Excipient fine particle fraction

Another reason for using excipient carrier is to improve the availability of fine drug particles in the aerosol cloud. Surface texture of excipients appears to play a prominent role. The fine particle fraction of... 

Besides surface texture, excipient particle size also plays an important role in the fine particle generation as shown by budesonide, where the highest fine particle fraction was obtained with small-sized (<32pm) lactose as the carrier. Additionally, fine particle excipients such as fine lactose or polyethylene glycol were reported to improve the performance of carrier-based protein dry powder aerosols.However, there are some cases where carriers improved total powder emission but reduced the percent of active powders in the aerosol. To be useful carriers, the excipients must be physically stable. The important physicochemical characteristics for drug carrier selection are discussed in Ref.t f... 

The most important incompatibility in capsules is the adsorption of active substances to excipients and vice versa. Sparingly water-soluble active substances may adsorb to non-water soluble excipients such as microcrystalline cellulose (diluent). On the other hand, the very fine glidant, colloidal anhydrous silica, can adsorb onto active substance particles. Especially for low dosed active substances, relatively large fractions may adsorb or be adsorbed. Such adsorption may delay the dissolution of the active substance, resulting in a delayed or incomplete release of the substance. This may lead to a reduced pharmaceutical availability and ultimately a lower therapeutic activity. Substances known to adsorb to microcrystalline cellulose are ethinylestradiol and dexamethasone [24]. 

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