formulations were prepared using different polymers kollidone sr , cellulose acetate , acrycoat s 100 , methocel k4 m , methocel k15 m , methocel k100 m .
drug and polymer in proportion 1:2 , ( drug : polymer ) were dissolved in organic solvent ( ethanol and acetone ) .
this clear solution was poured slowly as a thin stream in oil phase ; about 100 ml of liquid paraffin solution with continuous stirring at a speed of 500 rpm using mechanical stirrer at room temperature until complete evaporation of solvent took place .
the floating microspheres were collected by decantation , while the non floating microspheres were discarded along with any polymer precipitates .
several preformulation trials were undertaken for various proportions of drug and polymer by variation of the ethyl acetate - acetone ratio and dichloromethane - ethanol ratio .
kollidone sr , acrycoat s 100 and cellulose acetate were selected as matrixing agent considering its widespread applicability and excellent gelling activity in sustain release formulations and also having the ph - independent and reproducible drug release profile .
it was found that kollidone sr microspheres show desirable high drug content , yield , floatation and adequate release characteristics and hence was suitable for development of a controlled release system . in the present study , in vitro release studies of the floating microspheres were carried out in 0.1 n hydrochloric acid at 37c for a maximum period of 12 hours . at different time intervals ,
samples were withdrawn and cumulative % drug release was calculated . the percentage drug release of all the formulations is presented in figure 1 .
out of 9 formulations tried , the formulation k1 was found to be satisfactory ; since it showed prolonged and complete release with 94.75% at end of 12 h. % drug release of all nine formulations
multi unit gastroretentive drug delivery system has additional advantage of absence of dose dumping as in single unit drug delivery .
the present investigation described the influence of the drug : polymer ratio on hydrochlorothiazide release .
the release and drug entrapment efficiency of the microspheres were affected by the different polymers .
it was found that the kollidone sr had a dominant role in the drug release from microspheres rather than acrycoat s 100 and cellulose acetate . and it can be given in hard gelatin capsule form .
therefore , it may be concluded that drug loaded floating microspheres in combination with kollidone sr are a suitable drug delivery system for hydrochlorothiazide .
 the present investigation described the influence of viscosity and drug : polymer ratio on hydrochlorothiazide release . 
 floating microspheres loaded with hydrochlorothiazide were prepared by emulsion solvent evaporation method . 
 the prepared microspheres were evaluated by micromeritics properties , in vitro drug release , floating ability and drug entrapment efficiency . 