These free B.Pharm notes on gastrointestinal agents cover chapter 14 of Pharmaceutical Inorganic and Analytical Chemistry (BP106T), a first-semester subject. Read the key points below, then study the complete chapter PDF. You can browse every chapter in the Pharmaceutical Inorganic and Analytical Chemistry category.
Table of Contents
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Overview of gastrointestinal agents
These notes cover the inorganic agents that act on the gastrointestinal tract, starting with acidifiers such as sodium acid phosphate and dilute hydrochloric acid. They then explain gastric antacids, saline cathartics like milk of magnesia, and topical antimicrobials such as potassium permanganate, boric acid, hydrogen peroxide and chlorinated lime, ending with iodine and its preparations, including the assay, factor and uses of each compound.
Key points on gastrointestinal agents
- Acid-neutralising capacity (ANC) is the number of milliequivalents of HCl needed to keep 1.0 ml of an antacid suspension at pH 3 for 2 hours in vitro.
- Systemic antacids such as sodium bicarbonate are absorbed and may cause systemic alkalosis, while non-systemic antacids such as aluminium hydroxide gel are insoluble and poorly absorbed.
- Aluminium and calcium antacids cause constipation and magnesium antacids are laxative, so combinations such as Al(OH)3 gel with Mg(OH)2 balance these effects.
- Aluminium hydroxide gel is assayed by complexometric EDTA back titration with 0.05 M lead nitrate, using xylenol orange as indicator, with a yellow to red-purple end point.
- Hydrogen peroxide is assayed with 0.1 N KMnO4, which acts as its own indicator, and a 3 % solution is called 10 volume solution.
Relevance to pharmacy practice
Antacids, saline laxatives and topical antiseptics are among the most common inorganic medicines a pharmacist dispenses and checks. Knowing their assays, factors, doses and side-effects such as alkalosis, acid rebound or constipation helps in quality control and in advising patients safely.
Every chapter in this subject builds on the one before it, so do not skip topics that look simple. Definitions, principles, procedures and examples are the parts that examiners return to most often, and a clear understanding here will also make later subjects easier to follow in the coming semesters.
Frequently asked questions on gastrointestinal agents
What is the difference between systemic and non-systemic antacids?
Systemic antacids, such as sodium bicarbonate and sodium citrate, are absorbed into the blood and can cause systemic alkalosis. Non-systemic antacids, such as aluminium hydroxide gel and magnesium trisilicate, are insoluble, poorly absorbed and do not change blood acid-base balance.
What are the ideal properties of an antacid?
An ideal antacid neutralises at least 5 mEq per dose unit, raises gastric pH to 3.5 to 4.0 within 10 to 15 minutes, gives little gas, causes no alkalosis, acid rebound, constipation or diarrhoea, and is palatable and cheap.
How is boric acid assayed?
Boric acid is too weak to titrate directly, so it is dissolved in a neutralised mixture of water and glycerine, where it forms strong monobasic glyceroboric acid, which is titrated with 1 N NaOH using phenolphthalein.
Quick revision checklist
Use this self-test after reading the chapter on gastrointestinal agents. If you can do all of the following without looking at your notes, you are ready for the exam.
- I can explain: the three roles of gastric hydrochloric acid
- I can explain: systemic and non-systemic antacids with examples
- I can explain: the meaning of acid-neutralising capacity
- I can explain: how saline cathartics work by osmosis
- I can explain: the mechanisms of topical anti-infective agents
Study and exam tips
Start by reading the chapter once for the overall idea, then revise gastrointestinal agents using headings, definitions, principles, reactions and examples. Short-answer questions in the university exam usually ask for definitions, principles, procedures, reactions and uses, so write these in your own words and practise the equations, tables and flow charts that the chapter has.
For wider reading, standard books and open resources such as the NCBI Bookshelf help you confirm terms and see more examples. Revise gastrointestinal agents again a day later and again a week later, because spaced revision improves long-term memory.
This page is part of the Pharmaceutical Inorganic and Analytical Chemistry series for first-semester B.Pharm students on B.Pharm Guru, where every chapter has a short summary and a full PDF. Bookmark this page and share it with classmates who are preparing for the same exam.
Related notes: 16. EXPECTORANTS, 17. EMETICS.
Next: 15. RADIO PHARMACEUTICALS. Back to the Pharmaceutical Inorganic and Analytical Chemistry category.
