Semisolid Dosage Forms

Definition of Semisolid Dosage Forms

• Semisolid Dosage Forms are pharmaceutical preparations intended for external application to the skin or mucous membranes, having a consistency between solid and liquid.
• They are used for both local and systemic effects.
• These forms provide a medium for the drug to be delivered to the site of action, and their formulation enhances absorption, stability, and patient compliance.

Classification of Semisolid Dosage Forms

Semisolid dosage forms are commonly classified into the following categories:

1. Ointments

• Ointments are greasy semisolid preparations meant for external application on the skin or mucous membranes.
• They have an oily base, making them suitable for use on dry and scaly skin.

• Types of Ointments:

  1. Hydrocarbon bases (e.g., Vaseline): Occlusive and emollient.
  2. Absorption bases (e.g., lanolin): Allows incorporation of aqueous solutions.
  3. Water-removable bases (e.g., hydrophilic ointment): Easily washed off.
  4. Water-soluble bases (e.g., polyethylene glycol ointment): Non-greasy and easily washable.

2. Creams

• Creams are emulsions of oil and water, typically more viscous than lotions.
• They are designed to be easily spreadable and less greasy than ointments.

• Types of Creams:

  1. Oil-in-water (O/W) creams: These have water as the external phase and are washable with water (e.g., moisturizing creams).
  2. Water-in-oil (W/O) creams: These have oil as the external phase and provide a more occlusive layer than O/W creams.

3. Gels

• Gels are semisolid systems consisting of large molecules or small inorganic particles dispersed in a liquid.
• They are usually transparent and non-greasy.

• Types of Gels:

  1. Hydrogels: Water-based gels.
  2. Organogels: Non-aqueous gels, often using organic solvents.
  3. Gels have good penetration and are suitable for both local and systemic drug delivery.

4. Pastes

• Pastes are thick, stiff semisolid preparations containing a high percentage of finely powdered substances, which make them less greasy and more absorptive than ointments.
• They are intended for application to areas that require protection or drying effects.
• Examples: Zinc oxide paste used for skin conditions.

5. Lotions

• Lotions are fluid suspensions or emulsions, typically less viscous than creams.
• They are applied over large areas of the skin and evaporate quickly, leaving behind a thin layer of medication.
• Example: Calamine lotion.

6. Plasters

• Plasters are solid or semisolid adhesive masses spread onto a backing material like fabric or paper.
• They are used to provide support or protection to the skin.

7. Foams

• Foams are dispersions of gas in a liquid or semisolid base.
• They are lightweight, easy to apply, and spread well over large areas of the skin.

8. Suppositories (Semisolid for Rectal/Vaginal Use)

• Suppositories are solid at room temperature but become semisolid or liquid when inserted into the body.
• They are used for rectal or vaginal administration.

Characteristics of Semisolid Dosage Forms:

1. Spreadability: Ease of application and distribution over the skin.
2. Viscosity: Affects the flow and retention on the application site.
3. Occlusiveness: The ability to form a barrier on the skin that prevents water loss.
4. Absorbability: The degree to which the skin absorbs the preparation.

Click Here to Watch the Best Pharma Videos!