Pharma gyan Pandit

SEMISOLID DOSAGE FORMS

Semisolid dosage forms include ointments, liniments, gels, suppositories, plasters, and plaques.

I.     CLASSIFICATION OF SEMISOLID DOSAGE FORMS

1.   Ointments 

Þ   ointments 

Þ   creams 

Þ   pastes 

2.   Gels 

3.   Liniments 

4.   Suppositories 

Þ   rectal suppositories 

Þ   vaginal suppositories

Þ   urethral suppositories 

5. Plasters

Þ   medicated plasters 

Þ   transdermal delivery systems

6. Plaques

II. CHARACTERISTICS OF SEMISOLID DOSAGE FORMS

OINTMENTS are semisolid preparations intended for external application to the skin or mucous membranes; usually, but not always, they contain medicinal substances.

The types of ointment bases used as vehicles (vehiculum, basis unguenti) are selected for optimum delivery of the drug. Ointment properties vary, since they are designed for specific use, ease of application, or extent of application.

Oleaginous bases are described as ointments, emulsion bases may be termed creams, and the forms containing large amounts of solids are termed pastes.

Ointment bases should be nonirritating, easily removable, nonstaining, stable, non-pH-dependent and widely compatible with a variety of medicaments. They are categorized into four classes:

1. Oleaginous bases: vegetable fixed oils:  olive oil, almond oil, sunflower oil; animal fats; minerals:Vaseline (vaselinum), and paraffin (hard paraffin, paraffinum solidum; liquid paraffin, paraffinum liquidum). Bases of this type are occlusive, nearly anhydrous and provide an optimum stability for medicaments.

2. Absorption bases: anhydrous lanolin (lanolinum anhydricum, sheep¢s wool fat). It contains not more than 0,25% of water. It is suitable whenever a large volume of aqueous solutions must be incorporated into the ointment. Lanolin (lanolinum)  – anhydrous lanolin is converted to lanolin by the addition of 30% water. It is good emollient and protectant.

3. Emulsion bases: most commonly used type of ointment bases. The oil phase is typically made up of Vaselinum and/or liquid petrolatum (Paraffinum liqidum).

4. Water-soluble bases – they are generally prepared of polyethylene glycol.

TYPES OF OINTMENTS:

1. Ointments are prepared of solid active ingredients (1–25%), finely powdered and then incorporated into the oleaginous base. According to the way of administration they can be: ointments for skin application (unguenta dermatica: 20–100 g), eye ointments (unguenta ophthalmica: 3–10 g), nose ointments (unguenta nasalia), etc.

2. Pastes contain powders dispersed in the vehicle in quantity more than 25%. They are usually stiffer, less greasy and more absorptive than ointments. Pastes adhere reasonably well to the skin and they are suited for application on and around moist lesions. Pastes are less macerating than ointments. They easily may be removed from the skin. They are divided into pastes for application on the skin (pastae dermaticae) and dental pastes (pastae dentifricae). An official paste is the Zinc Oxide paste.

3. Creams are similar to ointments but they contain a water phase (water, aromatic water, etc.). They are classified as:

Þ   cold creams with roughly dispersed water phase and cooling properties

Þ   emollient creams with finely dispersed water phase, which soften the skin.

4. GELS or jellies are semisolid dosage forms with high degree of clarity, ease of application and ease of removal and use. The active ingredients are incorporated into water-soluble bases. The gels often provide a faster release of drug substance as compared to creams and ointments. Gel formulations include ophthalmic preparations of pilocarpine, carbachol; topical preparations for burn therapy; anti-inflammatory treatment; treatment of acne, etc. Depending on their ingredients some gels may function as protective coatings. Gels are prepared in adhesive forms in order to increase the contact time of the active ingredients, e.g., topical dosage forms for aphthous stomatitis.