Protein and Peptide Delivery through Respiratory Pathway - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 445

and actuator assembly. Sprays are cleared more slowly because deposition is local in
the anterior part of the cavity.
9.5.3.2.3.3 Nasal Emulsions, Microemulsions, and Nanoemulsions Viscosity of
nasal emulsions is generally an advantage for local application. The physical stability
of emulsion formulations and specific delivery are the main issues. A mucoadhesive
microemulsion will provide longer residence time in the nasal mucosa, indicating
rapid and complete absorption of drugs. Misra et al. have reported intranasal admin-
istration of mucoadhesive microemulsions for the effective management of various
brain-associated disorders [111,112] .
9.5.3.2.4 Semisolid Dosage Forms
Semi-solid systems include gels, ointments and pH dependent liquid systems. pH
dependent liquid systems contain polymers that gel at a particular pH are preferred
for designing the nasal drug delivery systems.
9.5.3.2.4.1 Nasal Gels Reduced anterior leakage of the formulation, reduced postna-
sal dripping due to high viscosity, reduced irritation by using soothing/emollient excipi-
ents, and target delivery to mucosa for better absorption are the various advantages of a
nasal gel. A vitamin B 12 and apomorphine gel has been successfully employed to achieve
desired therapeutic concentrations by nasal administration [113] . Thermoreversible gels
employing temperature-sensitive polymers have also been reported [114] .
9.5.3.2.5 Solid Dosage Forms
Solid dosage forms are more suitable for pulmonary drug delivery and similar appli-
cations because they cover the vasculature within the epithelium of nasal mucosa.
9.5.3.2.5.1 Nasal Powders Nasal powders may be advantageous if liquid dos-
age forms cannot be developed because of their lack of drug stability. The absence
of preservatives and superior stability of the formulations are other advantages, and
local application of the drug is yet another, but nasal mucosa irritation and metered-
dose delivery are some of the challenges for formulation scientists.
9.5.3.2.6 Novel Formulation Approaches for Intranasal Drug Delivery
9.5.3.2.6.1 Microspheres Microspheres, including mucoadhesive microspheres,
are specialized systems becoming increasingly popular for designing nasal products.
Microspheres may provide more prolonged contact with the nasal mucosa, which
enhances rate and extent of drug absorption [115] . Microspheres for intranasal appli-
cations are usually prepared using biocompatible materials, such as starch, albumin,
dextran, and gelatin [33,77] . However, their toxicity/irritancy on the nasal mucosa
due to the presence of a variety of polymers/excipients used in the preparation of
microspheres must be critically evaluated.
9.5.3.2.6.2 Nanoparticles Nanoparticles may allow transnasal drug delivery
to the brain, due to their small diameter, and are transported transcellularly via the
various endocytic pathways through the olfactory neurones. Targeted nose-to-brain
drug delivery is achieved by surface modification of the nanoparticles. Polymeric