ABSTRACT
Two basic approaches have been used to increase the nasal residence times of drugs, and correspondingly to decrease intrasubject variation. These are firstly to use viscosity enhancers, and secondly to use a “bioadhesive” formulation to reduce the clearance rate. Two classes of bioadhesives have been used; firstly polymers which interact with the nasal mucus, and secondly microspheres. A large number of such formulations have been studied and many of them increase the residence time of the formulation, and alter the pharmacokinetics of the drug, causing increased bioavailability or duration of action. It is difficult to assess the exact physical mechanism by which these formulations operate. Many of the so-called bioadhesive polymers also act as viscosity modifiers, and many of the microsphere formulations hydrate to form glue-like gels which will adhere to the nasal tissues even in the absence of a specific particle-mucus interaction. As a result it is almost impossible to separate the importance of these effects in vivo and the importance of specific ‘bioadhesive’ interactions is questionable.
