Diphenhydramine (12.5mg/5ml) + Ammonium Chloride (125mg/5ml) + Terpin Hydrate (7.5mg/5ml) + Sodium Citrate (55mg/5ml) (Medical Monograph)

Overview

A fixed-dose combination antitussive and expectorant syrup used for the symptomatic relief of dry, non-productive cough associated with upper respiratory tract infections, common cold, and allergic conditions. Diphenhydramine provides antihistaminic, antitussive, and sedative effects; Ammonium Chloride acts as an expectorant by irritating the gastric mucosa to stimulate respiratory tract secretions; Terpin Hydrate is a centrally-acting antitussive and mild expectorant; Sodium Citrate acts as an alkalizing agent and expectorant to loosen phlegm.

The combination works synergistically. Diphenhydramine antagonizes histamine at H1-receptors in the respiratory tract, reducing allergic cough and post-nasal drip. Its central anticholinergic action in the medulla suppresses the cough reflex. Ammonium Chloride produces irritation of the gastric mucosa, leading to a reflex increase in bronchial secretions via the vagus nerve, thinning the mucus (expectorant effect). Terpin Hydrate has a direct depressant effect on the cough center in the medulla oblongata and also stimulates respiratory tract secretions. Sodium Citrate, when absorbed, increases the alkalinity of respiratory tract secretions and blood, making the bronchial mucus less viscous and easier to expectorate.