Pharmaceutical Ointments and Creams
Overview and Definition of Ointments
Definition: Ointments are defined as greasy semisolid preparations designed specifically for external application to the skin or various mucous membranes.
System Identification: Within the context of drug delivery, they are categorized as a specific delivery system with unique advantages and limitations.
Primary Classifications: * Medicated Ointments: These contain pharmacologically active ingredients intended for therapeutic effects. * Non-medicated Ointments: These generally serve as vehicles (bases) for medicated substances or are used for their physical properties (e.g., as emollients or protectants).
Official Reference: These preparations are governed by standards such as the BA456B-789(C) designation.
Advantages and Limitations of Ointment Drug Delivery Systems
Advantages: * Application and Retention: They offer ease of application and remain on the applied site for extended periods, providing a persistent physical presence. * Lubricating and Emollient Properties: Ointments provide significant lubrication and act as emollients, softening the skin and reducing friction. * Prolonged Drug Action: Due to their occlusive nature and stay-on properties, they facilitate a longer duration of drug activity compared to more fluid preparations. * Hydrophobic Nature: Their water-repelling qualities make them particularly effective for use on mucosal surfaces where moisture may otherwise wash away a preparation.
Disadvantages: * Aesthetic and Practical Issues: They are inherently greasy and can be difficult to remove from the skin or surfaces. * Staining: There is a high risk of staining clothing or linens upon contact. * Application Constraints: They are generally considered unsuitable for exudating (weeping or oozing) sites as they can trap moisture and interfere with wound drainage. * Drug Release Limitations: Depending on the base chosen, the release rate of the drug from the ointment into the skin may be limited.
Detailed Classification and Properties of Ointment Bases (USP)
1. Oleaginous Bases (Hydrocarbon Bases): * Composition: Composed primarily of hydrocarbons, such as petrolatum and paraffin. * Water Content: Contains no water. * Ability to Absorb Water: No ability to absorb water. * Washability: Defined as not washable; they are difficult to remove with water alone. * Greasiness: Highly greasy. * Occlusiveness: High level of occlusiveness, providing a strong barrier that prevents moisture loss from the skin. * Drug Release: Generally exhibits poor drug release characteristics. * Uses/Examples: Used as emollients and protectants. Specific examples include White Petrolatum.
2. Absorption Bases: * Composition: A combination of a hydrocarbon base and an emulsifier. * Water Content: Can be anhydrous (no water) or may contain some water depending on the specific type. * Ability to Absorb Water: High; they have the capacity to incorporate aqueous solutions. * Washability: Not easily washable. * Greasiness: Yes, these are greasy preparations. * Occlusiveness: Moderate to high occlusiveness. * Drug Release: Better drug release potential than oleaginous bases. * Uses/Examples: Hydrophilic petrolatum, Lanolin, and commercial products like Aquaphor.
3. Emulsion Bases: * Composition: Consolidated from water and oil phases with an emulsifier. * Water Content: Contains significant water. * Ability to Absorb Water: Limited, depending on the specific emulsion type (Oil-in-Water or Water-in-Oil). * Washability: Easily washable (especially the Oil-in-Water types). * Greasiness: Less greasy than oleaginous or absorption bases, particularly Oil-in-Water (O/W) varieties. * Occlusiveness: Moderate occlusiveness. * Drug Release: Good drug release characteristics. * Uses/Examples: Moisturizing creams and lotions. Specific examples include Hydrophilic ointment and Eucerin.
4. Water-Soluble Bases: * Composition: Composed of materials like Polyethylene glycol (PEG). * Water Content: Normally contains none or minimal water. * Ability to Absorb Water: Yes, they can absorb water. * Washability: Easily washable. * Greasiness: Non-greasy. * Occlusiveness: None. * Drug Release: Excellent drug release characteristics, especially for solid therapeutic agents. * Uses/Examples: Water-soluble drug applications. Specific examples include and .
Preservatives and Formulation Safety
Common Preservatives Used: * Propylparaben * Methylparaben * Phenols
Primary Functions of Preservatives: * Microbial Prevention: They prevent microbial contamination of the product. * Shelf Life: They extend the formulation's shelf life by maintaining chemical and biological stability. * User Safety: They maintain product safety during repeated use, which is critical for consumer protection.
High-Risk Factors Requiring Preservation: * Water Content: Formulations containing water (like emulsion bases) provide an environment conducive to microbial growth. * Multi-dose Packaging: Preparations packaged in multi-dose containers are at high risk for contamination each time the container is opened and the product is accessed by the user.
Comparison: Ointments vs. Creams
Criteria for Differentiation: * Appearance: Ointments are typically more translucent and greasy, while creams are usually opaque and white. * Occlusiveness: Ointments are more occlusive than creams. * Water Content: Ointments have low to no water content; creams have higher water content. * Skin Penetration: Differences exist in how deeply each vehicle allows a drug to penetrate the skin layers. * Application Suitability: Ointments are better for dry, thick skin; creams are often preferred for moist or weeping lesions. * Ease of Spread: Creams generally spread more easily over large areas than ointments. * Cosmetic Acceptability: Creams are generally more cosmetically acceptable because they are less greasy and "vanish" upon rubbing. * Drug Release: The rate at which the medication is released from the vehicle into the skin varies between the two.
Questions & Discussion
Humor in Pharmaceutics: * Question: Why are ointments such good listeners? * Response: Because they absorb everything you say.