10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 1 2013 (January - March) This work describes the stability of the selected lessThan i greaterThan in situ lessThan /i greaterThan solutions for ophthalmic delivery of naphazoline hydrochloride ( FF17, FF18) and antazoline phosphate ( GG17 and GG18) based on the pH triggered concept using Carbopol 940 and HPMC K4M. The formulations were evaluated for their pH, isotonicity, gelling capacity, rheological characteristics, lessThan i greaterThan in vitro lessThan /i greaterThan drug release , sterility and lessThan i greaterThan in vivo lessThan /i greaterThan studies in New Zealand rabbits' eyes. All the formulations showed satisfactory results at ocular pH environment that remains in contact with the eyes for few hours. The formulations were very stable throughout, at room temperature and at 40 °C. Higher amount of both the drugs were retained in the aqueous humour area over 8 hrs following instillation FF17, FF18, GG17& GG18. Therefore, lessThan i greaterThan in situ lessThan /i greaterThan gelling system can be used to enhance the ocular retention time thereby increasing ocular bioavailability and reducing the frequency of dosing . G NISHA SHETTY AND R.N. CHARYULU Stability, Naphazoline hydrochloride, Antazoline phosphate, Carbopol 940, HPMC K4M, In situ gelling solutions 161-171