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DrX Whiz Niraj
Gastrointestinal Agents: Acidifiers
Comprehensive exam notes on GI Acidifiers. Understand Achlorhydria, Dilute HCl, and the complete Assay of Ammonium Chloride (*).
Gastrointestinal (GI) Agents are drugs used to treat gastrointestinal disorders (like acidity, constipation, or lack of gastric acid).
Acidifiers (also known as acidifying agents) are drugs or chemicals used to increase the acidity in the gastrointestinal tract, blood, or urine.
Why do we need Gastric Acidifiers?
The parietal cells of the stomach normally secrete Hydrochloric acid (HCl) to maintain a highly acidic pH (1.5 to 2.0). This acid is required to activate pepsin (for protein digestion) and kill harmful bacteria.
Sometimes, the stomach fails to produce enough acid. This leads to two conditions:
- Achlorhydria: Complete absence of free HCl in the stomach.
- Hypochlorhydria: Deficient (low) secretion of HCl in the stomach.
To treat these conditions, we use Gastric Acidifiers like Dilute Hydrochloric Acid.
Properties
- Formula: HCl
- Appearance: Colorless, strongly acidic liquid.
- Concentration: Dilute HCl contains exactly 10% w/w of Hydrogen Chloride.
Medicinal Uses
- Used as a Gastric Acidifier to treat achlorhydria and hypochlorhydria.
- Aids in the digestion of proteins by activating Pepsinogen into Pepsin.
Practical Alert: Dental Enamel Protection
Dilute HCl is highly corrosive to dental enamel (the outer protective layer of teeth). Therefore, when prescribed orally, it must be highly diluted with water (typically 100-200 times) and should be sipped through a glass or plastic straw so it does not touch the teeth.
Compounds marked with an asterisk (*) in the PCI syllabus require you to study their Preparation and Assay. Ammonium Chloride is a highly important compound.
Molecular Formula: NH₄Cl
Synonym: Sal ammoniac, Muriate of ammonia.
A. Preparation
It is prepared commercially by neutralizing Ammonia (NH₃) with Hydrochloric acid (HCl). The solution is then evaporated to obtain crystals of Ammonium Chloride.
B. Assay of Ammonium Chloride (Formol Titration)
The assay of Ammonium Chloride is performed by an indirect acid-base titration using Formaldehyde. This is known as Formol Titration.
Principle of Assay:
Ammonium chloride is a salt of a strong acid (HCl) and a weak base (NH₄OH). Direct titration with NaOH does not give a sharp end-point.
To solve this, Formaldehyde (HCHO) is added to the solution. Formaldehyde reacts with ammonium chloride to form a neutral compound called Hexamine (Hexamethylenetetramine) and water, and in the process, it releases free Hydrochloric Acid (HCl).
The liberated HCl is a strong acid, which can now be easily titrated against standard Sodium Hydroxide (NaOH) using Phenolphthalein as an indicator.
C. Medicinal Uses of NH₄Cl
- Systemic Acidifier: It is used intravenously to treat severe metabolic alkalosis (where blood pH is abnormally high). The liver converts NH₄⁺ into urea, releasing H⁺ ions that acidify the blood.
- Expectorant: Highly popular in cough syrups. It irritates the gastric mucosa slightly, which reflexively stimulates bronchial secretions, helping to cough out sputum.
- Mild Diuretic: It was historically used as a diuretic to increase urine output.