Diphenhydramine (10mg/5ml) + Ammonium Chloride (100mg/5ml) + Sodium Citrate (60mg/5ml) (Medical Monograph)

Overview

A fixed-dose combination antitussive and expectorant syrup. Diphenhydramine is a first-generation ethanolamine-class antihistamine with potent anticholinergic and sedative properties, providing cough suppression via central action on the medullary cough center. Ammonium Chloride acts as an expectorant by irritating the gastric mucosa, leading to a reflex increase in respiratory tract secretions, thereby reducing sputum viscosity. Sodium Citrate acts as an alkalizing agent and systemic expectorant, increasing the pH of respiratory secretions and bronchial fluid, making them less viscous and easier to expel. This combination is primarily indicated for the symptomatic relief of dry, non-productive cough associated with upper respiratory tract infections, common cold, and allergic conditions.

The combination works via three distinct mechanisms. 1) Diphenhydramine suppresses cough by a central action, depressing the cough center in the medulla oblongata. Its antihistaminic action also helps alleviate allergic components of cough. 2) Ammonium Chloride acts as a nauseant expectorant. After oral administration, it causes mild irritation of the gastric mucosa, which stimulates the vagal afferent nerves. This triggers a reflex via the medullary centers to increase the output of fluid by the bronchial glands, thereby thinning tenacious mucus. 3) Sodium Citrate, when absorbed, is metabolized to sodium bicarbonate, alkalinizing the blood and respiratory tract secretions. This change in pH reduces the viscosity of bronchial secretions, facilitating their removal.