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The ternary phase diagram of two nonionic polar lipids, glycerol monooleate (GMO) and diglycerol monooleate (DGMO), in water has been characterized through NMR, polarizing optical microscopy, SAXS, and rheological measurements. GMO in water forms a lamellar and two types of bicontinuous cubic phases. The diamond type exists in equilibrium with water. DGMO, with its bulky polar group, forms only lamellar structures that also coexist with water. In the ternary GMO/DGMO/water system, the regions of lamellar and cubic phases are significantly enlarged, and a swollen cubic phase of the gyroid type exists in equilibrium with water. Measurement of the viscoelastic properties revealed that the cubic phases are elastic, independent of the sample composition. The cubic phases become softer (the G‘ storage modulus decreases) with increasing water and DGMO content. A discontinuity is observed in the G‘ versus water content graph at the transition between the gyroid and the diamond cubic phases.

Abstract. This paper describes the development of a stable, controlled‐release formulation of metronidazole for use in the treatment of periodontal disease. It is formulated as a suspension, which undergoes transformation to a release‐controlling, semi‐solid on contact with gingival fluid. The system is based on the ability of mixtures of monoglycerides and triglycerides to form liquid crystals, i.e., reversed hexagonals, in contact with water. The reversed hexagonal form was found to have the most favourable sustained release properties, compared with those from the cubic form. The source of metronidazole is the prodrug, metronidazole benzoate, which further helps to slow down the release rate. Product characteristics are assessed by differential scanning calorimetry and viscometry. The release data derive from the results of in vitro dissolution tests. X‐ray diffraction, phase diagrams, and polarized light microscopy were used to elucidate the structure of the liquid crystalline phases.

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