Preparation and evaluation of a floating drug delivery system for Diltiazem HCl

Approaches to increase the gastric residence time (GRT) include: floating drug delivery systems (FDDS), swellingexpanding forms, bio (muco) adhesive forms, modified shape and high density systems. Diltiazem HCl (DTZ), a model drug for this study, is a calcium antagonist used in the treatment of chronic heart diseases such as angina and hypertension. It has elimination half-life of 3.5 hours and hence is a suitable model candidate for gastro retentive formulation. The major objectives of this study were to develop a single unit FDDS of DTZ and to study the effect of formulation and processing parameters on the floating and drug release of the system. DTZ matrix tablets (120 mg) containing HPMC (K4M, Colorcon, UK), Carbomer (934P, B.F. Goodrich, USA), Na CMC (Merck, Germany), Guar gum (Hercules, USA) and Xanthan gum (Arthur Branwell, UK) were prepared by direct compression method. All tablets contained an effervescent base consisting of sodium bicarbonate and citric acid. The tablets were evaluated for in vitro floating ability (floating lag time and duration of floating time), bioadhesiveness and drug release. Bioadhesion was measured by a method based on shearing tensile strength existing between tablets and a mucosal layer. The drug release studies were carried out using a dissolution apparatus (Erweka, Type DT700, Germany) basket method (100 rpm) in 900 ml of 0.1 N HCl buffer solution (pH = 1.2, 37°C). At appropriate time intervals, samples were withdrawn and assayed spectrophotometrically at 237.8 nm with suitable dilutions. In vitro floating test showed that tablets containing 12% effervescent base had a floating lag time of 30-120 seconds. The duration of floating was 19-24 hours for all the formulations and the hardness of tablets had no significant effects on the floating time. The more carbomer content of the tablets, the more in the bioadhesive properties. Drug release data was fitted on both Higuchi and first order kinetic models. The mechanism of drug release showed a non Fickian (anomalous) behavior based on Korsmeyer- Peppas equation. We concluded that the proposed tablets with 12% effervescent base, 30% HPMC and 10% Na CMC showed good floating, bioadhesion and drug release properties in vitro and seems to be considered as FDDS for DTZ.