In vitro in vivo relations for the parenteral liposomal formulation of Amphotericin B: A biorelevant and clinically relevant approach.

There is limited information on how to perform in vitro release tests for intravenously administered parenteral formulations and how to relate the in vitro release with an in vivo pharmacokinetic parameter after the administration of the formulation. In this study, the effect of hydrodynamics (using sample and separate and continuous flow conditions) and medium components (synthetic surfactants, albumin and buffers) on the release of Amphotericin B from the liposomal Ambisome® formulation were investigated. Pharmacokinetic modeling of plasma concentration profiles from healthy subjects administered Ambisome® was used to estimate the in vivo release rate constant of drug from the formulation in order to compare it with the in vitro release profiles. With the estimated in vivo and in vitro release rate constants, release profiles were generated. Two approaches were followed: comparison of in vivo and in vitro release rate constants and comparison of the area under the percent release-time curve from observed in vitro release data and simulated in vivo release data. Albumin was found to be most critical factor for the release of the drug by having a negative effect on the amount of Amphotericin B released. The release profiles obtained with the sample and separate method in both Krebs Ringer buffer- and Phosphate Saline buffer - albumin 4.0% w/v were predictive of the in vivo release profiles in healthy subjects. Determining the factors affecting drug release from parenteral formulations and relating the release profiles to a pharmacokinetic parameter in vivo supports the development of in vitro in vivo relations for parenteral products.

In vitro - in vivo relations for the parenteral liposomal formulation of Amphotericin B: A clinically relevant approach with PBPK modeling.

In vitro release testing is a useful tool for the quality control of controlled release parenteral formulations, but in vitro release test conditions that reflect or are able to predict the in vivo performance are advantageous. Therefore, it is important to investigate the factors that could affect drug release from formulations and relate them to in vivo performance. In this study the effect of media composition including albumin presence, type of buffer and hydrodynamics on drug release were evaluated on a liposomal Amphotericin B formulation (Ambisome®). A physiologically based pharmacokinetic (PBPK) model was developed using plasma concentration profiles from healthy subjects, in order to investigate the impact of each variable from the in vitro release tests on the prediction of the in vivo performance. It was found that albumin presence was the most important factor for the release of Amphotericin B from Ambisome®; both hydrodynamics setups, coupled with the PBPK model, had comparable predictive ability for simulating in vivo plasma concentration profiles. The PBPK model was extrapolated to a hypothetical hypoalbuminaemic population and the Amphotericin B plasma concentration and its activity against fungal cells were simulated. Selected in vitro release tests for these controlled release parenteral formulations were able to predict the in vivo AmB exposure, and this PBPK driven approach to release test development could benefit development of such formulations.

Population pharmacokinetics of teicoplanin and attainment of pharmacokinetic/pharmacodynamic targets in adult patients with haematological malignancy.

OBJECTIVES: To describe the population pharmacokinetics of teicoplanin in adult patients with haematological malignancies receiving higher than standard doses, and to perform Monte Carlo simulations to determine dosing regimens associated with optimal teicoplanin concentrations. METHODS: This was a hospital-based clinical trial (EudraCT 2013-004535-72). Nine blood samples were collected on Day 3, plus single trough samples on Days 7 and 10, and 24 and 48 hours after the last dose. Teicoplanin minimum inhibitory concentrations were determined for Gram-positive isolates from study patients. Population pharmacokinetic analyses and Monte Carlo dosing simulations were undertaken using Pmetrics. RESULTS: Thirty adult haematological malignancy patients were recruited with a mean (SD) loading dose, age, total body weight, and creatinine clearance of 9.5 (1.9) mg/kg, 63 (12) years, 69.1 (15.8) kg, and 72 (41) mL/min, respectively. A three-compartment linear pharmacokinetic model best described the teicoplanin concentration data. Covariates supported for inclusion in the final model were creatinine clearance for clearance and total body weight for volume of the central compartment. The median (IQR) area under the concentration-time curve from 48 to 72 hours (AUC48-72h) was 679 (319) mg.h/L. There was a strong correlation between the AUC48-72h and trough concentration at 72 hours (Pearson correlation coefficient 0.957, p <0.001). Dosing simulations showed that administration of five loading doses at 12-hourly intervals, stratified by total body weight and creatinine clearance, increased the probability of achieving target concentrations within 72 hours. CONCLUSIONS: To increase the number of patients achieving optimal teicoplanin concentrations an individualized dosing approach, based on body weight and creatinine clearance, is recommended.

Hydrodynamic simulation (computational fluid dynamics) of asymmetrically positioned tablets in the paddle dissolution apparatus: impact on dissolution rate and variability.

The aim of this work was to investigate the dissolution rate from both the curved and planar surfaces of cylindrical compacts of benzoic acid, which were placed centrally and non-centrally at the base of the vessel of the paddle dissolution apparatus. The effect of fixing the compacts to a particular position on the variability of dissolution results was also examined. In addition, computational fluid dynamics (CFD) was used to simulate fluid flow around compacts in the different positions in the vessel, and the relationship between the local hydrodynamics in the region of the compacts and the dissolution rate determined. The dissolution rate was found to increase from the centre position to the off-centre positions for each surface examined. There was a corresponding increase in maximum fluid velocities calculated from the CFD fluid flow simulations at a fixed distance from the compact. There was less variability in dissolution from compacts fixed to any of the positions compared with those that were not fixed. Fluid flow around compacts in different positions could be successfully modelled, and hydrodynamic variability examined, using CFD. The effect of asymmetric fluid flow was evident visually from the change in shape of the eroded compacts.

A longitudinal analysis of cytotoxic T lymphocyte precursor frequencies to the hepatitis B virus in chronically infected patients.

Individuals with acute hepatitis B virus (HBV) infection characteristically mount a strong, multispecific cytotoxic T lymphocyte (CTL) response that is effective in eradicating virus. In contrast, this response in chronic carriers is usually weak or undetectable. Since it is generally acknowledged that HBV pathogenesis is immune-mediated, the occurrence of episodes of active liver disease in many carriers suggests that these individuals can mount active CTL responses to HBV. To see whether the detection of circulating CTLs is related to these flare episodes, we have determined the CTL precursor (CTLp) frequencies to HLA-A2-restricted viral peptides in seven patients over a 12-24-month period of their disease. Limiting dilution analyses (LDA) were performed longitudinally to five epitopes comprising the viral capsid (HBc), envelope (HBs) and polymerase (pol) proteins. Assays were performed against a mixture of peptides, or against each individual peptide, to measure overall CTL activity and the multispecificity of the responses, respectively. Since two of the patients were treated with recombinant human interleukin-12 (rHuIL-12) at the time, with one individual achieving complete disease remission a year later after being treated with interferon-alpha, we were also able to examine the effects of these cytokines on HBV cytotoxicity. Our results indicate that weak but detectable CTL responses do occur in chronic carriers which are generally associated with disease flares, although CTLps were also seen occasionally during minimal disease activity. The range of specificities varied between individuals and within each individual during the course of the disease. Finally, we also provide evidence that CTL reactivity is stimulated following treatment with certain cytokines, but is dependent on the time of administration.