The formulation and sterilization of a surgical lubricant gel based on carboxypolymethylene

Abstract

Abstract A lubricant gel of optimal consistency containing a local anaesthetic (lignocaine) has been formulated which can be sterilized by gamma irradiation. A rheological specification was obtained by examination of some currently used preparations. The variation in their consistency was large but all exhibited pseudoplastic flow with a yield value. Gels based on tragacanth, the methylcelluloses and the Carbopols were suitable as lubricants before sterilization and after autoclaving, but on gamma irradiation the gel structure was destroyed. Ethanol (5–10%) protected the Carbopol formulations. Irradiation of lignocaine solutions caused some cloudiness and a small drop in pH. Ethanol and metabisulphite acted as protective agents. A final formulation was developed consisting of a Carbopol gel (1%) neutralized by lignocaine base (2%) and the biological availability of the local anaesthetic was assessed using an in vitro method.