Definition of Semisolid dosage
Semisolid dosage forms are pharmaceutical preparations that have a consistency between that of liquids and solids.
They are typically applied topically to the skin or mucous membranes for localized or systemic effects.
Semisolid dosage forms offer several advantages, such as easy application, good patient compliance, and enhanced drug penetration through the skin or mucous membranes.
These dosage forms can be classified into several categories:
1. Ointments:
Ointments are viscous, greasy, and non-granular semisolid preparations, usually containing a high proportion of lipophilic components.
They are used for their emollient, protective, or occlusive effects and can also serve as drug delivery systems.
Ointments can be further classified based on their composition:
a. Oleaginous ointments:
These ointments contain hydrocarbon bases like petrolatum, which are water-insoluble and provide an occlusive barrier.
b. Absorption ointments:
These ointments contain an oleaginous base with added components, such as lanolin or beeswax, that can absorb water or aqueous solutions.
c. Water-removable ointments:
These ointments are oil-in-water emulsions that can be easily washed off the skin and are less greasy than oleaginous ointments.
d. Water-soluble ointments:
These ointments are composed of water-soluble bases like polyethylene glycols and do not contain any oil.
2. Creams:
Creams are semisolid preparations consisting of an emulsion of oil and water, either oil-in-water (O/W) or water-in-oil (W/O).
They have a more fluid consistency compared to ointments, and they spread easily on the skin. Creams are used for their emollient, moisturizing, or drug delivery properties.
3. Gels:
Gels are semisolid systems in which a liquid phase is immobilized by a three-dimensional network of a gelling agent.
Gels can be transparent, translucent, or opaque, and they may be aqueous-based (hydrogels) or non-aqueous-based (organogels).
They provide a cooling effect upon application and are often used for their lubricating, drug delivery, or cosmetic properties.
4. Pastes:
Pastes are semisolid preparations with a high proportion of solid components dispersed in an ointment base.
They have a stiff consistency and are less greasy than ointments. Pastes are used for their protective, occlusive, and drug delivery properties.
5. Lotions:
Lotions are liquid-to-semisolid emulsions or suspensions intended for topical application.
They have a more fluid consistency than creams, allowing them to be spread easily over a large surface area.
Lotions are used for their moisturizing, soothing, or drug delivery properties.