucose concentration from 7.1 +/- 0.6 to 7.8 +/- 0.6 mmol/l (p < 0.05). DZX 100 mg reduced peak insulin levels by 45% and caused a rise in peak glucose levels from 7.1 +/- 0.6 to 9.0 +/- 0.9 mmol/l (p < 0.05). In obese men, the 50 and 75 mg doses had no significant effects on glucose or insulin levels. DZX 100 mg reduced the peak insulin levels and insulin area under the curve by +/-20% (p < 0.05) but did not affect fasting or postprandial glucose levels. The relatively limited insulin-suppressive effects in obese subjects were attributed to the low plasma DZX levels that were achieved in this group. For comparable doses, plasma DZX levels were about 30% lower in obese than in non-obese men. Plasma DZX levels were highly dependent on dose (p < 0.001) and body weight (p < 0.001). Ninety-two percent of the total variability in DZX levels was explained by these two parameters. DZX-mediated insulin suppression is dose dependent in normal and in obese men. However, the efficacy of DZX is much less in obese than in non-obese subjects. This is attributed to weight-dependent differences in distribution volume that lead to markedly lower plasma DZX levels in obese subjects. Weight-adjusted doses will be needed to achieve biologically effective plasma DZX levels. Extrapolation of the data suggests that effective insulin suppression in obese men will at least require a daily dose of 3.2-4.2 mg/kg.