Semisolid Dosages: Ointments, Creams, and Gels

SEMISOLID DOSAGES: OINTMENTS, CREAMS, AND GELS

Introduction

  • Ointments, creams, and gels are semisolid dosage forms designed for topical application.

  • Possible routes of application include skin, eyes, nasal passages, vagina, or rectum.

  • These forms can be medicated or serve as protectants/lubricants.

Classification of Ointment Bases

  1. Oleaginous bases

  2. Absorption bases

  3. Water-removable bases

  4. Water-soluble bases

Oleaginous Bases

  • These are hydrocarbons and include:

    • Petrolatum, USP:

      • Purified mixture of semisolid hydrocarbons from petroleum.

      • Thick mass; melts at 38°C to 60°C.

      • Also known as yellow petrolatum or petroleum jelly.

    • White Petrolatum, USP:

      • Purified, decolorized mixture; more visually appealing.

      • Used similarly to petrolatum; available as White Vaseline.

    • Yellow Ointment, USP:

      • Composition: Yellow wax (50g) + Petrolatum (950g).

      • Prepared by melting yellow wax and mixing with petrolatum.

    • White Ointment, USP:

      • Substitutes white wax and white petrolatum for yellow variants.

      • Provides moisture, occlusion, and lasting application on skin.

Absorption Bases

  • These bases allow incorporation of aqueous solutions:

    • Types:

      • 1. Bases that create W/O emulsions (e.g., hydrophilic petrolatum).

      • 2. W/O emulsions allowing incorporation of more water (e.g., lanolin).

    • Not easily washed off, useful for incorporating small volumes of aqueous solutions.

    • Hydrophilic Petrolatum Layout:

      • Ingredients: Cholesterol (30g), Stearyl alcohol (30g), White wax (80g), White petrolatum (860g).

    • Lanolin, USP:

      • Sourced from sheep wool; contains ≤0.25% water.

      • Can incorporate additional water when mixed.

Water-removable Bases

  • Oil-in-water emulsions resembling creams.

  • Easily washed off; can absorb serous discharges.

  • Hydrophilic Ointment, USP:

    • Formula: Methylparaben (0.25g), Propylparaben (0.15g), Sodium lauryl sulfate (10.00g),
      Propylene glycol (120.00g), Stearyl alcohol (250.00g), White petrolatum (250.00g), Purified water (370.00g).

  • Preparation involves melting stearyl alcohol and white petrolatum, adding other agents until congealed.

Water-soluble Bases

  • Do not contain oleaginous components; completely water washable.

  • Used primarily for solid substance incorporation.

    • Polyethylene Glycol Ointment, NF:

    • A polymer represented by formula H(OCH2CH2)nOH, where n varies.

    • Different PEG molecular weights alter physical properties.

    • Custom formulations can adjust firmness or incorporate aqueous solutions.

Selection of the Appropriate Base

Aspects to consider:

  1. Desired drug release rate.

  2. Topical absorption.

  3. Occlusion effect.

  4. Drug stability and interaction.

  5. Washability from skin.

  6. Type of skin condition:

    • Ointments suitable for dry skin.

    • Creams for weeping surfaces.

    • Lotions for intertriginous areas.

Additives
Preservatives

  • Essential for microbial resistance, particularly in aqueous preparations.

    • Commonly used: Methyl/Propyl hydroxy benzoate, Benzoic acid, Quaternary ammonium substances.

Antioxidants

  • Prevent degradation via free radicals.

    • Example: Butylated hydroxy anisole (BHA).

Humectants

  • Hygroscopic substances that enhance moisture retention and solubility of actives.

Preparation of Ointments

  • Methods depend on ingredient nature:

    1. Levigation: Incorporation of fine solids.

    2. Fusion: Melting components together before cooling.

  • Large-scale production involves milling, mixing, and emulsification tools.

  • Sterility for ophthalmic use is crucial; includes aseptic handling.

Evaluation

  • Characteristics like physicochemical properties, microbial content, and packaging must be assessed.

  • Assay: Measuring drug content using various analytical methods (e.g., chromatographic).

  • In vivo studies to establish drug bioavailability.

  • Microbial testing to ensure product safety, especially for ophthalmics.

Packaging, Storage, and Labeling

  • Use large-mouth jars or metal/plastic tubes.

  • Store in cool, dark places to maintain integrity.

Creams

  • Creams are less greasy due to water content, allowing for easier application and removal.

Gels

  • Gels contain liquid interspersed with particles, suitable for various application routes.

  • Gels show characteristics such as imbibition, swelling, and thixotropy, affecting delivery.

  • Types include hydrogels (water-soluble) and organogels (oleaginous saturates).

Miscellaneous Semisolid Preparations

  1. Pastes: High solid content; used for absorbing secretions.

  2. Plasters: Adhesive masses for localized drug delivery.

  3. Glycerogelatins: Mixes for treating skin conditions like ulcers.