At Pierre Fabre Laboratories, supercritical fluid technology is being used to enhance the drug bioavailability of poorly soluble pharmaceutical actives. Florence Marciacq, Hubert Lochard and Bernard Freiss explain how
The use of high-throughput screening and similar techniques in drug discovery can provide new candidates that present both high molecular weight and low water solubility. Researchers are then faced with finding new formulation techniques that enable, and increase, the bioavailability of these active pharmaceutical ingredients (APIs).
Among the different technologies available, supercritical fluids technology has already been used to enhance bioavailability of active substances, either by increasing the solubilisation kinetic or by modifying the apparent solubility of the molecule.
The Supercritical Fluids Division of Pierre Fabre Laboratories has been involved in supercritical fluids for nine years. Most of its work has been carried out on supercritical CO2.
A supercritical fluid is a fluid used at temperature and pressure above its critical values. Such fluids have a density similar to liquids but are gas-like in terms of their viscosity. As a result, material and heat transfers are fast and efficient. The properties of this type of fluid can be easily modified by slightly "tuning" the pressure or temperature. Figure 1 shows the isodensity curves in a pressure/temperature diagram.
Carbon dioxide is often used as a supercritical liquid because it is a non-toxic, cheap, easily available solvent and its critical point is easily reached (31°C, 74 bar). For these reasons supercritical carbon dioxide is considered a "green" solvent. Another important
feature is that at room conditions, carbon dioxide is a gas. This means that once the process is complete, simple depressurisation enables the powder to be obtained without residual solvent.
The family of oligosaccharides known as cyclodextrins are commonly used to form inclusion complexes with hydrophobic organic molecules to enhance API apparent solubility.
Because the outside surface of these molecules is hydrophilic and the inside surface hydrophobic, they are able to capture, fully or partially, in their cavity large organic molecules via non-covalent bonds. Thus, the physical and chemical properties of the captured molecules may be modified and, in particular, the physical stability and aqueous solubility can be improved.
Several techniques have been used to prepare inclusion complexes, such as kneading, freeze-drying, grinding, co-precipitation and melting. However, the poor aqueous solubility of many non-polar drugs means the high energy and process costs of these techniques make them less favourable than supercritical CO2 complexation.
Pierre Fabre Medicament has developed an extensive expertise in supercritical fluid technology, focused on the development of new tools for the formulation of active ingredients. Among the processes developed is Formulplex, a patented complexation process involving cyclodextrin in a powder form, used to improve the bioavailability of poorly soluble drugs.
The physical properties of supercritical fluids (density, viscosity, diffusion constant, mass transfer) make the thermodynamic constants and reaction kinetics of the complexation observed different from that of other complexation processes. Therefore complexes obtained in supercritical CO2 present structure characteristics that are different from those obtained using other techniques. An interesting property is that in many cases, the interactions between the active ingredient and the cyclodextrins are more efficient, resulting in a higher apparent solubility of the complex obtained.
Another feature is that, in some cases, a complexation that is not obtained by conventional methods occurs in a supercritical medium. The API/cyclodextrin complexation is an equilibrium process that is dependent on the medium. The process that leads to the inclusion complex is regarded as environmentally friendly, using only carbon dioxide, a catalyst and water.
In certain cases, an enhancement of the stability of APIs in aqueous media has been observed. Furthermore, this technology does not require any mechanical mixing. This is an important issue, because the avoidance of local over-heating of the material prevents any potential degradation of temperature-sensitive molecules.
Formulplex 1 is a single-step complexation process that requires supercritical carbon dioxide to be added to a mixture of the API, the cyclodextrin and a catalyst in water. The operating parameters are: the raw material ratios, pressure, temperature and reaction time. At the end of the step, depressurisation produces the complex in solid form without any residual solvent. This simple and reproducible reaction allows a rapid and reliable scale-up.
The results presented in table 1 underline the effectiveness of the Formulplex technology for various types of drugs. It provides, for example, aqueous solubility after 15 minutes in a 37°C aqueous solution. The cyclodextrins used for the trials are a, b, g, hydroxypropyl-b and methyl-b-cyclodextrins.
The water-solubility of the complexes obtained using supercritical CO2 are presented for comparison with that of the complex obtained in water. A significant increase in solubility is observed through the implementation of Formuplex 1. These solubility results are usually predictive of the bioavailability of the complexed active ingredient.
The complexation of a non-steroidal anti-inflammatory drug (NSAID), ibuprofen, is an interesting case study. Different formulations were tested in animals in order to compare ibuprofen processed with Formulplex and ibuprofen formulated conventionally using the same excipients. Pre-clinical tests were used to compare it with marketed ibuprofen.
For the Phase I clinical study, several 20kg batches were produced in Pierre Fabre Medicament's cGMP pilot scale installation. A comparative pharmacokinetic study was performed after oral administration in rats. The levels of ibuprofen in the plasma were measured and the maximal concentration (Cmax) and Area Under the Curve (AUC) were plotted for the different formulations (see figure 3).
Stability and clinical studies in 36 healthy volunteers have been realised. The results for formulations produced using the Formulplex complex versus commercial tablets of ibuprofen are given in figure 4.
The Formulplex ibuprofen presents a maximal concentration that is higher than marketed Nureflex, and the Cmax is also attained more rapidly with the Formulplex complex.
Within our previous investigations, the company developed a three-step process called Formulplex 3 (figure 5). The three steps are co-crystallisation, complexation and stripping. The first step enables the formation of a homogeneous and fine mixture of cyclodextrins and active ingredient that is favourable for the complexation that occurs in the second step.
The aim of the final stripping is to remove the traces of organic solvent used in the co-crystallisation step via a continuous flow of supercritical CO2. This process is less simple to develop but produces better results in terms of solubility and bioavailability.
Some published studies on the API Eflucimibe (developed by Pierre Fabre Laboratories) have shown that Formulplex 3 allows a dramatic increase in oral bioavailability of the drug. Figure 6 shows in vivo results obtained with Eflucimibe and g-cyclodextrins treated by
Formulplex 3 compared with other drug delivery technologies, used in a pre-clinical study on dogs (Biorise: solid dispersion; Nanocrystal: nanopowders formulation).
The equipment required to develop Formulplex processes, to perform the scale-up and to realise the first commercial batches are produced at the Supercritical Fluids (SFC) Unit of Pierre Fabre Medicament, Gaillac (France). The Supercritical
Fluids Division conforms with all the requirements of ICHQ7A, cGMP and BPF (Bonnes Pratiques de Fabrication).
The SCF development area can handle powder weights ranging from a few grams to hundreds of grams for development phases. The equipment set up is flexibile and includes:
- Non-Stirred autoclave 250 mL (x2)
- Stirred autoclave 500 mL
- Stirred Autoclave 2L
- Stirred Autoclave 5L
- Pumps from 3kg/h up to 50kg/h.
The SCF development area is divided into four zones: circulation - for the technicians and raw materials and final product storage; non-cytotoxic powder; cytotoxic powder; and utilities.
The production area has been designed for manufacture of Phase I, II and III clinical study batches as well as commercial batches. This area is also divided into zones for production (including powder handling facilities); storage; sampling and weighing; and utilities.
The production area is composed of a CO2 pump (500 kg/h), and a 10L and 50L stirred autoclave. This equipment allows the manufacture of batches from few kilograms up to 30kg, which is largely sufficient to cover Phase I, II, and III clinical studies needs. The annual production capacity (with two shifts) is around 20 tons.
The difficulties encountered in the potential scale-up of the nano-crystallisation process have been overcome through Pierre Fabre's investigations into cyclodextrin complexation of poorly water-soluble APIs in a supercritical medium.
Through complexation of a poorly water-soluble API with a cyclodextrin, it is possible to enhance API solubility. A non-water-soluble API can be complexed, resulting in an increase in water solubility in excess of 300-fold. More recent trials have led to some higher improvements.
In terms of bioavailability enhancement, Formulplex supercritical CO2 technology shows many advantages over standard methods of complex-ation. In some cases, stabilisation of the API has also been observed. The cost and reaction time are dramatically reduced and, in some cases, complex-ations not observed in classical methods, occur in a supercritical medium. Complexation can also increase patent protection by creating a new final dosage form or by the use of Pierre Fabre's patented technology, leading to product life cycle expansion.
Innovation Award winner
Pierre Fabre Medicament was one of the winning entries
in this year's Innovation Awards at CPhI in Frankfurt.
The company won Silver for its innovative application
of complexation process Formulplex.