Rheological evaluation and ocular contact time of some carbomer gels for ophthalmic use

Abstract

The poor uptake of many ophthalmic drugs is mainly due to the rapid elimination process by tear turnover. A prolonged precorneal residence time would result in higher absorption and, for some drugs, a prolonged duration of their therapeutic effect. It is known that gels are retained better in the eye than ordinary solutions but relatively little is known about the importance of the rheological properties of gels for their retention. In this study the ocular residence time of carbomer gels have been monitored in humans and the gels were also rheologically characterised. The contact time of Carbopol 974P and Carbopol 1342NF was concentration dependent and was approximately 2–2.5 h for a 2% gel. There was a good correlation of the human contact time and the elastic properties of the gels. The miotic response from gels with pilocarpine nitrate was monitored in rabbits and the area under the curves (AUCs') were calculated. The relative AUCs were 1.5–2.1 for the gel preparations relative to a solution. No concentration dependence was seen and there was no significant difference in AUC between the different carbomers. The ocular contact time of the gels were much less in rabbits than those obtained in humans.