Circulatory model of vascular and interstitial distribution kinetics of rocuronium: a population analysis in patients

Distribution Clearance: Significance and Underlying Mechanisms

PURPOSE

Evaluation of distribution kinetics is a neglected aspect of pharmacokinetics. This study examines the utility of the model-independent parameter whole body distribution clearance (CLD) in this respect.

METHODS

Since mammillary compartmental models are widely used, CLD was calculated in terms of parameters of this model for 15 drugs. The underlying distribution processes were explored by assessment of relationships to pharmacokinetic parameters and covariates.

RESULTS

The model-independence of the definition of the parameter CLD allowed a comparison of distributional properties of different drugs and provided physiological insight. Significant changes in CLD were observed as a result of drug-drug interactions, transporter polymorphisms and a diseased state.

CONCLUSION

Total distribution clearance CLD is a useful parameter to evaluate distribution kinetics of drugs. Its estimation as an adjunct to the model-independent parameters clearance and steady-state volume of distribution is advocated.

Unusual Distribution Kinetics of Gadoxetate in Healthy Human Subjects Genotyped for OATP1B1: Application of Population Analysis and a Minimal Physiological-Based Pharmacokinetic Model

Gadoxetate (Gd-EOB-DTPA) is a hepatobiliary-specific contrast agent for magnetic resonance imaging. Using a minimal physiological-based pharmacokinetic (PBPK) model, it has been shown for the first time, that the rapid initial decline of plasma concentration after intravenous injection is the result of an uptake into hepatocytes rather than of a distribution into the extravascular extracellular space. About 50% of the steady-state distribution volume is related to hepatic uptake. The hepatic extraction ratio and hepatic clearance estimated based on the liver model as a part of the PBPK model were in accordance with literature data. The same holds for the predicted time course of the amount of gadoxetate in liver parenchyma. In elucidating the impact of OATP1B1 genotype (*1a/*1a and *15/*15) on the pharmacokinetics of gadoxetate, we found that tissue uptake and back-transfer rates were significantly reduced, whereas the hepatic sinusoidal efflux rate was significantly increased in carriers of the *15/*15 haplotype compared with those of the *1a/*1a (wild type). The model is potentially useful for determining hepatic kinetic parameters and distribution properties of drugs.

Human insulin dynamics in women: a physiologically based model

Currently available models of insulin dynamics are mostly based on the classical compartmental structure and, thus, their physiological utility is limited. In this work, we describe the development of a physiologically based model and its application to data from 154 patients who underwent an insulin-modified intravenous glucose tolerance test (IM-IVGTT). To determine the time profile of endogenous insulin delivery without using C-peptide data and to evaluate the transcapillary transport of insulin, the hepatosplanchnic, renal, and peripheral beds were incorporated into the circulatory model as separate subsystems. Physiologically reasonable population mean estimates were obtained for all estimated model parameters, including plasma volume, interstitial volume of the peripheral circulation (mainly skeletal muscle), uptake clearance into the interstitial space, hepatic and renal clearance, as well as total insulin delivery into plasma. The results indicate that, at a population level, the proposed physiologically based model provides a useful description of insulin disposition, which allows for the assessment of muscle insulin uptake.

Beta blockade increases pulmonary and systemic transit time heterogeneity: evaluation based on indocyanine green kinetics in healthy volunteers

Knowledge of factors influencing the heterogeneity of blood transit times is important in cardiovascular physiology. The aim of the study was to investigate the effect of beta-adrenergic blockade on blood transit time dispersion in awake, anxious volunteers. Recirculatory modelling of the disposition of intravascular markers using parametric forms for transit time distributions, such as the inverse Gaussian distribution, provides the opportunity to estimate the systemic and pulmonary transit time dispersion in vivo. The latter is determined by the flow heterogeneity in the microcirculatory network. Using this approach, we have analysed indocyanine green (ICG) disposition data obtained in four subjects by frequent early arterial blood sampling before and after beta-adrenergic blockade by propranolol. Propranolol decreased cardiac output from 9·3 ± 2·8 l min^-1 to 3·5 ± 0·47 l min^-1 (P<0·05). This reduction was accompanied by a 4·5 ± 0·6-fold and 2·1 ± 0·3-fold increase (P<0·001) in the relative dispersion (dimensionless variance) of blood transit times through the systemic and pulmonary circulation, respectively.

A reduction technique of arthroplasty without subtrochanteric femoral shortening osteotomy for the treatment of developmental high dislocation of hip: a case series of 28 hips

In total hip arthroplasty for the treatment of developmental dysplasia of the hip (DDH) with high hip dislocation, it can be technically challenging to locate the true acetabulum and restore limb length without subtrochantric femoral shortening osteotomy. We explored and described total hip arthroplasty without subtrochanteric femoral shortening osteotomy in 28 hips with Crowe type III and IV dislocation by intravenous injection of rocuronium at 0.9mg/kg 1minute before reduction and hip reduction combined with continuous strong traction of the affected limb with patients in a position with hip and knee flexion. All patients did not show dislocation, prosthesis loosening, and other severe complications. It is thus a safe and feasible reduction technique for arthroplasty of Crowe type III or IV dislocation of DDH.

In vivo measurement of extravasation of silver nanoparticles into liver extracellular space by push-pull-based continuous monitoring system

With the increasing prevalence of silver nanoparticles (AgNPs) in various products, whether such AgNPs will introduce new injury mechanisms from new pathologies remains to be determined. From the toxicokinetic viewpoint, it is vital to have in-depth knowledge of their in vivo transport kinetics and extravasation phenomenon. By combining push-pull perfusion sampling, in-tube solid phase extraction, and inductively coupled plasma mass spectrometry, we used an in vivo push-pull-based continuous monitoring system to investigate in vivo transport kinetics of extracellular AgNPs in living rat liver with a detection limit and temporal resolution of 0.64μgL(-1) and 10min, respectively. Before administration into living rats, the pre-incubation in DMEM with 10% FBS for 8h was adopted as the optimized exposure condition for the used AgNPs. After repeated-dose treatments, we observed a higher concentration of AgNPs in the liver extracellular space, suggesting that AgNP clearance by the reticuloendothelial system (RES) may be blocked by a prior administration of AgNPs. Future studies on AgNP distribution in different liver compartments (blood stream, extracellular space and Kupffer cells/hepatocytes) are necessary for defining the risks and benefits of AgNP applications.

Physiologically based structure of mean residence time

A mean residence time (MRT) is an important pharmacokinetic parameter. To the author's knowledge, however, a physiologically based structure of MRT (thereafter MRT structure) has not been published so far. Primarily this is because MRT structures cannot be identified by traditional pharmacokinetic methods used for the determination of MRT. Therefore, tools from the theory of linear dynamic systems were used for the structural identification of MRT in this study. The MRT structure identified is physiologically meaningful. Accordingly, it seems that the MRT structure identified may contribute to already established knowledge about MRT.

A physiologically based model of hepatic ICG clearance: interplay between sinusoidal uptake and biliary excretion

Although indocyanine green (ICG) has long been used for the assessment of liver function, the respective roles of sinusoidal uptake and canalicular excretion in determining hepatic ICG clearance remain unclear. Here this issue was addressed by incorporating a liver model into a minimal physiological model of ICG disposition that accounts of the early distribution phase after bolus injection. Arterial ICG concentration-time data from awake dogs under control conditions and from the same dogs while anesthetized with 3.5% isoflurane were subjected to population analysis. The results suggest that ICG elimination in dogs is uptake limited since it depends on hepatocellular uptake capacity and on biliary excretion but not on hepatic blood flow. Isoflurane caused a 63% reduction in cardiac output and a 33% decrease in the ICG biliary excretion rate constant (resulting in a 26% reduction in elimination clearance) while leaving unchanged the sinusoidal uptake rate. The terminal slope of the concentration-time curve, K, correlated significantly with elimination clearance. The model could be useful for assessing the functions of sinusoidal and canalicular ICG transporters.