Introduction

Vesicular Phospholipid Gels (VPGs) as parenteral implants have been described for the first time 20 yaers ago [1]. From that time VPGs were quite well structurally and physicochemically characterized, but till now some practical and technological aspects about these semisolid liposome dispersions (e.g. sterilization method or stability) are not fully explained.

Aim of the study

The aim of the study was to prepare and characterize VPGs formulations composed of soy or egg-yolk lecithin (40-60%) and different aqueous phases: phosphate buffer, glycerol, macrogol or poloxamer. Production of the gels was optimized in terms of homogenization (homogenizer type, time and temperature range) and sterilization methods (time and temperature of autoclaving). Moreover, to some gels (containing 50% of lecithin) acive substances were added (e.g. ondansetron hydrochloride-OND or risperidone-RIS) and properties of these formulations were compared with VPGs placebo.

Methods

In order to prepare semisolid implants, appropriate amounts of lecithin were mixed (using Unguator or Ultra-Turrax homogenizer) with aqueous phase: water (W), phosphate buffer (PB), 2.4% glycerol (GL), 10% macrogol (PEG) or 10% poloxamer (PL). Drugs (OND or RIS), if present, were added to the aqueous phase before homogenization step and finally the gels were thermally sterilized.

Implants were examined visually and microscopically (using optical or polarized-light microscope). Physicochemical tests comprised of rheological analysis (using a texture analyzer and rheometer), size measurement of lecithin particles (light microscope and laser diffractometry method), determination of drug content and dissolution test (dialysis-tube method).

Results

Regardless of the composition and homogenization method, all obtained lecithin gels were semisolid and cream- to yellow-colored. Microscopic analysis indicated, that the gels are composed of many small, mainly multivesicular lecithin particles, which size depended on the lecithin concentration, type of aqueous phase and homogenization method. The smallest vesicles (d(0.9)<1 μm) were present in formulation composed of lecithin (60%) and PL. More stable were gels prepared by Ultra-Turrax (compared to Unguator mixer), because the morphology of their vesicular particles remained unchangeable, even after autoclaving. Both rheological tests showed, that viscosity of gels depended on lecithin concentration and type of aqueous phase. The highest viscosity was measured for systems composed of lecithin (60%) and PB or PL. Incorporation of drug substances into the gel matrix did not change their physicochemical properties significantly (slight reduction in particle size and increase in gel viscosity were noticed). For all drug formulations prolonged release of OND and RIS was demonstrated. Depending on gel composition, after 24 h, about 50-80% of the active substance was released from phospholipid implant matrix during dissolution test.

Conclusion

Lecithin (egg or soy) after dispersion in aqueous solution forms semisolid systems (gels), which can be use as implantable prolonged-release matrices. Active substances incorporated into the gels did not destroy the structure and properties of the matrix, but are released from the system in a sustained manner for at least of 24 h.

Acknowledgments

This study was supported by funds obtained from the quality-promoting subsidy under the KNOW programme 2012-2017 and from National Sciences Centre - grant number N N405 668440.

References:

[1] Tardi C. et al.: Steam sterilization of vesicular phospholipid gels, Int. J. Pharm., 217 (2001) 161-172

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/31030 must be provided.

1.   “Preliminary study of silicone gel sheets containing onion (Allium cepae) extract for treatment of scars”
2. THE INFLUENCE OF LECITHIN ON RELEASE OF PARACETAMOL FROM SUPPOSITORIES IN IN VITRO STUDIES
3. PREPARATION AND EVALUATION OF PHYSICOCHEMICAL PROPERTIES OF MUCOADHESIVE, FREEZE-DRIED BUCCAL SYSTEMS WITH SELEGILINE