Influence of dissolution medium agitation on release profiles of sustained-release tablets

Reaching nearly perfect sink conditions is very important in the determination of drug dissolution rates. Many times, the only factor that is taken into consideration in achieving sink conditions is the relation between the drug concentration and its solubility. The analytical conditions of the dissolution assay, as well as the dissolution apparatus, stirring speed, and nature and volume of the dissolution fluid may also influence the dissolution results. The main objective of this work was to study the influence of the stirring rate conditions and of the dissolution apparatus in the diltiazem hydrochloride release from tablets. Diltiazem hydrochloride sustained-release (SR) tablets were tested and the following dissolution parameters were evaluated: t(10%), t(25%), t(50%), dissolution time, mean dissolution time (MDT), and dissolution efficiency (DE) at t(120), and at t(360). To analyze the release mechanism, several release models were tested, such as Higuchi, zero order, first order, Baker-Lonsdale, Hixson-Crowell, Weibull, and Korsmeyer-Peppas. The similarities between two in vitro dissolution profiles it-ere assessed by the similarity, factor f(2). The in vitro release kinetics of diltiazem hydrochloride sustained-release tablets were evaluated using the USP 2 (paddle) and USP 4 (flow-through) apparatus.