A critical study on borosilicate glassware and silica-based QMA's in nucleophilic substitution with [18F]fluoride: influence of aluminum, boron and silicon on the reactivity of [18F]fluoride.

Leachables of borosilicate glassware and silica-based anion exchange columns (QMAs) may influence nucleophilic substitution with [(18)F]fluoride ([(18)F]F(-)). Aluminum, boron and silicon, all constituents of borosilicate glass, were found as water soluble leachables in a typical PET synthesis setup. Relevant ranges of the leachable quantities were studied based on an experimental design, in which species of the three elements were added to the labeling of the precursor for anti-1-amino-3-[(18)F]fluorocyclobutyl-1-carboxylic acid ([(18)F]FACBC). Levels of 0.4-2 ppm aluminum as AlCl(3) had a strong negative influence on labeling yield while 4-20 ppm of boron as KBO(2) and 50-250 ppm of silicon as Na(2)SiO(3) did not have a significant impact. Interesting interaction effects between the elements were observed, where particularly KBO(2) reduced the negative effect of AlCl(3) on labeling yield. It can be concluded that leachables of borosilicate glassware easily can influence nucleophilic substitution with n.c.a. [(18)F]F(-) and give variable yields.

A formulation development strategy for multivariate kinetic responses.

The purpose of this paper was to evaluate a multivariate strategy for handling time-dependent kinetic data during formulation development. Dissolution profiles were evaluated by the Weibull equation, multiple linear regression (MLR), principal component analysis (PCA), alone and in combination. In addition a soft independent modeling of class analogy (SIMCA) was performed. Employing a typical kinetic model for solid formulations (here Weibull) showed difficulties with the model adaptation, resulting in increased model standard deviation and thereby failure in identifying significant variables. In general, the selection of a kinetic model is crucial for finding the significant formulation variables. Describing the dissolution profile based on MLR models of individual time points described the dissolution rates as a function of formulation variables with good precision. Establishing prediction models made it easy to evaluate effects on the entire dissolution profile. The use of PCA/MLR (PCR) reduced the influence of noise from single measurements in a kinetic profile, since they develop statistical parameters representing the profile without being dependent on a physicochemically-modeled profile. The use of PCA reduced the eight time-point variables to two latent variables (principal components), simplifying the classification of formulations and new samples as well as avoiding unwanted effects of model non-linearities between the factors and responses (model error). The group membership of new samples was demonstrated by SIMCA.

Preparation of polymeric microcapsules: formulation studies.

Air-filled microcapsules were prepared by freeze-drying different oil-in-water emulsions containing biodegradable polyester as the wall-forming material. The aim of this work was to find an acceptable formulation with respect to the microcapsule suspension and the stability of the emulsion during the production process. The influence of various formulation parameters (concentrations of mannitol, polymer, and surfactant; pH; oil-in-water phase ratio) was investigated in a factorial design. The results were treated by ordinary least-square (OLS) regression and partial least-square regression (PLSR). In a previous work, air-filled microcapsules were successfully made using human serum albumin as the surfactant in the emulsion (1). In the present work, a new block copolymer based on poly(ethylene glycol) (PEG) was implemented as the surfactant to replace human serum albumin. It was found that the new block copolymer is a suitable replacement for human serum albumin. The concentration of the polymer in water and the concentration of the surfactant in the oil phase and the interaction between these variables had a significant influence on the stability of the emulsion at 60 degrees C. A surfactant concentration of approximately 2% (w/v) in water was necessary when the concentration of the wall-forming polymer was below 5% (w/v) in (-)-camphene. The concentration of the polymer in the oil phase influenced the yield, measured as the volume concentration of particles in suspension per milligram of polymer added and as acoustic effect per milligram of polymer. Low levels of polymer concentration in (-)-camphene (< 5% w/v) gave the highest yield. Excess polymer in the oil phase did not form microcapsules, but precipitated in the suspension or was included in the wall of the microcapsules. Addition of mannitol protected the microcapsules from being destroyed during freeze-drying and resulted in freeze-dried products with few cracks, little shrinkage, and higher suspension yield.

A chemometrics method for separation of size dependent and size independent attributes of microspheres for medical ultrasound imaging.

The size dependent and size independent contributions to the mechanical properties of poly(ethyleneglycol) microspheres with encapsulated air, made for medical ultrasound imaging, have been studied. A relation between the size of microspheres in a reference group and their acoustic attenuation efficacy was derived by partial least square regression. The developed model was used to estimate acoustic attenuation as a function of the measured size distribution for various preparations made during formulation and process studies. The ratio between the measured attenuation and model estimated attenuation was then used to evaluate variations in the mechanical properties of the polymer shell and the contribution of such variations to the acoustical properties of the substance. The statistical parameter was compared with results for the mechanical compressibility derived from a theoretical approach and the results from the two methods mutually confirmed each other. The statistical procedure outlined has been found applicable for studies of other particulate products with size dependent in vitro or in vivo properties.

Development of pectin matrix tablets for colonic delivery of model drug ropivacaine.

The objective of this work was to develop pectin-based matrix tablets for colonic delivery of the model drug ropivacaine, with the future perspective of radiolabelling the system by neutron activation technique for a gamma-scintigraphic study. The aim was to investigate some formulation factors that could reduce the release of the drug in the simulated gastric and intestinal fluids, increase the release in the simulated cecal fluid (with pectinolytic enzymes) and improve the poor compactibility of pectins. For dissolution studies, the flow-through apparatus with sequential dissolution liquids simulating the mouth-to-colon conditions was used. The effect of two pectin types, the incorporation of ethylcellulose as a dry matrix-additive and water or ethanol as granulation liquids were investigated in a study designed as a D-optimal mixture. Amidated pectin (Am.P) produced harder tablets than the calcium salt of pectin (Ca.P) and was more susceptible to enzymatic degradation. Addition of ethylcellulose increased the tablet strength and the dissolution rate. Furthermore, directly compressed Am.P tablets were produced by addition of coarse or micronised qualities of ethylcellulose. The latter improved the crushing strength markedly imposing a marginal release-reducing effect. Coating this formulation with Eudragit((R)) L 100 reduced the release in the simulated upper GI conditions without interference with the subsequent enzymatic activity.

An opportunistic stability strategy; simulation with real data.

A multivariate modelling procedure is proposed in order to identify factors influencing stability, to estimate shelf-life, to select new batches for further stability testing and to evaluate changes in new batches. A model developed by the proposed procedure predicts the degradation rate constant as a function of storage temperature, pH, concentration and volume. The predicted rate constants were compared with prospectively measured rate constants, primarily from new batches stored under stress conditions, which emphasised batch differences earlier than storage under normal conditions. Strong deviations from expected rate constants led to extended testing of the batches concerned. The new data were used to upgrade the multivariate model. The procedure proposed led to the formulation of an opportunistic stability strategy (OSSY). Of the 15 batches of injectable solutions, nine batches are proposed tested by using OSSY. This led to an approximately 75% reduction in analytical measurements. Hold samples are recommended for storage under several stability conditions for back up analysis. In general, a multivariate stability model should be based on scientific data obtained from early studies, such as preformulation and formulation studies to provide both a qualitative and quantitative understanding of the mechanisms involved.

A multivariate method to predict the water vapour diffusion rate through polypropylene packaging.

Semipermeable containers typically allow water to diffuse upon storage. The water diffusion rate of the widely distributed X-ray contrast agent Visipaque in polypropylene bottles and MR contrast agent Omniscan in polypropylene syringes has been evaluated. The goal was to develop a mathematical method for estimating the rate constant for water diffusion through the polypropylene wall as a function of several variables. The method presents an opportunity to measure the effect of the variables influencing product stability and thereby predicting the shelf-life at an early stage of the stability study. The effect of temperature, humidity, surface area, wall thickness, concentration of active ingredient and fill volume on the logarithmic rate constant for diffusion was estimated by partial least squares regression. The predictive ability of the cross-validated models was good (r = 0.99) for the two contrast agents. The models were used to predict shelf-life for relevant combinations of temperature and humidity, for the four defined climatic zones.

Acoustic properties of NC100100 and their relation with the microbubble size distribution.

RATIONALE AND OBJECTIVES: NC100100 is a contrast agent for medical imaging with ultrasonography consisting of stabilized gas microbubbles in an aqueous suspension. The objective of this article is to explore the acoustic properties of NC100100 and their relation with the microbubble size distribution. The results are used to motivate the choice of a suitable assay/dosage parameter for precise control of product efficacy. METHODS: The concentration and size distribution of microbubbles in > 50 preparations of NC100100 were determined by Coulter counting, and the acoustic attenuation and backscatter efficacy were determined for all samples. The in vivo efficacy of the product was investigated by harmonic imaging of the heart in a dog model. RESULTS: The results demonstrated that the attenuation and backscatter efficacy per microbubble volume vary strongly with size, showing distinct maxima with respect to microbubble diameter. Sizes for optimal attenuation per volume ranged from 2.6 to 5.8 microns, depending on ultrasound frequency. The contribution of the smaller end tail of the microbubble distribution was shown to be negligible. From the observed size dependency for the acoustic properties, the volume concentration of microbubbles was chosen as the assay/dosage parameter for NC100100. The accuracy of this parameter as a descriptor of product efficacy was demonstrated by precise, linear relations between volume, concentration, and attenuation/backscatter. In comparison, the correlation between the microbubble number and acoustic properties was not significant. Results from the in vivo study showed a precise, linear relation between injected microbubble volume and the observed in vivo efficacy. CONCLUSIONS: The acoustic properties of NC100100 are dependent on microbubble size. The observed batch-to-batch variance in the acoustic properties of the product may be fully explained by variation in concentration and size. Microbubble volume is a more precise predictor of in vitro/in vivo efficacy than microbubble number and consequently was chosen as the assay/dosage parameter for NC100100.

Relationship between size of injected microspheres and ultrasound imaging of heart by PLSR.

PURPOSE: To investigate the enhancement in ultrasound signal (US) in heart, for diagnostic purposes, as a function of size and number of injected air-filled microspheres by multivariate statistical methods. METHODS: The US enhancement in left ventricle was measured after injection of 31 suspensions of air-filled albumin microspheres divided on and injected in six dogs. The relationship between the size of microspheres between 1-38 microns and the US enhancement was explored by Pearson's product moment correlation analysis, ordinary least-squares regression, principal component regression (PCR) and partial least-squares regression (PLS). RESULTS: Relative advanced algorithms such as PCR and PLS were required to achieve accurate in vivo/in vitro correlation. The most effective microsphere sizes contributing to US enhancement in left ventricle in dogs were estimated to be in the 7-15 microns range. CONCLUSIONS: In general, the effective in vivo sizes are dependent on the type of formulation due to the surprisingly large active in vivo sizes found for the tested concept. PCR and PLS are suitable methods for in vivo/in vitro correlation, especially for covariated and noisy data.

Effect of microsphere size distribution on the ultrasonographic contrast efficacy of air-filled albumin microspheres in the left ventricle of dog hearts.

RATIONALE AND OBJECTIVES: The in vitro ultrasonographic contrast efficacy of air-filled albumin microspheres has been found to depend on the size distribution of microspheres. The objective of the current study was to empirically describe the relationship between the size distribution of injected air-filled albumin microspheres and the in vivo contrast efficacy after lung capillary filtration in a dog model. METHODS: Twenty different air-filled microspheres with large and well-defined differences in size distribution were prepared from nine different batches of Albunex (Molecular Biosystems Inc.) and subsequently characterized by Coulter counting. The in vivo ultrasonographic contrast enhancement of these preparations was investigated with a VingMed CFM750 in closed chest model in six mongrel dogs. The observed contrast efficacy, measured as gray-level enhancement in the left ventricle (LV), was correlated to the microsphere size distribution, using both univariate and multivariate approaches. RESULTS: The results demonstrated a significant contribution to LV contrast efficacy from microspheres larger than approximately 7 microm, and a lack of contribution from microspheres smaller than approximately 7 microm. Linear relationships were found between LV contrast efficacy, and both the number concentration of microspheres between 8 to 12 microm and the total microsphere volume concentration. No significant covariance between in vivo contrast efficacy and the number concentration between 1 to 38 microm or 4 to 10 microm was observed. The multivariate model showed a significant contribution to the in vivo gray-level enhancement from microspheres in the size range 7 to 15 microm, with optimal efficacy per microsphere at approximately 13 microm. CONCLUSIONS: Large microspheres (> 7 microm), which had been expected to be trapped in the lung capillary bed, contribute most of the observed ultrasound contrast in the LV of the heart.

Relationship between viscosity and determined injection pressure in angiography catheters for common roentgen contrast media.

The viscosity of 8 commercially available contrast media (CM) at 2 or 3 concentrations were measured as a function of concentration and temperature, using a rotational viscosmeter. Further on, by use of an automated injector, injection pressures were measured for 3 of the CM at various concentrations, temperatures, catheter lengths, catheter diameters and flow rates. The experiments were performed as fractional factorial designs. The correlation between the injection pressure and the viscosity was found to be log-linear, and an empiric equation was established for this relationship. The relative reduction of viscosity - and therby injection pressure - with increasing injection temperature, was largest for the most concentrated CM. Iodixanol and iotrolan, the 2 nonionic dimers investigated, demonstrated an increased viscosity compared to the nonionic monomers at equal concentrations. However, all CM investigated could be used with an acceptable injection pressure either by relatively small changes in catheter conditions or by adjustment of injection temperature closer to body temperature.