Aim: To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems.
Methods: A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs.
Results: Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30 x 10(-6) cm2 x s(-1), respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity.
Conclusion: The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.