Effect of salts on gelation and drug release profiles of methylcellulose-based ophthalmic thermo-reversible in situ gels

The poor bioavailability and therapeutic response exhibited by conventional ophthalmic solutions may be overcome by the use of thermo-reversible in situ gel. The purpose of this study was to examine the influence of different salts on the gelation, rheology and drug release of in situ gel based on methylcellulose. The gel temperature of 1% w/v methylcellulose (MC) was 60 degrees C. It was found that 5-7% w/v sodium chloride (NaCl), 8-9% w/v potassium chloride (KCl), or 5% w/v sodium bicarbonate (NaHCO3) was capable of decreasing the gel temperature below physiological temperature, i.e. 37 degrees C. Rheological studies indicated a large increase in viscosity at 37 degrees C with the addition of salts in MC solutions. The duration of drug release from MC solution was 1.5 h. The significant observation was that the duration of drug release increased from 1.5 h to 3-5 h from salted MC solutions depending on the concentration and the type of salt. So, it can be concluded that the salted MC solutions were a better alternative than the MC solution to enhance the ocular bioavailability of the drug.