Monolithic osmotic tablet system for nifedipine delivery

The monolithic osmotic tablet system, which is composed of a monolithic tab let coated with cellulose acetate (CA) membrane drilled with two orifices o n both side surfaces, has been described. The influences of tablet formulat ion variables including molecular weight (MW) and amount of polyethylene ox ide (PEO), amount of potassium chloride (KCI), and amount of rice starch as well as nifedipine loading have been investigated. The optimal tablet form ulation and the osmotic-suspending co-controlled delivery mechanisms have b een proposed. Orifice size and membrane variables including nature and amou nt of plasticizers as well as thickness on drug release have also been stud ied. The in vitro release profiles of the optimal system have been evaluate d in various release media and different agitation rates, and compared with commercialized conventional capsule and push-pull osmotic tablet. It was f ound that PEO with MW of 300 000 g/mol was suitable to be thickening agent, both amount of KCl and amount of PEO had comparable and profoundly positiv e effects, while nifedipine loading had a strikingly negative influence on drug release. It could be found that the optimal orifice size was in the ra nge of 0.25-1.41 mm. It has also been observed that hydrophilic plasticizer polyethylene glycol (PEG) improved drug release, whereas hydrophobic plast icizer triacetin depressed drug release when they were incorporated in CA m embrane. The monolithic osmotic tablet system was found to be able to deliv er nifedipine at the rate of approximate zero-order up to 24 h, independent of both environmental media and agitation rate, and substantially comparab le with the push-pull osmotic tablet. The monolithic osmotic tablet system was simple to be prepared as exempting from push layer and simplifying in t he orifice drilling compared with the push-pull osmotic tablet. The monolit hic osmotic tablet system may be used in drug controlled delivery held, esp ecially suitable for water-insoluble drugs. (C) 2000 Elsevier Science B.V. All rights reserved.