Jejak Farmasi : Pharmaceutical Characteristics and Formulation Strategies of Topical Semisolids

Understanding Topical Vehicles: Gel, Cream, and Ointment

Oleh Tim Penulis

Have you ever wondered why some skin medicines disappear quickly while others feel greasy and stay on the skin? The answer lies in the formulation base. In pharmacy, gels, creams, and ointments are the three main types of semisolid preparations used to treat skin conditions. Choosing the right one depends on two main factors: how the drug needs to be released into the skin and how the product feels to the patient. This material breaks down the differences between these three forms, focusing on what they are made of (composition), how they feel (aesthetics), and how they help the medicine penetrate the skin (drug release).

Gel

Composition and Structure.

Gel is generally a clear, translucent semisolid preparation consisting of a liquid component distributed throughout an interlocking network or colloidal dispersion,. Gels typically possess a high water content. The structure can be single-phase (macromolecules dispersed without visible boundaries) or two-phase (consisting of groups of small, distinct particles, sometimes called magma or milk).

Aesthetics and Application.

Gels offer a cooling effect due to the slow evaporation of water from the skin,. They possess good spreading ability on the skin, do not inhibit the physiological function of hair, and are easily washed off with water.

Drug Release.

The release of active ingredients from gel is often easier compared to other semisolid forms because the gel has a strong capability to hydrate the stratum corneum (outer layer of the skin). This hydration causes the stratum corneum structure to swell and expand, allowing the active ingredients to easily penetrate deeper into the dermis.

Cream

Composition and Structure.

Cream is defined as a semisolid preparation that is an emulsion, often specifically defined as containing not less than 60% water. Creams are multi-phase systems consisting of a lipophilic (oil) phase and a hydrophilic (aqueous) phase.

Classification.

Creams are categorized into two main types

Oil-in-Water (O/W) or m/a.

In this type, the aqueous phase is the continuous external phase. These creams are advantageous because they are easily washable, non-sticky, non-residue forming, and feel cool.

Water-in-Oil (W/O) or a/m.

In this type, the lipophilic phase is the continuous external phase.

Stability and Preservation.

Due to the presence of the aqueous phase, creams require the addition of antimicrobial agents (preservatives) because water serves as a medium for microbial growth. Creams are susceptible to breakdown if the mixing system is disturbed, often due to changes in temperature or excessive changes in composition.

Effect

Creams are often used for their emollient (skin-softening) effects.

Ointment (Salep)

Composition and Classification.

Ointment is a semisolid preparation intended for topical application on the skin or mucous membranes. Ointment bases (vehicles) are broadly classified into four categories.

Hydrocarbon (Oleaginous) Bases. These bases are greasy, minimally absorbing water, and are designed to prolong the contact of the drug with the skin,. They act as a protective covering/occlusive barrier, and are difficult to wash off.

Absorption Bases. These can either form a W/O emulsion when mixed with water or are W/O emulsions already capable of incorporating additional aqueous solution.

Water-Washable Bases. These are O/W emulsions, commonly referred to as "cream," that are easily washed off the skin.

Water-Soluble Bases. These bases are composed of water-soluble constituents and are sometimes more accurately referred to as "gel".

Mechanism and Effect.

Salep provides a local therapeutic effect. When applied to the skin, the base influences skin permeability, allowing the dispersed drug to diffuse out and penetrate the targeted underlying layers of tissue. The desired effect of salep is often occlusive, which enhances drug penetration and provides an emollient effect.

Conclusion

In conclusion, while gels, creams, and ointments are all classified as semisolid preparations, they exhibit distinct physicochemical properties that dictate their specific therapeutic applications. Gels provide rapid drug release and high patient acceptability due to their non-greasy, cooling nature, making them ideal for acute inflammation or hairy areas. Creams, being emulsion-based, offer versatility as both emollients and effective delivery vehicles that are cosmetically elegant and washable. Conversely, ointments serve as potent occlusive barriers, maximizing drug absorption and providing hydration for chronic, dry, or scaly lesions. Therefore, the selection of the appropriate dosage form requires a careful balance between the physicochemical stability of the drug, the condition of the patient's skin, and the desired rate of therapeutic delivery.