Formulation and evaluation of captopril floating matrix tablets based on gas formation

Captopril has a short elimination half-life and is stable at pH 1.2 and as the pH increases; the drug becomes unstable and undergoes a degradation reaction. The purpose of this study was to develop a gastroretentive controlled release drug delivery system with swelling and floating properties. Seventeen tablet formulations were designed using hydroxyl propyl methyl cellulose (HPMC) K4M, Carbomer 934, Eudragit RS PO as release retarding polymer(s), lactose or Avicel PH 102 as a filler and sodium bicarbonate as a gas former by direct compression. Tablets were evaluated for various physical parameters, floating properties, swelling ability and drug release characteristics in 12 h. Based on the release kinetics, all formulations best fitted the Higuchi, Hixson Crowell model and non-Fickian as the mechanism of drug release. Statistical analyses of data revealed that formulation containing HPMC K4M (42%, w/w), NaHCO3 (8%, w/w) and Avicel PH 102 (32.35%, w/w) was the promising system exhibiting excellent floating properties and sustained drug release (12 h) characteristics.   Key words: Floating drug delivery system, captopril, HPMC K4M, Carbomer 934, Eudragit RS PO.