cetirizine + cholecalciferol

**Cetirizine + cholecalciferol** is a non-standardized combination of two active substances: cetirizine, an oral second-generation antihistamine that acts mainly as a selective antagonist at the histamine H1 receptor, and cholecalciferol, also known as vitamin D3, a secosteroid hormone involved in calcium and phosphate homeostasis and bone metabolism. There is limited but emerging clinical evidence that the combination (administered as topical cetirizine plus oral cholecalciferol or both orally) can be used for conditions such as congenital hypotrichosis and allergic rhinitis, especially in patients with vitamin D deficiency[2][5][6].\n\nIn this combination:\n- **Cetirizine** blocks the action of endogenous histamine at the H1 receptor to prevent allergic symptoms such as itching, sneezing, and runny nose.\n- **Cholecalciferol (vitamin D3)** raises serum levels of vitamin D, potentially modulating immune response and inflammation.\n\nThere are no widely recognized proprietary combination products using both active ingredients under a single brand name, and both substances are most often co-administered in clinical practice based on specific therapeutic needs rather than as a fixed-dose combination.