How does aseptic spray drying compare with other aseptic technologies?
Liquid formulations are the preferred drug delivery solution for a wide range of sterile pharmaceuticals because they are
well accepted with low-cost processes and offer relatively good convenience for the user. Product stability and cold chain
challenges, however, make dry formulations attractive solutions as well.
Today, most dry formulations are produced by lyophilisation, which is a long-established process for producing stable powders,
but has a high-total cost for installation and operation. It is also a lengthy batch process (often up to 48 h to process
a batch) that carries the risk of losing a whole batch if, for any reason, process conditions are not maintained throughout
the cycle. To reduce the risk of losing a batch, there should be backup systems in place, but this increases both installation
and operation costs.
Compared with lyophilisation, spray drying is generally more flexible in terms of product and powder characteristics and processing
time. However, the yields in spray drying processes are typically around 98–99% rather than 100%, which is the theoretical
level that can be obtained in a lyophiliser (under the condition that all batches are successfully processed and that all
vials come out in perfect shape). This can make a significant difference on expensive products. Additionally, because spray
drying is very flexible in terms of product and powder characteristics, there are possibilities for making the wrong powder
characteristics. In many cases, this is apparent only as poor yield. For small development batches produced on small laboratory
or pilot spray dryers (frequently with non-optimised process conditions and equipment), the yield may be significantly less
than what can be achieved on full batches and with optimised process conditions. This is important to keep in mind in order
to avoid rejecting the spray drying technology due to wrong selection of process conditions or equipment.
Comparing the costs of the two technologies, spray drying is in general more economical in terms of installation and operation
compared with lyophilisation. For instance, the evaporative capacity of a normal-sized pharmaceutical spray dryer can match
that of 5–7 large lyophilisers. Full operational and life cycle costs must also be considered when comparing the two technologies.
In many cases, however, spray drying and lyophilisation are complementary technologies. For small batches of difficult-to-dry
powders to be supplied in vials, lyophilisation has an advantage, whereas spray drying has an advantage if free-flowing powders
are required, and for productions in large quantities.
Henrik Schwartzbach Senior Process Technologist at GEA Niro