RHEOLOGICAL EVALUATION AND OCULAR CONTACT TIME OF SOME CARBOMER GELS FOR OPHTHALMIC USE

The poor uptake of many ophthalmic drugs is mainly due to the rapid el imination process by tear turnover, A prolonged precorneal residence t ime would result in higher absorption and, for some drugs, a prolonged duration of their therapeutic effect. It is known that gels are retai ned 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 g els have been monitored in humans and the gels were also theologically 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 elast ic properties of the gels. The miotic response from gels with pilocarp ine nitrate was monitored in rabbits and the area under the curves (AU Cs') were calculated. The relative AUCs were 1.5-2.1 for the gel prepa rations relative to a solution, No concentration dependence was seen a nd there was no significant difference in AUC between the different ca rbomers, The ocular contact time of the gels were much less in rabbits than those obtained in humans.