The pharmaceutical industry addresses a number of demands on novel respirable particulates, which from a process technology perspective can be broadly categorized into the areas of: performance (e.g. total/local lung deposition, immediate versus controlled release), processing (e.g. achieve flow properties) and stability (e.g. physical/chemical stability and activity).
A new trend in pulmonary drug delivery is to move from the liquid or pressurised formulations to dry powder inhalation formulations. This, in part, is due to the advantages of dry powder systems, including breath-actuated inhalation, limited coordination requirements, no propellant requirement and short treatment time.
Spray drying is a simple, rapid, reproducible, economic and easy to scale-up production process that has been intensively studied for pharmaceuticals and excipients for pulmonary drug delivery in dry powder inhalation systems. It has the potential to generate highly dispersible powders for inhalation in the range from 1 to 5 µm size with a particle morphology that can more easily be influenced compared to for example jet milling.
This study reports a review, regarding research work on particles for inhalation that have been published in the RDD proceedings database, using laboratory scale Büchi Mini Spray Dryer models B-190, B-191 and B-290. Please download the review in PDF format here.
The Mini Spray Dryer B-290 from Büchi Labortechnik AG is a laboratory scale instrument to perform spray drying processes down to 30 mL batch volume and up to 1 litre of water or organic solvent per hour. Thanks to the glassware, the complete drying process from the two-fluid nozzle down to the powder collection vessel is visible. Fine particles are produced because of the short residence time in such a compact spray dryer.
The residence time of the drying air within the spray chamber is about 1.5 seconds. The powder collection is provided by a glass-made cyclone separator, which is internally coated with a thin nanosize antistatic film to reduce powder adhesion to the glass wall. The separation works by centrifugal forces by virtue of inertia of the solid particles.
Spray drying is a very useful technique to produce inhalable dry powders with predetermined specifications. There is significant research activity in dry powder aerosol formulation to treat several diseases including asthma, tuberculosis, diabetes and bacterial infection in the lung.
Spray drying offers great potential to these applications because of the easy achievement of the accepted optimum size range for locally acting inhaled drug particles (about 0.5 – 3.3 µm which represents deposition in the lung alveoli). The key benefits of this technology are the possibilities to control the size and morphology of the particles under a relatively gentle processing method.
Indeed, this method has been proven for the preparation of heat-sensitive materials such as protein based drugs. While the traditional bench-top spray dryers have been shown capable tools for the laboratory aim generation of respiratory sized particles, the area of process technology is ever-evolving.
The Nano Spray Dryer B-90 offers new possibilities in the field of laboratory scale spray drying and eliminates some weak points of traditional spray dryers; including increased recovery (up to 90%), small quantity production (100 mg amounts) and highly definable particle size ranges (300 nm – 5 µm) .