In silico and in vitro models in pharmacokinetic studies

2011 - 2012One of the aims of the thesis was to design and realize an in vitro device able to reproduce the gastrointestinal behavior. To reproduce the temperature and pH history an USP apparatus II coupled with a control system was used. The temperature was kept constant using the USP apparatus, a pH probe was inserted in the dissolution medium to measure the pH. The measured pH was compared (by a software) with a set point. Proportionally at the mean error, a quantity of an acidic or basic solution was inserted, by pumps, in the dissolution medium adjusting the pH at the desired value. Using the real pH history of the gastrointestinal tract, which provide a decrease in the pH value from 4.8 to about 2.0 during the first two hours of dissolution, and then an increase to 6.8, the release pattern from tablets was evaluated. The release patterns of these tablets obtained with the new device were compared with those obtained using the conventional method (which provides a pH 1 during the first two hours of dissolution, and then the neutralization at pH 6.8) and it was found that the drug released during the first two hours was higher in the case in which the real pH history was reproduced. This is due to the fact that the higher pH in the first stage damages the coating of the tablet. Once the chemical and thermal conditions were reproduced, the reproduction of the transport across the intestinal membrane was faced. An high throughput device which is able to reproduce continuously the exchange between the compartments has been necessary. The USP apparatus was equipped with a device composed by an hollow filter (which simulate the intestinal wall) and two pumps for the fluids simulating the intestinal content and the circulatory system surrounding the gastrointestinal tract content. The fluids enter in contact in the filter and the fluid rich in drug content (that simulates the intestinal content) gives the drug to the fluid poor in drug (simulating the blood content). The release patterns obtained by the use of this device were studied and compared with those obtained following the conventional dissolution method. Moreover these release patterns obtained using the real pH evolution were coupled with the effect of mass exchange and compared with those obtained using the conventional methods. The results showed that the effect of the real history of pH is higher in the first stage of dissolution, than the effect of the mass exchange is dominant. The reproduction of the mechanical history of the stomach is than faced. The peristaltic waves were reproduced using a lattice bag (elastic and compressible) connected to a camshaft which, with its rotation ensured the contraction of the bag. The bag was shrunk by connectors and the right position was ensured by guides. Changing the rotation speed of the shaft, the frequency of the contractions could be adjusted. The release pattern of a commercial tablet in the new device was evaluated and compared with the conventional one. The results showed that the non-perfect mixing of the stomach was satisfactory reproduced and this lead to a release pattern completely different. Moreover, the effect of the frequency of the contractions on the release pattern was evaluated. Second, but not secondary, aim of the thesis was to develop an in silico model (physiologically based) which is able to simulate the plasma concentration of drugs. The model is composed by seven compartments, which simulate the human organ, tissue, or a group of them. The compartments are interconnected between them and seven differential equations (with their initial conditions) describe their behavior. Once the parameter are obtained (by fitting or in literature), using an in vitro release pattern, the model is able to simulate the concentrations in all the compartments, including the plasma compartment. The plasma concentration are simulated both in the case in which the new release pattern (with the real pH history) is used as input, and the case in which the conventional one is used. The results show that in the real case the plasma concentration is very different both in value and in shape than the expected. The model then was used to simulate the fate of several molecules simultaneously in the human body (i.e. if a racemic mixture is administered or if the drug is metabolized to another molecule). The system of differential equations is expanded to describe the fate of each molecule. Then, the physiological parameters, such as gender and age, were integrated in the model; in this way, the dependence of the model parameter on the physiological parameter was evaluated. Finally, the gastrointestinal concentration simulated with the in silico model was successfully compared with the drug concentration measured with the in vitro model. It could be concluded that the combined approach which uses the in vitro and the in silico models is a powerful tool in the pharmacokinetic studies. [edited by Author]XI n.s

Controlled drug release from hydrogel-based matrices: Experiments and modeling

Controlled release by oral administration is mainly achieved by pharmaceuticals based on hydrogels. Once swallowed, a matrix made of hydrogels experiences water up-take, swelling, drug dissolution and diffusion, polymer erosion. The detailed understanding and quantification of such a complex behavior is a mandatory prerequisite to the design of novel pharmaceuticals for controlled oral delivery. In this work, the behavior of hydrogel-based matrices has been investigated by means of several experimental techniques previously pointed out (gravimetric, and based on texture analysis); and then all the observed features were mathematically described using a physical model, defined and recently improved by our research group (based on balance equations, rate equations and swelling predictions). The agreement between the huge set of experimental data and the detailed calculations by the model is good, confirming the validity of both the experimental and the theoretical approaches

Swellable Hydrogel-based Systems for Controlled Drug Delivery

The controlled delivery of drugs can be effectively obtained using systems based on hydrogels. Tablets, to be orally administered, represent the simplest and the most traditional dosage systems based on hydrogel. Their formulation and preparation require to mix and to compress, in proper ratios, various excipients, including a swellable polymer and a drug. Carriers for controlled release systems are usually cross-linked polymers able to form hydrogels that show peculiar release mechanisms, where both diffusion and tablet swelling play important roles

Intensification of biopolymeric microparticles production by ultrasonic assisted atomization

In this work ultrasonic atomization process is applied to produce biopolymer microparticles with potential applications in pharmaceutical and nutraceutical fields. Natural polymer (alginate)/water solution is atomized by ultrasonic assisted process and the droplets spray is reticulated using a solution of copper sulfate, where the Cu2+ ions cause the formation of a network structure (hard porous gel). Several operating parameters (solution concentration, flow rate, atomization power) are changed to study their effects on the produced microparticles. Literature correlations able to predict the features of the droplets as functions of process parameters are optimized using a statistical approach. Furthermore, the energy requirement for the drops production is compared with the energy required by traditional techniques to evaluate the intensification effect of the ultrasonic on the atomization process. doi:10.1016/j.cep.2009.08.00

Microencapsulation effectiveness of small active molecules in biopolymer by ultrasonic atomization technique

A method to produce biopolymeric (alginate) microparticles by ultrasonic assisted atomization, previously developed, has been applied to the production of microparticles loaded with a small active molecule (theophylline). Fine loaded alginate droplets have been cross-linked with divalent ions to produce microparticles. Once produced, the particles have been separated by centrifugation or filtration and then they have been dried. Drug release has been evaluated by dissolution tests, dissolving the dried particles in acidic solution at pH 1 for a given time and then at pH 7 to simulate the stomach and intestinal environment, respectively. The encapsulation efficiency and the drug loading have been investigated and the operating conditions have been changed to clarify the role of the transport phenomena on the overall process. To increase the drug loading, shorter separation time and better network’s structure were identified as the key operating parameters to allow the process to gain interest from a practical point of view

An Engineering Point of View on the Use of the Hydrogels for Pharmaceutical and Biomedical Applications

In this chapter, the modern uses of hydrogels in pharmaceutical and biomedical applications are revised following an engineering point of view, i.e. focusing the attention on material properties and process conditions. The chapter discusses the applications following the increase in scale‐size. First, the nanoscale systems, i.e. hydrogel nanoparticles (HNPs), are analysed in terms of preparative approaches (polymerization methods and uses of preformed polymers) and with a brief mention of the future trends in the field. Secondly, systems based on hydrogel microparticles (HMPs) are examined following the same scheme (polymerization methods, uses of preformed polymers, a mention of novel and future trends). Thirdly, and last but not the least, the hydrogel‐based drug delivery systems (macroscopic HB‐DDSs) are presented, focusing in particular on tablets made of hydrogels, discussing the characterization methods and on the modelling approaches used to describe their behaviour. Other macroscopic systems are also discussed in brief. Even if the vastness of the field makes its discussion impossible in a single chapter, the presented material can be a good starting point to study the uses of hydrogels in pharmaceutical and biomedical sciences

Optimization of Chelates Production Process for Agricultural Administration of Inorganic Micronutrients

The iron chlorosis is one of the most diffused plant disease, which affects their growth and reduces the yield of harvests. This disease is caused by the iron deficiency and it is highlighted by the progressive yellowing of plants due to the reduction of chlorophyll production. The most efficient and diffused therapy against the iron chlorosis is the use of chelating agents and, among them, the o,o-EDDHA/Fe3+, the most stable isomer of EDDHA, is the most used due to its capacity to guarantee a prolonged treatment. The aim of this work is to develop a production process environment friendly, based on the recovering and recycling of organic solvents to minimize the waste produced. The feed organic solvents ratio has been varied evaluating the synthesis yield and the percentage of o,o-EDDHA/Fe3+ produced to identify the best feeding conditions. Several products have been then tested on lettuce plants to determine their usability

Designing in-vitro systems to simulate the in-vivo permeability of drugs

In this work an engineering approach, consisting in an experimental procedure and a model to derive the data, was presented and applied to improve the testing methods of pharmaceuticals. The permeability of several active molecules have been evaluated across a synthetic membrane. The permeability of these drugs measured through the artificial membrane were successfully correlated to their in-vivo permeability. The relationship with in-vivo permeability was derived, and then a rule to design systems to simulate the intestinal absorption was proposed to reduce the need for expensive and ethical problematic in-vivo measurement