Conventional drug delivery systems are known to provide an immediate release of drug, in which one can not control the release of the drug and can not maintain effective concentration at the target site for longer time. Controlled drug delivery systems offer spatial control over the drug release. Osmotic pumps are most promising systems for controlled drug delivery. These systems are used for both oral administration and implantation. Osmotic pumps consist of an inner core containing drug and osmogens, coated with a semipermeable membrane. As the core absorbs water, it expands in volume, which pushes the drug solution out through the delivery ports. Osmotic pumps release drug at a rate that is independent of the pH and hydrodynamics of the dissolution medium. The historical development of osmotic systems includes development of the Rose-Nelson pump, the Higuchi-Leeper pumps, the Alzet and Osmet systems, the elementary osmotic pump, and the push-pull system. Recent advances include development of the controlled porosity osmotic pump, and systems based on asymmetric membranes. This paper highlights the principle of osmosis, materials used for fabrication of pumps, types of pumps, advantages, disadvantages, and marketed products of this system.

By an initial solvent screening of 18 solvents, 14 pure good solvents were selected for the crystallization of tolbutamide. Solid generation by the solvent-change method was carried out using the pure good solvents. Crystals were generated in only 10 of the 14 solvents. Different crystal forms of tolbutamide were obtained. Crystals were subjected to evaluation tests such as differential scanning calorimetry, optical microscopy, and in vitro dissolution. All crystals were determined as isomorphic by differential scanning calorimetry. Dissolution rate was influenced by crystal form. Thus, the choice of suitable crystal habit and proper selection of solvent is important in manufacturing the drug tolbutamide.

A method for the development of press coated tablet of atenolol for pulsatile delivery was investigated for chronotherapy of hypertension. Effect of viscosity of Hydroxypropylcellulose (HPC) on pulsatile release of atenlol was studied by press coating atenolol core tablet using different viscosity grade HPC and varying coat weight. L-HPC, M-HPC and H-HPC viscosity garde with 75, 100 and 150 mg coat weight were press coated over atenolol core tablets to delay release of atenolol. The batches, HP1-HP9, exhibited an increase in lag time in response to increase in viscosity and coat weight. Two of the batches HP5 and HP7 have shown a burst release of atenolol after 6.5 and 6.0 h lag time respectively, which is suitable for pulsatile drug delivery of atenolol for chronotherapy of hypertension.