Spray Drying Solid Dosage Forms

Pharmaceutical spray drying is a very fast method of drying because of the very large surface area created by the atomization of the liquid feed. As a consequence, high heat transfer coefficients are generated and the fast stabilisation of the feed at moderate temperatures makes this method very attractive for heat-sensitive materials.

From Formulation to Production

Spray drying provides unprecedented particle control and allows previously unattainable delivery methods and molecular characteristics. These advantages allow previously unattainable delivery methods and molecular characteristics to be explored.

The spray dryer is a suspended particle dryer. Drying particles while suspended requires drying to be very fast and droplet trajectories must also be kept away from the drying chamber wall for as long as possible. Fast drying is achieved by effective and uniform atomization of the liquid, which creates a very large surface area, and by ensuring effective mixing of the droplets with the drying gas.

Fast, Reproducible and Versatile

By selecting the appropriate plant design and operating conditions it is possible, in a single process step, to produce a free-flowing powder comprising either single particles or controlled agglomerates for filling syringes, vials or implants. Spray drying is a lenient drying process that can be adjusted for a range of process conditions, including the drying of heat-sensitive materials. Being a highly reproducible process, spray drying can be scaled up to nearly any production size. Although spray drying and freeze drying are supplementary technologies, spray drying is generally more flexible, efficient and economical.

Spray Drying as an Alternative to Granulation

Fluidized spray drying (FSD) - Produces granules from a liquid in a one-step process. One option is to produce the active in the primary production as granules, so that it only requires blending with excipients suitable for direct compression for secondary processing. This can only be done with actives that are tacky (in a wet state) otherwise the addition of a binder is necessary. Another possible use of FSD technology is to mix all the ingredients into a solution or suspension and to produce granules in a one-step operation. 

During the FSD process, the liquid feed is atomized at the top of the tower in a co-current mode. After the liquid is evaporated, the particles generated leave the drying chamber together with the exhaust air. These particles are then separated in a cyclone or filter and reintroduced into the drying chamber where they come into contact with wet droplets and form agglomerates. 

After these agglomerates have reached a certain weight they cannot leave via the top of the tower with the exhaust air, but fall down into the integrated fluid bed at the bottom of the drying chamber. Here they are dried and cooled before being discharged. However, this type of equipment is difficult to clean, particularly the external pipe work, when changing to another product. Systems have, therefore, been developed where the external pipe work does not come into contact with the product.

Bioavailability

Whether reformulating an existing compound or working with an NCE, the ability to understand and manipulate pharmacokinetic behaviour is key. For poorly soluble compounds, spray drying presents an alternative approach to oral dosage form development. This readily scaled-up and efficient process results in stable crystalline constructs that increase API bioavailability by increasing the solubility of the active ingredient.

Modified Release

Spray drying is much more than a simple drying technique. By carefully manipulating drying conditions and choice of excipient, the technology can also be used to delay/modify the release of drugs. This aspect of spray drying is often referred to as microencapsulation and has a number of applications, including

  • taste masking 
  • modified release (in the GI tract)
  • protecting the drug from the environment.

Microencapsulation can be undertaken with the API either in solution or as a micro/nanosuspension in solution containing the encapsulation agent. The physical properties and the type of polymer used to microencapsulate the drug in question will depend on 

  • site of delivery
  • physical properties of drug (such as solubility)
  • required drug load. 

By selecting specific polymers and grades (or mixtures thereof), it is possible to modify the release of drugs to enable improved efficacy as well as the potential to reduced side-effects.

Spray drying is a technique preferred by a growing number of pharmaceutical manufacturers to produce better drugs. This ultrafast and gentle drying technology offers unique ways to define particle characteristics. One advantage of spray drying is the remarkable versatility of the technology, evident when analysing the multiple applications and the wide range of products that can be obtained. From very fine particles for pulmonary delivery to big agglomerated powders for oral dosages, from amorphous to crystalline products and the potential for one-step formulations, spray drying offers multiple opportunities that no other single drying technology can claim.

GEA has developed a dedicated series of pharmaceutical spray dryers. The PHARMASD™ (PSD) dryers have been designed using standard modules that incorporate all the features required for cGMP production in the drug manufacturing environment. Available in a range of sizes (1–7), PSD dryers offer capacity ranges from 80 to 4000 kg/h of drying process gas.

GEA also offers a range of spray dryers designed specifically for R&D, product development and small volume production. A pioneer in all aspects of spray drying with more than 10,000 contracted and installed plants worldwide, we can help you to choose the most suitable equipment, assessing each project on its individual needs and tailor the process and the spray dryer to match your specific requirements.