Formulation and evaluation of bilayer tablets of diltiazem HCl

The present investigation concerns development of bilayer floating tablets of Diltiazem HCl is class I drug, though its reported bioavailability is only 40 %. It is having very short half life of 3 to 4 hr. Hence many sustained release formulations were developed for diltiazem HCl. But they take lag time to start the action. Hence a new approach is tried that gives one immediate release dose and a sustained release dose in single dosage form call bilayer tablets. Immediate release layer delivers the initial dose, it contains superdisintegrant which increase drug release rate whereas sustained release layer float due to gas generating agent and releases drug at sustained manner for prolonged period. A direct compression method was used to formulate 9 batches. Superdisintegrants like sodium croscarmellose, crospovidone was used for immediate release layer and HPMC K4 M, HPMC K 15 M, PVP K30 like polymers were used in floating layer. A simple visible spectrophotometric method was employed for the estimation of diltiazem at 236 nm and Beer's law is obeyed in the concentration range of 5-25 µg/ml. Preformulation studies were carried out to optimize the ratios required for various grades of polymers. The prepared floating tablets were evaluated for hardness, weight variation, thickness, friability, drug content uniformity, buoyancy lag time, total floating time, water uptake (swelling index), and in vitro dissolution studies. Successful formulation was developed having floating lag time as low as 30 sec and drug release was sustained up to 12 hrs. A biphasic drug release can be obtained by using bilayer tabletting technology which involved compression of immediate and sustained release layer together. Bilayered floating tablets with release characteristics offer critical advantages such as, site specificity with improved absorption and efficacy. This technology can be inculcated to various medicaments which have stomach as the major site of absorption.