Fluidized-bed spray coated porous hydrogel beads for sustained release of diclofenac sodium

Abstract

Swellable porous hydrogel beads were loaded with diclofenac sodium and then coated with pseudo-latex ethylcellulose (EC) in a fluidized-bed spray coater. The drug release profile in-vitro can be modified by adding 25% or more triethyl citrate (TEC) or dibutyl sebacate (DBS) as a plasticizer. The plasticized coating film can overcome the swelling stress of the core and function as a barrier for sustained drug release. Adding TEC resulted in a near-zero order kinetics after an initial burst in the release profile, and adding DBS showed a first initial burst, a second stage of linear release, a third stage of slow release. The initial burst is due to the flaws or cracks on the surface of the coated-beads and it can be reduced by increasing the amount of plasticizer or film thickness and also by adjusting the thermal treatment time. A 4- to 6-h treatment at 60°C was found to be the optimal condition to give the smallest initial burst for coating film containing TEC as a plasticizer. Adding hydrophilic hydroxylpropyl methylcellulose (HPMC) could smooth the initial burst and change the release profile to a Fickian-type release, and in this case increasing the thermal treatment time could reduce the release rate. Two kinds of EC-coated beads were tested in-vivo by using rabbits as animal models and showed good sustained release behaviors as the drug concentration in plasma could be maintained above 0.4 μg/ml and lower than 1.5 μg/ml for 24 h.