Objective    To investigate the release feature of dexamethasone sodium phosphate from thermosensitive in situ gels in vitro.     Methods    Rotation rheometer was used to measure the changes of viscosity with temperature. The membraneless model was applied in assessing corrosion behavior of gel using a thermostatic shaker (50 r/min) at an amplitude of 2.5 cm

taking phosphate buffered solution (pH 7.2) as rel

easing media. The release behavior was investigated by HPLC on a C

18

reverse column Diamonsil

TM

(250 mm×4.6 mm

5 μm). The mobile phase consisted of triethylamine solution-methanol-acetonitrile (38∶28∶34)

pumped at 1.0 ml/min

and the detection wavelength was set at 242 nm.     Results    When the temperature was near to the sol-gel transition temperature

the viscosity rose suddenly. Taking dexamethasone sodium phosphate (2 ml

pH 7.2) as media

the gel dissolution and drug release rate followed the zero order kinetics

and the cumulative gel dissolution (Q

1

) and cumulative drug release (Q

2

) equations were Q

1

=0.8238t (r=0.999

P0.01) and Q

2

=0.8431t (r=0.999

P0.01)

respectively. There was good liner relationship between cumulative drug release and drug release time.     Conclusion    The drug release behavior of thermosensitive in situ gels is clearly shown in our experiment.