Suspensions nasal formulations

Suspensions may also be used to deliver nasal formulations, though only rarely, since a number of complicating factors (e.g., particle size and morphology) must be considered. Suspensions offer the advantage of increasing residence time in the nasal cavity, thus possibly augmenting nasal bioavailability. 

For nebulizer and other aqueous aerosol products that use suspension systems, excipients are used to influence particle physical and chemical stability (e.g., microcrystalline cellulose for nasal sprays). The suitability of the physicochemical properties of these critical excipients should be thoroughly investigated and documented (12). Far more excipients have been included in formulations designed for nasal administration (Table 4). 

Both the type of drug delivery system and the specific type of delivery device can affect drug absorption via the nasal route. The choice of delivery system depends mainly on the physiochemical properties of the drug, its desired site of action, and, more importantly, patient compliance and marketing aspects. The formulations most commonly used in nasal delivery are solutions, suspensions, gels, dry powders, and, most recently, nanoparticulate formulations. 

Many of the points raised in this section have been mentioned in the earlier sections on formulation and device. A Guidance for Industry document in draft form was issued by the FDA during 1999, Nasal Spray and Inhalation Solution, Suspension, and Spray Drug Products Chemistry, Manufacturing and Controls Documentation (FDA 1999). This document provides a plethora of information on issues the FDA will consider in submitted documentation supporting the approval of nasal products. There are over 1,600 lines in the document, and industry comments have been invited. Whilst the final document has yet to be issued, the draft is still an important reference. A brief review of the content of this draft document follows. 

Nasal drops and liquid nasal sprays are solutions, emulsions or suspensions intended for instillation or spraying into the nasal cavities. Nasal powders or nasal insufflation powders are intended for insufflation into the nasal cavity by means of a suitable device. The size of the particles are such as to localise their deposition in the nasal cavity. In nasal sticks and so-called inhalation ointments mostly volatile active substances are formulated in a fatty base. Nasal washes are generally aqueous iso-osmotic solutions intended to cleanse the nasal cavity. If they are intended for application on injured parts of the mucosa, or prior to a surgical operation, they have to be sterile. Nasal powders and nasal sticks are not very common in pharmacy practice. Therefore they are not discussed in this chapter. 

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