Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs.

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.