Modelling and Biopharmaceutical Evaluation of Topical Semisolid Preparations Containing the Small-Leaved Linden (Tilia cordata Mill.) Flower Extract

The Aim: to model semisolid dosage forms containing the linden flower extract and to evaluate their quality by carrying out biopharmaceutical research. Objectives: 1. To analyse the scientific literature on the biological effect of Tilia cordata Mill. and on its application in the production of semisolid preparations. 2. To prepare a linden flower liquid extract and to evaluate its quality. 3. To model semisolid dosage forms containing linden flower liquid extract and to evaluate their quality by examining the pH value and rheological properties. 4. To evaluate how the release of active compounds is influenced by the selected gelling agents. 5. To select the semisolid dosage form with the best quality and to optimise its composition. Methods: the qualitative analysis of the liquid extract of linden flower was conducted spectrophotometrically by determining the total amount of phenolic compounds. Quantitative composition of the linden flower extract was analysed by using high performance liquid chromatography. The quality of gels was evaluated by measuring pH values, rheological properties and by testing the release of active compounds in vitro. The object of the study: the semisolid dosage forms with linden flower liquid extract. Results: during the study stabile gels with the linden flower extract were produced. Gels of hypromellose (5.77 ± 0.01) and of the mixture of poloxamer and hypromellose (6.57 ± 0.03) were characterised with pH values that were appropriate for dermatological products. In vitro release studies revealed that after the 6-hour release test, the maximum phenolic compound stream (1.98 ± 0.04 mg/cm2) and the total amount of active compounds (0.86 ± 0.06 μg/ml) were identified in the gel, containing two gelling agents – poloxamer and hypromellose. After optimising its composition, it was determined that the optimal gel composition was 1.20% of hypromellose, 20% of poloxamer, 20% of linden flower extract and 58.80% of purified water. Conclusions: in vitro release studies showed that the release kinetics of active compounds depended on the gelling agent and the viscosity of the semisolid dosage form. The insertion of hypromellose in the poloxamer gel resulted in the decrease of the pH value and viscosity. The decreased viscosity of gels caused the release of a larger amount of active compounds. Moreover, Hypromellose is useful when prolonged action of the active substance is needed