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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The applicability of alpha-tocopherol as a lymphotropic carrier for a highly lipophilic drug has been evaluated. Transport to the intestinal lymph of the highly lipophilic model drug, Lu28-179, in rats after administration to the stomach in an alpha-tocopherol emulsion was compared with lymphatic transport after administration of a sesame oil emulsion and an alpha-tocopherol/sesame oil emulsion. Lymphatic transport of the triglycerides and of alpha-tocopherol was determined. A conscious rat model was used, and the mesenteric lymph was collected. There was no significant difference between the cumulative masses of triglyceride from the two emulsions containing triglyceride 24 h after administration. Administration of an alpha-tocopherol emulsion seemed to induce mobilization of endogenous triglyceride. The lymphatic transport of alpha-tocopherol was less than 1 mg 24 h after administration of both emulsions containing alpha-tocopherol. The absorption of Lu28-179 from the alpha-tocopherol emulsion was very low, with a lymphatic recovery of 0.05%. When administered in an alpha-tocopherol/sesame oil emulsion, the recovery of Lu28-179 increased sevenfold to 0.35%. However, after administration of Lu28-179 in a sesame oil emulsion, the lymphatic recovery increased a further 13-fold to 4.5%. In conclusion, the study showed that alpha-tocopherol did not promote lymphatic absorption of Lu28-179 and thus was not a good lymphotropic carrier, as compared with sesame oil. Alpha-tocopherol in combination with sesame oil was not a good lymphotropic carrier either. The non-absorbed alpha-tocopherol fraction in the intestine might be able to prevent the absorption of Lu28-179.

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