Pharmaceutical development of solid dispersion based osmotic drug delivery system for nifedipine

Elementary osmotic pumps (EOP) are well known for delivering moderately soluble drugs at a zero order rate. A push-pull osmotic system was developed and commercialized for poorly water-soluble drugs [Procardia XL (Nifedipine), Glucotrl XL (Glipizide)]. However, the technology is complex comprising of bilayer compression and the suspension of drug formed in the core has more viscosity and has to withstand the osmotic pressure within the tablet, for which the membrane must be thicker than that of EOP. The aim of the present study was to develop a solid dispersion based EOP system for a poorly water-soluble drug, nifedipine and deliver it in a zero order fashion over an extended period of time. Solid dispersions were prepared by hot melt technique using Poloxamer-188 at various ratios of drug and polymer (1:1, 1:5 and 1:10, on weight basis) and investigated for solubility study. Formation of complex and decrease in crystallinity was confirmed from differential scanning calorimetry (DSC) and X-ray crystallography (XRD) study. Core tablets using solid dispersions were prepared and coated with cellulose acetate and PEG-400. An orifice was drilled manually to create passage for drug release. The system was optimized for amount of osmogent, membrane weight gain, amount of plasticiser and diameter of the orifice, to achieve desired release profile. The osmotic system was found to deliver nifedipine at a zero order rate for 20 h. The drug release from the developed formulation was independent of pH and agitational intensity.