Semi-Solids Lab - Jan 26

Occlusion in Dermatological Preparations

  • 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.