Ointments

These flashcards cover key concepts related to ointments, their types, components, functions, and related chemical processes.

Ointment

A semi-solid dosage form, usually anhydrous with a hydrophobic oily base, intended for external application to the skin or mucous membrane.

Hydrophobic Ointment

Ointments that absorb only small amounts of water, providing an occlusive effect intended for emollient or protective purposes.

Hydrophilic Ointment

Preparations that are miscible with water and skin secretions, offering less emollience.

Emollient

Substance that softens and moisturizes the skin, suitable for dry skin.

Chemical Penetration Enhancer (CPE)

A substance included in a formulation to enhance drug penetration across biological barriers without the need for auxiliary equipment.

Antioxidant

Substance that prevents rancidification of formulation components and terminates free-radical chain reactions.

Free Radical

An atom or molecule that has unpaired electrons, making it highly reactive and potentially damaging to cells.

Lipophilic Drugs

Drugs that have a high affinity for lipids or fats.

Water-Emulsifying Ointment

Ointments that can absorb larger amounts of water and form either water-in-oil or oil-in-water emulsions.

Permeability Coefficient

A measure predicting the ability of a drug to penetrate a biological barrier based on its molecular weight and partition coefficient.

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What is an ointment according to the British Pharmacopoeia?

A single-phase semi-solid preparation in which solids or liquids may be dispersed; bases may be hydrophobic water-emulsifying or hydrophilic

What is the usual nature of an ointment base?

Anhydrous and hydrophobic

Why are ointments suitable for dry skin?

They are emollient and occlusive reducing transepidermal water loss

How does occlusion enhance drug delivery?

By increasing skin hydration and enhancing dermal drug penetration

What are the three main types of ointments?

Hydrophobic water-emulsifying and hydrophilic ointments

What characterises hydrophobic ointments?

Occlusive greasy not water-washable absorb little water

Give examples of hydrophobic ointment bases

White soft paraffin liquid paraffin petrolatum

What are water-emulsifying W/O ointments?

Absorption bases that form water-in-oil emulsions with skin secretions

Key excipient used in W/O ointments?

Lanolin and its derivatives

What are water-removable O/W ointments?

Form oil-in-water emulsions and are water-washable

Examples of O/W emulsifying excipients?

Cetostearyl alcohol cetomacrogol

What characterises hydrophilic ointments?

Water-miscible non-greasy water-washable

Example of a hydrophilic ointment base?

Macrogols polyethylene glycols

What are the basic components of an ointment?

Drug and ointment base

Why are preservatives usually unnecessary in ointments?

Lack of water limits microbial growth

Role of solvents in ointments?

Dissolve drug or excipients and must be miscible with the base

When are emulsifying agents required in ointments?

In water-emulsifying ointments

How can drugs be incorporated into ointments?

Dissolution in base dissolution in solvent then incorporation or levigation

What is levigation?

Grinding a solid drug with a small amount of liquid to form a smooth dispersion

Why is geometric dilution used?

To ensure uniform drug distribution

What is rancidification?

Oxidative free-radical chain reaction degrading fats and oils

Why are antioxidants added to ointments?

To prevent oxidative degradation of formulation components

How do antioxidants work?

Sacrificial donation of electrons to terminate free-radical chain reactions

Key requirement for antioxidants in ointments?

They must be soluble in the ointment base

Examples of antioxidants used in ointments?

Vitamin E BHT BHA propyl gallate

What is a chemical penetration enhancer CPE?

An excipient that increases drug penetration across the skin

Advantage of chemical over physical penetration enhancement?

No auxiliary equipment required

Examples of physical penetration enhancement methods?

Microneedles iontophoresis electroporation sonophoresis

Ideal molecular weight for percutaneous drug delivery?

Less than 500 Da

Ideal lipophilicity range for skin penetration?

Log P approximately 1 to 4

Ideal daily dose for transdermal delivery?

Less than 10 mg per day

Two main ways CPEs increase drug permeability?

Increase drug partitioning K and diffusivity D

Main barrier to percutaneous drug absorption?

Stratum corneum

How do CPEs affect stratum corneum lipids?

Disrupt lipid packing increasing diffusivity of lipophilic drugs

How do CPEs affect stratum corneum proteins?

Alter proteins increasing diffusivity of hydrophilic drugs

How do CPEs enhance partitioning?

Increase drug transfer from formulation into skin

Examples of alcohol penetration enhancers?

Ethanol isopropanol propylene glycol

Examples of terpene penetration enhancers?

Menthol limonene eucalyptol

Examples of fatty acid penetration enhancers?

Oleic acid linoleic acid

Example of a synthetic penetration enhancer?

Laurocapram Azone

Ideal properties of penetration enhancers?

Non-toxic chemically inert reversible and selective

Why is CPE selection challenging?

Chemically diverse concentration-dependent mechanisms poorly understood

Which CPEs suit hydrophilic drugs?

Polar penetration enhancers

Which CPEs suit lipophilic drugs?

Non-polar penetration enhancers

What are amphiphilic penetration enhancers?

Compounds with polar head and non-polar hydrocarbon tail

Why are cis-unsaturated fatty acids more potent CPEs?

They disrupt stratum corneum lipid packing more effectively

Example of a potent cis-unsaturated CPE?

Oleic acid