A Comparative Study Between the Strength and Duration of Mucosa-Adhesion of Transbuccal Carbomer Based Aqueous Gels

Mucosa-adhesive gels can be used as a useful mean of delivering drugs to or via mucosal membranes, and in particular buccal mucosa. Carbomers are among the best mucosa-adhesive materials known. The aim of this study was to compare the results obtained from the mucosa-adhesive strength of aqueous gels containing Carbomers, either alone or in combination, to the data obtained from assessing the duration of mucosa-adhesion of these gels. Based on initial studies, a total Carbomer concentration of 2.0%w/v forms the most desirable gel. Furthermore, it was found that gels containing a combination of Carbomers 934P (C934), 971P (C971) and 974P (C974) form clear and transparent gels with good spreadability. Next, using these Carbomers, gels containing either one, two or all three Carbomers with a total polymer concentration of 2.0%w/v were prepared and tested for their mucosa-adhesive strength to rat small intestine (as model mucosa) in pH6.8 isotonic phosphate buffer at 37 ?C. It was found that the presence of more than 0.4%w/v C971 in gels containing all three Carbomers, greatly reduce the mucosa-adhesive strength of the gel. Furthermore, it was found that a combination of C934 and C974 at a total concentration of 1.6-1.8%w/v, along with 0.2-0.4%w/v C971 form gels with good clarity and spreadability as well as strong mucosa-adhesive strengths. Gels showing the greatest mucosa-adhesive strength and good general appearance and spreadability were then assessed in terms of their duration of mucosa-adhesion to rat intestine in pH6.8 isotonic phosphate buffer at 37 ?C and under a constant applied force of 15.0g. The results obtained showed that a gel that has high mucosa-adhesive strength will not necessarily have a great duration of mucosa-adhesion. Hence, it is suggested that this important parameter should also be considered besides the test for assessing the mucosa-adhesive strength in the selection of an efficient transbuccal mucosa-adhesive drug delivery system.