DrX %20(1).png)
DrX Whiz Niraj
Pharmaceutical Powders: Types & Dilution
Master the concepts of Solid Dosage Forms! Learn about Dusting, Effervescent, Eutectic Mixtures, and Geometric Dilution.
Definition: In pharmaceutics, a powder is a solid dosage form containing a mixture of finely divided drugs and/or chemicals in a dry form, meant for internal or external use.
Advantages
- More stable than liquid dosage forms (longer shelf life).
- Rapid onset of action compared to tablets/capsules (because disintegration is not required; it dissolves quickly).
- Convenient for drugs to be given in large doses (1-5g).
- Easy to swallow for children and elderly when mixed in water.
Disadvantages
- Bitter, nauseating, or unpleasant-tasting drugs cannot be easily dispensed in powder form.
- Deliquescent and hygroscopic drugs cannot be dispensed directly as they absorb moisture and spoil.
- Inaccurate dosing if patients measure bulk powders with household spoons.
- Not suitable for drugs that get destroyed in the stomach (like Insulin).
Powders are broadly classified into Bulk Powders (supplied in a single large container) and Divided Powders (supplied in individual packed doses).
| Type of Powder | Description & Official Preparations |
|---|---|
| Bulk Powders for Internal Use | Dispensed in a wide-mouth container. Dose is measured by a teaspoon. E.g., Antacids, Laxatives (Eno). |
| Bulk Powders for External Use | Non-toxic powders applied locally. Include Dusting Powders, Snuffs, Dentifrices (Tooth powder), and Insufflations. |
| Simple Powder (Divided) | Contains only ONE active ingredient, wrapped in individual paper packets. E.g., Aspirin powder. |
| Compound Powder (Divided) | Contains TWO OR MORE active ingredients mixed together and divided into separate doses. E.g., APC (Aspirin, Paracetamol, Caffeine) powder. |
A. Dusting Powders
Meant for external application to the skin. They must be very fine (passed through sieve #85) to avoid local irritation.
Medical Dusting Powders: Used for fungal infections (e.g., Clotrimazole powder).
Surgical Dusting Powders: Must be strictly sterilized, used in deep wounds and body cavities.
B. Hygroscopic & Deliquescent
Hygroscopic Powders: Absorb moisture from the atmosphere but remain solid.
Deliquescent Powders: Absorb so much moisture that they dissolve and turn into a liquid solution! (e.g., Calcium chloride, NaOH pellets).
C. Efflorescent Powders
Crystalline powders that lose their water of crystallization when exposed to a dry atmosphere. They become powdery or wet-looking, causing weight changes. (e.g., Caffeine, Sodium sulphate decahydrate, Borax).
D. Effervescent Powders / Granules
These are specially formulated powders containing the active drug mixed with Sodium Bicarbonate, Citric Acid, and Tartaric Acid.
Mechanism: When added to water, the acids and the base react to release Carbon Dioxide (CO₂) gas. This effervescence (fizz) masks the bitter/salty taste of the drug and promotes fast absorption.
Why use a mix of Citric and Tartaric acid? Using only citric acid makes the powder too sticky. Using only tartaric acid makes the powder crumble easily. A mixture of both gives perfect granules!
A Eutectic Mixture is formed when two or more specific solid organic compounds are mixed together, and their melting point drops below room temperature, turning the solid powder into a liquid.
How to dispense Eutectic Mixtures?
If a doctor prescribes Menthol, Thymol, or Camphor together in a powder, the pharmacist cannot mix them directly, or they will turn into a liquid paste.
Solution: We use an Inert Adsorbent (like Magnesium Carbonate, Light Magnesium Oxide, or Kaolin). The reacting solids are mixed individually with the adsorbent first, and then lightly blended together. The adsorbent keeps the particles separated and dry.
When a very potent drug (e.g., 10 mg) needs to be mixed with a large quantity of diluent (e.g., 1000 mg lactose), direct mixing will result in an unequal distribution of the drug. To ensure uniform mixing, the Geometric Dilution technique is strictly followed.
Rule of Geometric Dilution:
1. Place the potent drug in the mortar.
2. Add an equal volume/weight of the diluent and mix thoroughly.
3. Now, add an amount of diluent equal to the total volume currently in the mortar.
4. Repeat the process of doubling the powder volume until all the diluent is mixed in.