Studies on pore structure of granules by mercury porosimetry

Analysis of formulation effects in the dissolution of ibuprofen pellets

In this work the effects of citric acid and of two common fillers, lactose (soluble) and tricalcium phosphate (insoluble) are examined on the release profiles from pellets, using ibuprofen as a model drug with pH-dependent solubility. Also studied is the dependence of these profiles on the specific surface area, bulk density, apparent density, porosity and porosity parameters (pore size distribution, total pore surface area, mean pore diameter and pore shape), as determined by mercury intrusion porosimetry. Pellets with high porosity and total pore surface area but small median pore diameter (tricalcium phosphate pellets-IPM) are found to produce similar dissolution results to those of low porosity and low total pore surface area, but having a high median pore diameter (lactose pellets-ILM), irrespective of the solubility of excipients. Addition of citric acid causes a delay in the initial dissolution for both formulations. During dissolution, however, citric acid reduces the median pore diameter of lactose-based pellets. In contrast, in tricalcium phosphate/citric acid pellets (CIPM), this parameter increases considerably during dissolution, when compared to the IPM formulation. These findings may justify the contrasting dissolution behaviors of CIPM and CILM (lactose/citric acid) pellets, after their common behavior in the initial stages, and show that porosity and its related parameters, along with physical properties of excipients such as solubility, density and specific surface area, are helpful to predict pellet behavior in drug release profiles.

Multi-unit controlled release systems of nifedipine and nifedipine:pluronic F-68 solid dispersions: characterization of release mechanisms

Nifedipine (N) and nifedipine. Pluronic F-68 solid dispersion (SD) pellets were developed and characterizedfor drug release mechanisms from a multi-unit erosion matrix system for controlled release. Nifedipine was micronized using a jet mill. Solid dispersion with Pluronic F-68 was prepared by the fusion method. Nifedipine and SD were characterized by particle size analysis, solubility, differential scanning calorimetry (DSC), and x-ray diffraction (XRD) studies. Samples were subsequently processed into matrix pellets by extrusion/spheronization using Eudragit L 100-55 and Eudragit S 100 as release rate-controlling polymers. Drug release mechanisms from pellets were characterized by microscopy and mercury intrusion porosimetry; DSC and XRD studies indicated no polymorphic changes in N after micronization and also confirmed the formation of SD of N with Pluronic F-68. Pellets of N showed a 24-hr drug release profile following zero-order kinetics. Pellets of SD showed a 12-hr release profile followingfirst-order kinetics. Aqueous solubility of N after SD formation was found to be increased 10-fold. Due to increased solubility of N in SD, the drug release mechanism from the multi-unit erosion matrix changed from pure surface erosion to an erosion/diffusion mechanism, thereby altering the release rate and kinetics.

Effect of formulation and process variables on porosity parameters and release rates from a multi unit erosion matrix of a poorly soluble drug

The effect of drug loading, water required for granulation and spheronization time on porosity parameters (intrusion-extrusion isotherms, pore size distribution, total pore surface area, mean pore diameter, shape and morphology of pores) and drug release rates from pellets of a poorly soluble drug was investigated. Porosity parameters were determined by mercury intrusion porosimetry. The drug loading was found to have a profound effect on the porosity parameters. Pellets with low drug loading showed increased pore surface area with small mean pore diameters and an increased number of total pores. On the other hand, pellets with high drug loading had decreased pore surface areas with larger mean pore diameters and a reduction in the total number of pores. With high drug loading, the drug release rate decreased. Water required for granulation had a direct effect on the total porosity of the pellets. Spheronization time from 2 to 10 min had a pronounced effect on porosity parameters and release rates. No changes in porosity parameters and release rates were observed from 10 to 20 min of spheronization time. It was shown that each porosity parameter investigated was well correlated with drug release rates and thus it is important to study the effect of porosity parameters in evaluating the in vitro performance of the multi-unit erosion matrix for the controlled release of a poorly soluble drug.