Alginate-diltiazem hydrochloride beads: optimization of formulation factors, in vitro and in vivo availability

Alginate beads containing diltiazem hydrochloride (DTZ) were prepared by the ionotropic gelation method. The effects of various factors (alginate concentration, additives type, calcium chloride concentration and curing time) on the efficiency of drug loading were investigated. The formulation containing a mixture of 0.8% methylcellulose (MC) and 4% alginate cured in 2% calcium chloride for 6 h was chosen as the best formula regarding the loading efficiency. The release rate of DTZ from various beads formulations was investigated. The release of drug from alginate beads followed two mechanisms; by diffusion and relaxation of the polymer at pH 1.2, whilst diffusion and erosion are at pH 6.8. The in vitro release of DTZ from MC-alginate beads showed an extended release pattern which was compared with that from commercially available sustained-release (Dilzem SR) and fast release tablets (Dilzem). Thermal analysis revealed that the drug was molecularly dispersed in the beads matrix. Although the release characteristics of DTZ from Dilzem SR and MC-alginate beads were completely different, the bioavailability of DTZ in dogs was comparable as measured by AUC, MRT and relative bioavailability. The absolute bioavailability of MC-alginate beads and Dilzem SR was 88 and 93%, respectively.

In vitro and in vivo evaluation of Pluronic F127-based ocular delivery system for timolol maleate

The purpose of this study was to develop Pluronic F127 (PF127) based formulations of timolol maleate (TM) aimed at enhancing its ocular bioavailability. The effect of isotonicity agents and PF127 concentrations on the rheological properties of the prepared formulations was examined. In an attempt to reduce the concentration of PF127 without compromising the in situ gelling capabilities, various viscosity enhancing agents were added to PF127 solution containing 0.5% TM. The viscosity and the ability of PF127 gels to deliver TM, in vitro, in absence and presence of various viscosity enhancing agents were also evaluated. At the used concentration, some of the examined isotonicity agents had effect on the viscosity of TM gel. However, the viscosity of gel increased as the PF127 concentrations increased. The viscosity of formulations containing thickening agents was in the order of PF-MC 3%>PF-HPMC 2%>PF-CMC 2.5%>PF127 15%. The slowest drug release was obtained from 15% PF127 formulations containing 3% methylcellulose. In vivo study showed that the ocular bioavailability of TM, measured in albino rabbits, increased by 2.5 and 2.4 fold for 25% PF127 gel formulation and 15% PF127 containing 3% methylcellulose, respectively, compared with 0.5% TM aqueous solution.

Preparation and evaluation of ketoprofen floating oral delivery system1This paper was presented at the XXVI Conference of Pharmaceutical Sciences, Cairo Meridian (8–10 December, 1998).1

A sustained release system for ketoprofen designed to increase its residence time in the stomach without contact with the mucosa was achieved through the preparation of floating microparticles by the emulsion-solvent diffusion technique. Four different ratios of Eudragit S100 (ES) with Eudragit RL (ERL) were used to form the floating microparticles. The drug retained in the floating microparticles decreased with increase in ERL content. All floating microparticle formulations showed good flow properties and packability. Scanning electron microscopy and particle size analysis revealed differences between the formulations as to their appearance and size distribution. X-ray and DSC examination showed the amorphous nature of the drug. Release rates were generally low in 0.1 N HCl especially in presence of high content of ES while in phosphate buffer pH 6.8, high amounts of ES tended to give a higher release rate. Floating ability in 0.1 N HCl, 0.1 N HCl containing 0.02% Tween 20 and simulated gastric fluid without pepsin was also tested. The formulation containing ES:ERL1:1 (FIII) exhibited high percentage of floating particles in all examined media.

Manipulation of powder characteristics by interactions at the solid-liquid interface: 1-sulphadiazine

A solvent-treatment technique aiming at manipulating the properties of powdered materials is reported. Potentials of the technique were assessed using sulphadiazine (SD). A suspension of the drug in a preselected solvent (5% aqueous ammonia solution) was stirred under controlled conditions. The solvent was subsequently removed and the material dried. The effect of experimental variables such as stirring speed and time, powder/solvent ratio and inclusion of additives (Tween 80, sodium chloride and PVP) on the properties of solvent treated SD was assessed. Data obtained were compared with those for SD recrystallized under identical conditions. Solvent treatment of SD in the absence of additives resulted in a limited change in crystal morphology as indicated by SEM. This was associated with improved flowability and a limited reduction in dissolution rate relative to untreated SD. On the other hand, recrystallized SD exhibited superior flowability but a considerably low dissolution rate. Solvent treatment of SD in the presence of 2% PVP produced a microgranular directly compressible material.