| By Paul Kippax at Malvern Instruments assesses the importance of droplet size analysis in nasal spray testing
While the advantages of nasal sprays for both systemic and locally acting drug delivery are widely understood, the challenge remains to develop products with the required performance. A typical nasal spray formulation consists of an active ingredient dissolved or suspended in an aqueous medium, and is supplied with a metered pump, manually actuated by the user to disperse the active into the nasal cavity. The properties of the formulation, the design of the delivery device and the actuation characteristics of the target user group all influence dispersion behaviour. Product performance is essentially a function of these three parameters.
The focus of this article is the measurement of the spray droplet size produced by nasal pump sprays, as this is a key parameter that has a direct impact on the deposition and subsequent absorption of APIs in the nasal cavity. FDA requirements for nasal spray testing, and in particular droplet size measurement, are reviewed in relation to understanding the dynamics of atomisation. Case studies showing measurements made using the technique of laser diffraction, (as recommended by the FDA for in vitro testing) are used to highlight the relevance of droplet size data when characterising delivery device performance and optimising formulation properties.
NASAL SPRAY TESTING
A successful nasal pump spray product produces a uniform, consistently atomised dose for optimal absorption in the nasal passages each time it is used. In its draft guidance document relating to ‘Bioequivalence (BE) and bioavailability (BA) studies for nasal sprays and nasal aerosols for local action,’ the FDA has outlined a series of tests which can be carried out to assess nasal spray product performance as part of a new drug application or abbreviated new drug application. The FDA guidance recognises the benefits of in vitro testing for assessing BE/BA, and the direct correlation between certain physical characteristics, such as droplet size and product performance. Laser diffraction is recommended as an appropriate technique for droplet size measurement. |
