Home and dry – improving nasal sprays

Regular users of nasal sprays, such as myself, will be all too aware of some of their more irritating side effects which can include nose bleeds, and a rather unpleasant after taste. These can be caused by some of the excpients used to improve product stability and promote drug absorption.

Well, it turns out that dry nasal sprays could be the answer.

Echoing the growing use of dry powder inhalers (DPIs), interest in dry powder drug delivery via the nose is a hot topic in inhaled drug delivery circles. This is technology that potentially has much to recommend it, beyond greater patient acceptance.

Why dry?

One issue that a switch to dry delivery can address is the need for stability in the stored dose. Through the use of capsules and other sealing technolgoies, a dry powder environment can be made less hospitable to microbes than one containing moisture. For example, vaccine delivery using dry nasal sprays,  could avoid the cold supply chains required for the solution/suspension based alternatives, thereby significantly cutting cost. Studies into improving the effectiveness of nasal spray vaccines delivery are therefore underway. At the recent Drug Delivery to the Lungs (DDL) conference in Edinburgh, Bend Research presented an excellent paper showing how novel, spray-dried, virus-like particles (VLPs) can be used to enhance the immune response observed when delivering vaccines via the nose.

Those, like me, familiar with the influence of particle size on deposition within the body will also readily appreciate other possible advantage of dry nasal sprays. With nasal delivery, droplets or particles smaller than 10 microns may represent a problem because they can be drawn through the nose and into the lungs. The risk of this occuring is something which needs to be assessed during product development, as many of the excipients available for use in nasal sprays are not licenced for formualtions targeting the lung. So, size does really matter, as was pointed out in Bend Research’s DDL paper. Engineering a liquid atomisation system which can atomise a formulation effectively is relatively straightforward, as the technology to do this has been around for many years. However, doing this without producing a proportion of fine droplets can be difficult.  In the case of dry powder formualtions, very fine particle can be removed by design during manufacture of a product. Delivery itself is very unlikely to generate more fines, unless its extremely energetic or the particles are very fragile. Of course, the challenging of achieving reproducable dispersion of the dry powder dose remains!

Testing times

At an RDD-Europe workshop last year, Dr Julie Suman, President of NextBreath LLC, and I took on the challenge of looking at dry nasal sprays, with the goal of understanding whether the analytical methods applied to conventional liquid formations could be used to understand device performance. We concluded that laser diffraction remains useful in both instances, but that analysis of dry powder formulations does require some extra information relating to the particle size of the API within the formualtion. This challenge is similar to that faced by DPI developers, where impaction-based particle sizing methods, coupled with HPLC analysis, provide one way of obtaining API-specific size distributions. Products such as the Morphologi G3-ID which also has potential here.

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