Thermal and 31P-NMR studies to elucidate sumatriptan succinate entrapment behavior in phosphatidylcholine/cholesterol liposomes. Comparative 31P-NMR analysis on negatively and positively-charged liposomes.

In this paper, two techniques, differential scanning calorimetry (DSC) and phosphorus nuclear magnetic resonance ((31)P-NMR), have been used to characterize sumatriptan succinate-loaded charged liposomes. To complete the results obtained by DSC a hot stage microscopy (HSM) technique was used. Data concerning the drug entrapment efficiency were published in a previous paper. The differences in data concerning encapsulation into negatively and positively-charged vesicles, indicated an influence of drug in the structural conformation of lipids in the bilayer. Moreover, the inability to formulate chargeless vesicles contributed to the opinion that a physical formulation study might be relevant. Phosphatidylcholine and cholesterol were used as lipid film forming agents, whereas stearylamine (positive) and dicetylphosphate (negative) were added as charge-inducing agents. DSC studies demonstrated that phosphatidylcholine caused the disappearance of the melting peak (Tm) of sumatriptan succinate because a drug dissolution process occurs. In addition, thermograms showed interesting interactions between stearylamine and dicetylphosphate with sumatriptan succinate favoring drug entrapment into the liposomes. In the present work, (31)P-NMR technique demonstrated that the structural conformation of lipids in the membrane affected drug encapsulation into multilamellar (MLVs) and unilamellar (LUVs) vesicles. Bilayer structure in a liquid crystalline phase of the positively-charged REV liposomes membrane has demonstrated a high structural stability and a better encapsulation efficacy for sumatriptan succinate than negatively-charged TLE and REV liposomes. Therefore, phosphatidylcholine interaction with sumatriptan succinate appears to be the cause of the inability to obtain neutral sumatriptan succinate liposomes.

Theophylline-loaded compritol microspheres prepared by ultrasound-assisted atomization.

Nine solid dispersions were prepared by the melting method in the form of particles containing theophylline at 10%, 20%, and 30% (w/w) in three Compritols (Compritol 888 ATO, HD5 ATO, E ATO) to compare their efficiency in controlling theophylline release. After solidification the mass was ground and granules were evaluated by thermal [differential scanning calorimetry, hot stage microscopy (HSM)] and spectroscopic [Fourier transform infrared (FTIR), Raman, X-ray powder diffraction (XRD)] analysis and the solubility parameters. Another nine samples of the same composition were obtained as microspheres by ultrasound-assisted (US) atomization. XRD confirmed the presence of crystalline theophylline inside the solid dispersions. FTIR and Raman microspectroscopy revealed that crystals of the drug were present on the granule surface. On the contrary, the surface of the final microspheres did not present free drug crystals. The granules do not work so efficiently as microspheres in controlling the release of theophylline: 888 ATO ≈ HD5 ATO > E ATO represents the order of the ability of the Compritols to control the theophylline release from microspheres. HSM revealed that, on aging, the dissolved drug crystallizes, considerably modifying the granule formulation and that US vibration, speeding up the crystallization of the drug during the preparation of microspheres, greatly reduces the changes associated with aging.

Development of enteric-coated pectin-based matrix tablets for colonic delivery of theophylline.

The present work was aimed at developing a new colonic drug delivery system which takes advantage of the combined approaches of a specifically colon-biodegradable pectin matrix with a pH-sensitive Eudragit S100 polymeric coating. The developed system was able to suitably retard the onset of drug release and to provide a colon-specific delivery, thus overcoming the problems of pectin solubility in the upper gastrointestinal tract and low site-specificity of simple pH-dependent systems. Due to the poor compactability properties of pectin, it was used in mixture with Emdex, a hydrophilic directly-compressible material, in order to make it possible to prepare tablets by direct compression. Theophylline (TP) was used as model drug due to its suitable pharmacokinetic properties for colonic delivery and good absorption in the large intestine. The effects of varying the type of pectin (low and high methoxylated, or amidated), the pectin:Emdex ratio and the level of the pH-dependent polymeric coating on drug release behavior were investigated. Release tests were performed using sequential liquids simulating the physiological variation of pH and the effect of the presence or not of pectinolytic enzymes into the simulated colonic medium was evaluated. Thirty percent (w/w) was the the minimum content of Emdex for obtaining directly compressible tablets with sufficient hardness to withstand the coating process and 27% (w/w) was the minimum coating amount for obtaining an adequate lag time before the onset of drug release. After lag time, linear nearly zero-order profiles were obtained whose slope (i.e. the drug release rate) depended on both the Emdex content and the pectin type. Comparison of the results obtained in the presence or not of pectynolitic enzymes allowed selection of the high methoxylated pectin as the most interesting candidate for specific colonic delivery since it was the least water-soluble and the most susceptible to enzymatic degradation, thus assuring a greater site-specificity of drug release. Finally, the importance of using appropriate dissolution test conditions to adequately characterize the drug release profiles from delivery systems endowed with a microflora-activated drug release triggering mechanism has been demonstrated.