Behind every pill, powder, or syrup lies a world of precision, science, and technique. Pharmacists are not merely dispensers of medicines—they are the custodians of accuracy. From ensuring the correct strength of a solution to designing stable and effective dosage forms, their expertise safeguards patient health. Unit 2 of Pharmaceutical Sciences introduces students to pharmaceutical calculations, powders, and liquid dosage forms, laying the groundwork for professional practice.
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Pharmaceutical Calculations: The Language of Accuracy
Weights and Measures – Imperial & Metric Systems
Pharmacy, at its core, relies on exact measurement. Historically, the Imperial system was widely used, where units like grains, ounces, and pints dominated pharmaceutical calculations. However, with globalization and scientific advancement, the Metric system—based on grams, liters, and meters—has become the universal standard for drug formulation and dispensing.
Today, pharmacy students must be fluent in both systems, as prescriptions, literature, and patient instructions may involve either. Mastery ensures there is no room for error when converting, preparing, or compounding medicines.
Calculations with Solutions and Concentrations
Pharmacists often prepare percentage solutions—whether weight/volume (w/v), weight/weight (w/w), or volume/volume (v/v). A simple error in concentration can mean the difference between a therapeutic drug and a toxic one.
The alligation method remains a handy tool for mixing solutions of different strengths to achieve a desired concentration. Similarly, proof spirit calculations are essential in formulations involving alcohol, as in tinctures and elixirs.
Isotonic Solutions – Comfort in Every Drop
When preparing eye drops or injections, isotonicity becomes critical. Solutions must match the osmotic pressure of body fluids to prevent irritation or damage. Pharmacists calculate isotonic solutions using freezing point depression and molecular weight concepts, ensuring patient comfort and safety.
Powders: The Oldest Yet Reliable Dosage Form
Definition and Classification
Powders, one of the oldest dosage forms, are finely divided solid drugs used for internal or external application. They may be simple (containing a single drug) or compound (a mixture of several ingredients).
Advantages and Disadvantages
Powders offer several benefits—they are stable, easy to swallow when mixed with food, and ideal for large doses. On the flip side, they may be less convenient to carry, have unpleasant taste, and are unsuitable for drugs sensitive to air or moisture.
Official Preparations and Special Categories
Dusting Powders: Used externally for wounds or skin irritation, providing soothing effects.
Effervescent Powders: Contain acid and carbonate/bicarbonate that release carbon dioxide when mixed with water, making the medicine more palatable.
Efflorescent Powders: Substances that lose water of crystallization, risking clumping or instability.
Hygroscopic Powders: Readily absorb moisture from the air, requiring careful packaging.
Eutectic Mixtures: Certain powders like camphor and menthol liquefy when mixed due to mutual solubility. Pharmacists use absorbents to manage such combinations.
Geometric Dilution – Mixing with Precision
When potent drugs are combined with diluents, uniform distribution is vital. The technique of geometric dilution—mixing equal portions of drug and diluent step by step—ensures that even the smallest dose delivers consistent therapeutic effect.
Liquid Dosage Forms: Medicines in Motion
Advantages and Disadvantages
Liquid dosage forms, such as syrups, elixirs, and suspensions, remain highly popular. Their key advantage lies in ease of administration, especially for children and elderly patients. Liquids also allow flexible dosing and faster absorption compared to solids.
However, they are bulkier to store, prone to microbial growth, and less stable than solid preparations. These challenges demand careful formulation and preservation techniques.
Excipients – The Unsung Heroes
Beyond the active drug, liquids contain excipients that improve stability, taste, and appearance.
Solvents such as water, alcohol, or glycerin dissolve the drug.
Preservatives like parabens and benzoic acid prevent microbial contamination.
Sweeteners (sucrose, sorbitol) and flavoring agents enhance palatability.
Viscosity enhancers (like carboxymethyl cellulose) improve mouthfeel and suspension stability.
Every excipient plays a strategic role, ensuring that the medicine is not only effective but also acceptable to the patient.
Solubility Enhancement Techniques
One of the biggest hurdles in liquid formulations is poor drug solubility. Pharmacists employ various strategies to overcome this:
Use of co-solvents (alcohol, propylene glycol) to increase solubility.
Salt formation to make drugs more water-soluble.
Complexation techniques using cyclodextrins to trap poorly soluble drugs.
Micronization and surfactant addition to improve dispersion and absorption.
These techniques reflect the pharmacist’s ingenuity in turning challenging drugs into patient-friendly solutions.