Design of floating bilayer tablets of diltiazem hydrochloride and lovastatin

The purpose of the study is to design bilayer floating tablets of diltiazem HCI and lovastatin to give immediate release of lovastatin and controlled release of diltiazem HCl and to study the influence of presence of one drug on the release pattern of other drug. The bilayer tablets consist of sodium starch glycolate as superdisintegrant for lovastatin in the immediate release layer and hydroxypropyl methylcellulose (HPMC) K4M and Xanthan gum as release-retarding agents for diltiazem HCl in the controlled release layer. Sodium bicarbonate was used as the gas generating agent. Dicalcium phosphate was used as the channeling agent. The direct compression method was employed for preparation of the bilayer tablets. Various physicochemical parameters were evaluated for the prepared tablets. The physicochemical parameters were found to be within range. There was significant difference in drug release and floating lag time (P < 0.05). All the formulations showed good matrix integrity. All the formulations released lovastatin within 30 min. The diffusion exponent for diltiazem HCl was found to be independent of polymer concentration. The release pattern of diltiazem HCI was fitted to different models based on coefficient of correlation (R). All the formulations followed the Higuchi model, except F1 which followed the Peppas model. HPMC K4M and Xanthan gum retarded the release of diltiazem HCl for 12 h. The release of one drug remained unaffected in presence of the other drug. In conclusion, such kind of combined dosage forms can effectively be formulated to deliver more than one drug so as to have improved patient compliance and better disease management.