Nasal absorption in the rat: IV. Membrane activity of absorption enhancers

A novel permeation enhancer: N-succinyl chitosan on the intranasal absorption of isosorbide dinitrate in rats

The purpose of this paper is to study the potential of N-succinyl chitosan as a novel permeation enhancer for the intranasal absorption of isosorbide dinitrate (ISDN). A series of N-succinyl chitosan (NSCS) with different degree of succinylation (DS) and molecular weight were synthesized. An in situ nasal perfusion technique in rats was utilized to investigate the effect of NSCS substitution degree, NSCS molecular weight and concentration on the intranasal absorption of ISDN. The absorption enhancing effect of NSCS was compared with that of chitosan. It was found that all the NSCS investigated improved the intranasal absorption of ISDN remarkably. Better promoting effect was observed for 0.1% NSCS 50 (63) compared with 0.5% chitosan 50. In nasal ciliotoxicity test, both NSCS and chitosan investigated showed good safety profiles. Thereafter, in vivo studies of the selected formulations were carried out in rats and the pharmacokinetic parameters were calculated and compared with that of intravenous injection. Both in situ and in vivo studies demonstrated that NSCS is more effective than chitosan in promoting intranasal absorption of ISDN. Taking both absorption enhancing and safety reason into account, we suggest NSCS is a promising intranasal absorption enhancer.

Dry powder vaccines for mucosal administration: critical factors in manufacture and delivery

Dry powder vaccine formulations have proved effective for induction of systemic and mucosal immune responses. Here we review the use of dry vaccines for immunization in the respiratory tract. We discuss techniques for powder formulation, manufacture, characterization and delivery in addition to methods used for evaluation of stability and safety. We review the immunogenicity and protective efficacy of dry powder vaccines as compared to liquid vaccines delivered by mucosal or parenteral routes. Included is information on mucosal adjuvants and mucoadhesives that can be used to enhance nasal or pulmonary dry vaccines. Mucosal immunization with dry powder vaccines offers the potential to provide a needle-free and cold chain-independent vaccination strategy for the induction of protective immunity against either systemic or mucosal pathogens.

Comparison of different absorption enhancers on the intranasal absorption of isosorbide dinitrate in rats

The objective of this work was to study the influence of different absorption enhancers on the intranasal absorption of isosorbide dinitrate (ISDN). First of all, an in situ nasal perfusion technique in rats was used to investigate the effect of pH, concentration of drug solution and different absorption enhancers on the intranasal absorption of ISDN. The absorption enhancers investigated include hydroxypropyl-beta-cyclodextrin (HP-beta-CD), chitosans (CS) of different molecular weight, and poloxamer 188. All of them enhanced the intranasal absorption of ISDN remarkably. It was found that poloxamer 188 had better permeation enhancing effect than that of HP-beta-CD and CS of the same concentration. Thereafter, in vivo behaviors of the selected formulations were studied in rats and the pharmacokinetic parameters were calculated and compared with that of intravenous injection. Both in situ and in vivo studies demonstrated that poloxamer 188 played a key role in promoting intranasal absorption of ISDN. In nasal ciliotoxicity test, all the absorption enhancers investigated showed good safety profiles. Taking both enhancing effect and safety into account, we suggest poloxamer 188 is the most promising as an intranasal absorption enhancer.

Absorption enhancers for nasal drug delivery

This paper describes the basic concepts for the transmucosal delivery of drugs, and in particular the use of the nasal route for delivery of challenging drugs such as polar low-molecular-weight drugs and peptides and proteins. Strategies for the exploitation of absorption enhancers for the improvement of nasal delivery are discussed, including consideration of mechanisms of action and the correlation between toxic effect and absorption enhancement. Selected enhancer systems, such as cyclodextrins, phospholipids, bioadhesive powder systems and chitosan, are discussed in detail. Examples of the use of these enhancers in preclinical and clinical studies are given. Methods for assessing irritancy and damage to the nasal membrane from the use of absorption enhancers are also described. Finally, the mucosal use of absorption enhancers (chitosan) for the improved nasal delivery of vaccines is reported with reference to recent phase I/II clinical studies.

Intranasal insulin delivery and therapy

Intranasal insulin delivery has been widely investigated as an alternative to subcutaneous injection for the treatment of diabetes. The pharmacokinetic profile of intranasal insulin is similar to that obtained by intravenous injection and, in contrast to subcutaneous insulin delivery, bears close resemblance to the 'pulsatile' pattern of endogenous insulin secretion during meal-times. The literature suggests that intranasal insulin therapy has considerable potential for controlling post-prandial hyperglycaemia in the treatment of both IDDM and NIDDM. However, effective insulin absorption via the nasal route is unlikely without employing the help of absorption enhancers or promoters which are able to modulate nasal epithelial permeability to insulin and/or prolong the residence time of the drug formulation in the nasal cavity. This article discusses the structure and function of the nasal cavity, the barriers which prevent nasal insulin absorption and through the use of absorption enhancers or promoters methods by which these barriers may be overcome.

Absorption enhancers as tools to determine the route of nasal absorption of peptides

The nasal absorption of a series of peptides was studied in order to examine the relationship between extent of absorption and lipophilicity and absorption enhancers were used to probe the mechanism of peptide absorption. An in situ rat nasal perfusion technique was employed to assess the nasal absorption of a series of peptides, D-FGGGGG (D-FG5), D-FD-FGGGG (D-F2G4) and D-FD-FD-FGGG (D-F3G3), [D-ala2, D-leu5]enkephalin (YD-AGFD-L) and thyrotrophin releasing hormone (TRH). The enhancers sodium tauro-24,25 dihydrofusidate (STDHF), ethylene diamine tetraacetic acid (EDTA and dimethyl-beta-cyclodextrin (DMbetaCD) were utilized to improve and elucidate the mechanisms of peptide absorption. There was no significant relationship between extent of peptide absorption and lipophilicity as determined by C log P values. STDHF was a potent absorption enhancer but demonstrated overt toxicity. Conversely, EDTA did not demonstrate extensive toxicity but was found to be a poor absorption enhancer. DMbetaCD displayed some toxicity and was also found to inhibit the absorption of D-FG5,D-F2G4 and D-F3G3. This reduction is likely to be a result of the peptide/DMbetaCD complex formation. The peptides studied appear to be predominantly absorbed by a passive paracellular mechanism.