Pharmaceutical Dosage Forms: Creams, Powders, and Solutions

Defining Creams and Pastes

Creams

Creams are semi-solid emulsions used externally on the skin. They can be either oil-in-water (O/W) or water-in-oil (W/O) emulsions. They are used for moisturizing, healing, or delivering drugs through the skin.

• Example: Cold Cream (W/O), Vanishing Cream (O/W)

Pastes

Pastes are also semi-solid but contain a high amount of insoluble powders (around 25-50%), making them stiffer and more absorptive. They form a protective layer on the skin and are used where longer contact is needed.

• Example: Zinc Oxide Paste

Understanding Pharmaceutical Aerosols

Aerosols are pressurized dosage forms that release active ingredients as a fine spray, mist, or foam when a valve is opened. They use propellants (like hydrocarbons or compressed gases) to expel the content. They provide quick and localized drug delivery, especially to the lungs or skin.

• Example: Asthalin Inhaler (for asthma), Spray deodorants

What Are Isotonic Solutions?

An isotonic solution is one that has the same osmotic pressure as body fluids (like blood, tears, or plasma). These solutions do not cause shrinking or swelling of cells. They are ideal for injections, eye drops, and nasal sprays to avoid irritation.

• Example: Normal Saline (0.9% NaCl solution)

Simple vs. Compound Powders

This table differentiates between simple and compound powders:

Two Key Advantages of Suspensions

1. Used for insoluble drugs: Drugs that are not soluble in water can be administered in suspension form.
2. Better taste masking: As the drug is not fully dissolved, its unpleasant taste is reduced.

Defining Pharmaceutical Lotions

Lotions are liquid topical preparations meant for external application without rubbing. They may be solutions, suspensions, or emulsions and are used to soothe, cool, or protect the skin. They are commonly used for sunburn, itching, and skin irritation.

• Example: Calamine Lotion

Preparing an Effervescent Powder

This section explains the preparation of an effervescent powder using Citric Acid, Tartaric Acid, and Sodium Bicarbonate.

Formula (in parts)

• Citric Acid – 1 part
• Tartaric Acid – 2 parts
• Sodium Bicarbonate – 3.4 parts

Method of Preparation

1. Dry all ingredients to remove moisture.
2. Mix all powders thoroughly in dry conditions.
3. Use light pressure to form the powder or compress it into granules.
4. Store in airtight containers.

On contact with water, the acid reacts with the bicarbonate to release carbon dioxide (CO₂), which produces effervescence (fizz) and makes the solution more palatable.

Defining and Classifying Powders

Definition

Powders are dry, finely divided solid dosage forms intended for internal or external use.

Classification

1. Dusting Powders: For external application (e.g., Prickly heat powder).
2. Internal Powders: For oral use (e.g., ORS powder).
3. Dentifrices: Used for cleaning teeth (e.g., Tooth powder).
4. Insufflations: Blown into body cavities (e.g., Nasal powders).

Formula and Preparation of Cold Cream

Cold Cream Formula

Method

1. Melt the waxes and oils together (this is the oil phase).
2. Dissolve the borax in warm water (this is the aqueous phase).
3. Add the aqueous phase slowly into the oil phase while stirring.
4. Stir continuously until the cream forms and cools.

Syrups and Elixirs Explained

Syrups

Syrups are sweet, viscous, concentrated solutions of sugar (like sucrose) with or without medicinal substances. They are used to mask a bitter taste and provide a pleasant flavor.

• Example: Paracetamol syrup

Elixirs

Elixirs are clear, sweetened hydro-alcoholic liquids containing drugs. They are more stable than syrups and may contain flavoring agents.

• Example: Cough Elixir (Diphenhydramine elixir)

Proper Handling of a Prescription

Steps

1. Receive the prescription from the patient.
2. Read and interpret the drug name, dose, and instructions carefully.
3. Check for potential drug interactions or contraindications.
4. Prepare the medication using accurate measurement and technique.
5. Label the medicine with the proper instructions.
6. Explain to the patient how to use it, including dosage, timing, and storage.

Example

Rx: Tab Amoxicillin 500mg
Sig: 1 tablet three times a day after food for 5 days

Effervescent Granules: Preparation and Examples

Effervescent granules are solid dosage forms that release CO₂ when dissolved in water, creating a fizzing effect.

Preparation

1. Ingredients: Citric acid, Tartaric acid, Sodium bicarbonate.
2. Sieve all powders and dry them if needed.
3. Add a small amount of ethanol or water to form a damp mass.
4. Pass the mass through a sieve to form granules.
5. Dry the granules and store them in an airtight container.

Two Official Preparations

1. Effervescent Sodium Bicarbonate
2. Effervescent Magnesium Citrate Granules

Methods for Preparing Emulsions

An emulsion is a biphasic liquid dosage form made by mixing two immiscible liquids using an emulsifying agent.

Methods

1. Dry Gum Method (Continental): Mix oil with gum (in a 4:1 ratio), then add water all at once while triturating quickly to form a primary emulsion.
2. Wet Gum Method (English): Mix gum with water first, then add oil slowly with continuous trituration.
3. Bottle Method: Used for volatile oils. Mix the oil and gum in a bottle, shake well, and then add the water.
4. Nascent Soap Method (Chemical method): The emulsifying agent (soap) is formed during preparation by a reaction between a fatty acid and an alkali. For example, Olive oil + Lime water.