Purpose: To develop and optimise sustained release (SR) matrix tablets of diltiazem hydrochloride (DHL).

Methods: DHL tablets were prepared by direct compression and consisted of hydroxypropylmethylcellulose (HPMC), Kollidon SR and Eudragit RSPO. A 3² full factorial design was applied to study the effect of polymers used on drug release from the DHL. The tablets were also evaluated for physicochemical characteristics and release kinetics.  In vivo (human) studies were carried out on the optimised formulation using a commercial sustained release product as a reference.

Results: The physicochemical characteristics of all prepared tablets were satisfactory. The developed drug delivery system provided prolonged drug release rates over a period of 24 h. The release profile of the developed formulation was described by the Higuchi model. Mean time to attain peak drug concentration (T_max) was 2.05 ± 0.52  and 2.30 ± 0.57 h for the optimized and commercial formulations, respectively, while mean maximum drug concentration (C_max) was 501.74 ± 0.05 ng/ml and 509.65±0.06, ng/ml, respectively. A fair correlation between the dissolution profile and bioavailability for the optimized formulation was observed based on linear regression analysis.

Conclusion: A fair correlation between in vitro dissolution and in vivo data was found for the optimized formulation of diltiazem. The results also indicate that the approach used could lead to a successful development of a sustained release formulation of the drug.