About Loratadine Second Generation H1 Antagonist, Antihistamine. Mechanism of Action of Loratadine Loratadine blocks one type of receptor for histamine (the H1 receptor) and thus prevents activation (activation releasing other chemicals which produce the symptoms associated with allergy) of cells by histamine. Drug also has mast cell stabilizing property. Interactions for Loratadine Macrolide antibiotics, ketoconazole, cimetidine, ranitidine and theophylline: Caution should be exerted while co-administration of these drugs which are known to inhibit hepatic metabolism. About Pseudoephedrine Alpha/Beta Adrenergic Agonist, a phenethylamine derivative, A nasal decongestant. Mechanism of Action of Pseudoephedrine It is a nasal decongestant with alpha-2 agonistic action. It produces local vasoconstriction, reduces blood flow, and causes shrinkage of mucosa which provides relief of nasal congestion. It reduces oedema of the nasal mucosa, thus improving ventilation, drainage and nasa