BI-671800 is a potent and selective antagonist of the CRTh2 (chemoattractant receptor-homologous molecule expressed on Th2 cells) receptor. It is primarily investigated for its therapeutic potential in inflammatory diseases mediated by type 2 immune responses. The compound shows promise in the treatment of asthma, particularly eosinophilic asthma, by inhibiting the activation and migration of Th2 cells, eosinophils, and basophils that contribute to airway inflammation. It has also been studied in other allergic and inflammatory conditions such as allergic rhinitis, atopic dermatitis, and chronic obstructive pulmonary disease (COPD) with an allergic component. By blocking prostaglandin D2 signaling through the CRTh2 receptor, BI-671800 helps reduce key inflammatory pathways involved in these diseases. Clinical development has focused on oral formulations to provide systemic anti-inflammatory effects with potential for improved patient compliance compared to inhaled therapies.