Definition of Occlusion: Occlusion refers to the creation of a barrier over the skin. This barrier comes from the application of ointments or creams, particularly those that are oil-based. The primary purpose of occlusion is to prevent moisture loss from the skin.
Impact of Occlusion:
More occlusion = better barrier = reduced evaporation of moisture.
The stability of the drug in its base must be assessed prior to application; unstable drugs should not be used.
Other factors to consider for base selection include:
Effect of the drug on the consistency of the final formulation.
The nature of the formulation must be consistent for effectiveness.
Whether the formulation needs to be easily removable with water.
Characteristics of the surface where the preparation will be applied, influencing the choice between gels or water-soluble bases.
Guideline for Base Selection
Formulation Characteristics:
For faster drug release and more washable bases, oil-in-water emulsions are preferred. Example: Water-soluble bases feel non-greasy and can be easily washed away.
Moderate Occlusion: For a moderately occlusive effect, a water and oil emulsion can be used to create a moisture-retaining layer. Examples include:
Cold creams used for moisture retention.
Considerations for Sensitive Drugs:
Moisture-sensitive drugs may degrade in the presence of water and should be formulated using an anhydrous base (e.g., anhydrous lanolin).
Highly occlusive substances, like white petrolatum, provide maximum skin protection and moisture retention. Removal of such occlusive layers results in potential moisture loss.
Creams
Definition of Creams: Creams are semi-solid preparations that contain medicinal agents either dissolved or dispersed in water-oil or oil-water emulsions, or they may be water-soluble bases.
Usage of Creams:
Common for topical applications as well as rectal and vaginal uses.
Preferred over ointments due to easier application, spreadability, and removability.
Key Differences Between Creams and Ointments:
Creams have higher water content, while ointments have higher oil content.
Ointments are more viscous, greasy, and harder to spread due to the higher oil content, while creams have lower viscosity and are more easily spread.
Occlusiveness: Ointments are more occlusive because of higher oil content. Creams, having more water, have moderate occlusiveness and can be washed off easily.
Ointments
Definition: Ointments are semi-solid preparations with a higher oil composition than creams, leading to a greasy feel on the skin.
Occlusiveness: Ointments provide a strong occlusive effect due to high oil content, suitable for maintaining moisture in certain skin conditions.
Gels
Definition: Gels are semi-solid substances where the liquid phase is immobilized in a three-dimensional network created by a gelling agent.
Gelling Agent: In most cases, a gelling agent (e.g., carbomer) is required which, when neutralized, forms the gel.
Concentration of Carbomer: Usually 0.2% to 2.5%. Gels can be aqueous, hydroalcoholic, or anhydrous, although aqueous is most common.
pH Sensitivity: Carbomers are pH-sensitive and gel formation occurs in neutral or alkaline pH. Trolamine (triethanolamine) is added to adjust the pH for gelling.
Handling: Carbomer is hygroscopic and should be worked with quickly to prevent moisture absorption from the atmosphere.
Practical Applications for Tomorrow's Lab
Formulations:
Cream Preparations: Prepare a Pyroxicam 1% topical cream, substituting lactose monohydrate as the active ingredient. Include propylene glycol and an emollient cream based on the straightforward formula.
Ointment Preparation: Create a benzoyl peroxide 4.9% ointment using lactose monohydrate.
Gel Preparation: Make a 1.5% carbomer gel using isopropyl alcohol, ensuring the use of proper gelatinization techniques.
Mixing Techniques
Geometric Dilution: Employed to mix powders uniformly in formulations, ensuring equal portions are mixed incrementally.
Heating Methods: When melting bases, maintain a temperature around 75 degrees Celsius to avoid burning.
Dental Labeling: Ensure the final product looks neat and professional by smoothing the top and cleaning any excess before applying labels.
Final Notes
Compounding Records: Fill out compounding records for each lab formulation.
Questions: Review any uncertainties regarding formulations, measurements, or procedures before commencing the laboratory work.