Development of a furosemide-containing expandable system for gastric retention.

More than 50 years ago, the first gastroretentive dosage forms came up. Since then, no practical and at the same time reliable gastroretentive system is available on market. A major obstacle in the development of novel gastroretentive systems is the lack of proper predictive test methods. In the present work, we aimed at developing and fully characterizing an expandable gastroretentive system containing furosemide as model drug. On the one hand, we used well-established in vitro tests for drug dissolution and gastroretentive properties (paddle apparatus, swelling characteristics). On the other hand, we used two novel models (dissolution stress test device, mechanical antrum model) to assess these properties under biorelevant conditions. Moreover, we performed an in vivo study under fed and fasted conditions that combined blood sampling and a high-resolution imaging technique (magnetic marker monitoring) to determine gastrointestinal location with the assessment of a pharmacodynamic endpoint (urinary sodium excretion). In vitro dissolution tests confirmed prolonged drug release over more than 8 h independent from pH and with slight pressure sensitivity. Swelling studies indicated good swelling behavior within 4 h along with medium gastroretentive properties as determined with the mechanical antrum model. In vivo imaging showed prolonged gastric residence time after fed compared to fasted administration (481 min vs 38 min). Comparison of geometric means of AUCo-tlast of the model drug confirmed this observation with 10 times higher value after fed administration. Urinary excretion of sodium well reflected the increased sodium-reuptake inhibition due to higher furosemide exposure under fed conditions. However, the poor performance after fasted intake of the system is in line with data from several other gastroretentive formulations. The present study highlighted the value of novel test methods during the development of gastroretentive formulations. Yet, a system with reproducible gastroretentive properties especially under fasted conditions has to be designed.

The influence of hydroxypropyl methylcellulose (HPMC) molecular weight, concentration and effect of food on in vivo erosion behavior of HPMC matrix tablets.

Four different hydrophilic matrix formulations based on hydroxypropyl methylcellulose (HPMC) were investigated for erosion properties in vivo. Three formulations contained a fixed amount of HPMC (40%) with varying proportions of two HPMC grades with different molecular weights (Methocel K100LV and K4M), and a fourth formulation contained a lower amount of the HPMC of lower molecular weight (20%). The effect of food on the in vivo erosion behavior was investigated on two formulations containing different contents of the same HPMC grade. The in vivo erosion behavior and gastrointestinal transit were investigated using magnetic marker monitoring (MMM). The in vitro and in vivo erosion-time profiles show that the erosion was strongly dependent on the composition of the formulation. The formulations containing a larger proportion of high molecular weight HPMC or higher content of HPMC exhibit relatively slower erosion rate and vice versa. In vivo erosion rates were significantly higher under postprandial administration as compared to fasted state administration. No rapid disintegration of any of the formulations (i.e. formulation failure that can potentially cause dose dumping) was observed.