Comprehensive Study Notes on Topical Dosage Forms and Ointment Bases

Pharmaceutical preparations can be administered via various routes including ophthalmic (eye), otic (ear), nasal, and oral/buccal (cheek).
Suppositories are also a common delivery method.
Isotonicity is a critical concept for products entering systemic circulation or the eye to ensure the product does not hydrate or dehydrate the surrounding cells.
Isotonic conditions maintain an equal osmotic pressure between the medium and the surrounding tissues or cells.
Osmosis involves the movement of water from high concentration to low concentration through a semi-permeable membrane.
A semi-permeable membrane is a necessary condition for osmosis, ensuring water passes freely between the cell and its surrounding environment to reach equal concentration balance.

Topical products are applied to the skin, excluding the mucosa, although some may reach mucosal surfaces.
The topical market represents approximately $10\%$ of all sales in the United States.
The compounding market for the skin is significantly larger, accounting for roughly $48\%$ of compounding activities.
Common applications of topical forms include over-the-counter (OTC) products and cosmetics.
Aesthetics and ideal characteristics for topical products include:
- Being visually attractive (especially foundations).
- Possessing a nice color.
- Not staining clothing.
- Ease of washing after application (though some oil-based products remain difficult to remove).

The skin consists of a top layer that must be breached for systemic drug delivery.
The dermis layer contains nerves and blood vessels. For a drug to enter systemic circulation, it must pass across the top layer (stratum corneum) and the dermis.
Transdermal drug delivery systems provide targeted delivery to systemic circulation.
Flux is the term used to describe the controlled delivery rate of a drug, such as a patch delivering $25\,\mu g/hr$ .
Skin enhancers, which can be physical or chemical, are used to facilitate the crossing of the skin barriers.
Low molecular weight molecules are generally required to penetrate the skin layers effectively.

Ointments are semi-solid preparations for external use that can serve as protectants, emollients, lubricants, or vehicles for medication.
There are four primary categories of ointment bases:
- Hydrocarbon Bases (Oleaginous Bases): These are occlusive in nature, meaning they seal the skin to hydrate it by preventing water evaporation. They are greasy and have a mounting (melting) point between $38^{\circ}C$ and $60^{\circ}C$ . Examples include White Petrolatum (Vaseline) and Mineral Oil.
- Absorption Bases: These permit the incorporation of aqueous solutions, resulting in water-in-oil (W/O) emulsions. They are greasy but can absorb water. Examples include Aquaphor, Aquabase, and anhydrous lanolin (obtained from the wool of sheep).
- Water-Removable Bases: These are oil-in-water (O/W) emulsions known as "washable bases" because they are easy to remove with water. Ingredients often include stearyl alcohol, white petrolatum, sodium lauryl sulfate, and preservatives such as parabens. Examples include Hydrophilic Ointment, Cetaphil, Unibase, and Vernibase.
- Water-Soluble Bases: These are non-occlusive and dehydrate the skin. They contain no petrolatum and are made primarily of Polyethylene Glycol (PEG), also known as Macrogol. PEG $400$ is a low molecular weight liquid, while higher molecular weights like PEG $3350$ are waxy. Examples include PEG Ointment.

Gels: These require a gelling agent to create viscosity. A characteristic of a good gel is the "snap" or structured consistency. pH adjustment is often essential for the gel to set up properly. Mixing should be done with low shear to avoid trapping air bubbles.
Pastes: Pastes are similar to ointments but contain a much higher percentage of solids. This makes them stiffer and more protective. An example is Zinc Oxide paste, which contains $40\%$ solids.
Creams: Creams are semi-solids with lower viscosity than ointments. They can be water-in-oil or oil-in-water emulsions. Because they contain water, they require preservatives like parabens to prevent bacterial growth. Examples include Hydrocortisone and Clotrimazole ( $1\%\text{ cream}$ ).

Lotions: These are liquid preparations intended for external use, providing more fluidity than creams. They consist of $30\%$ to $80\%$ water and $35\%$ to $25\%$ oil.
- Formulation: Includes emulsifying agents ( $1\%$ to $10\%$ ), humectants (like glycerin or propylene glycol), and thickeners (like carbomers).
- Examples: Calamine lotion and Capsaicin lotion (used for redness and vasodilation).
Collodions: These are clear or slightly opalescent syrupy liquids composed of pyroxylin dissolved in a mixture of ether and alcohol. When applied, they form a protective film. An example is Salicylic Acid collodion used for corn and callus removal.
Plasters: These are solid or semi-solid materials that provide medical support for broken bones or skin protection.

Incorporation: This involve mechanical mixing, often using a spatula and tile or a mortar and pestle to grind solids into fine particles before mixing them into the base.
Fusion: This method uses heat to melt components together. The bases are melted, and other ingredients are added while in a liquid state. The mixture is then cooled while stirring until it congeals.

The discussion touched upon the difficulty of washing away oil-based foundations and the importance of aesthetic color in topical formulations.
A conversation occurred regarding a student named Logan who is proficient in heart physiology; the participants discussed walking together to review physiology concepts.
Personal context was shared regarding current classes, where Patient Care Lab is noted as easy for those working in pharmacies, but subjects like pharmaceutics and titration may be more challenging.
An anecdote was shared about a persistent craving for cupcakes and looking for a specific bakery.
There was a note that pharmaceutical solution discussions would continue in a subsequent session.