Emulsions, Creams and Ointments

What are topical formulations and drug delivery designed to do?

Directly impact skin to improve its barrier function or deliver drug into skin

What does transdermal drug delivery focus on?

Delivering drugs through skin into systemic circulation

What’s the difference between creams and ointments?

Creams are emulsions

What is an emulsion?

liquid that don’t mix tg put in a container will have an oil and water phase

When theyre mixed tg the phase thats in greater quantity = continuous phase

Phase present in lesser amount forms spherical droplets dispersed in continuous phase

Mixtures of at least 2 immiscible/partially immiscible liquids

What is the difference between an oil-in-water and water-in-oil phase?

O-i-W: oil droplets in bulk water phase

W-i-O: water droplets in large oil phase

But, if mixing stops and the sol is left to rest, oil droplets will begin to come tg to form 1 mass and the 2 l will separate unless an additional ingredient called an emulsifier is added to stabilise spherical droplets

What cforms of application can emulsions be made for?

oral, parenteral and topical

What kinds of emulsions are O/W Vs W/O based?

Oral + IV = O/W

Dermatological = O/W + W/O

What is the difference between W/O AND O/W?

W/O = greasy, don’t mix well w aquous wound exudates (fluid released from wound, sometimes hard to wash off skin, hydrate skin by occlusion

O/W = lotions and creams readily mix w tissue exudates and are more easily removed by wash

How is the formulation of emulsions decided?

Depends on a range of factors like desired consistency

Miscibility of oil w Aq phase

Drug solubility in oil phase (if drug present)

Ingredients selected often done by trial and error

How is the type of emulsion decided?

Depends on the quantity of each phase: larger amount of certain phase will make it more likely to be continuous phase as there are more droplets present which come tg faster when a shaken container is at rest

What is the effect of an emulsifier on what liquid takes the continuous phase?

The solubility of the emulsifier will also dictate which l forms the continuous phase

E.g. if emulsifier more soluble in water phase and is less oily then water will be continuous phase to make O/W emulsion

In practice dispersed phase makes up ab 30% of emulsion

What are creams?

O/W emulsions

White semisolids that can be made with or without an active ingredient

Applied to skin or certain mucous mems for protective, therapeutic or prophylactic (intend to stop disease) reasons esp where occlusive effect no needed

Emulsions are 2-phase systems, single phase systems like ointments also available

What are ointments?

Single-phase semisolids made by combining various bases to make final desired consistency and effect on skin

What can ointment bases be classified into?

Hydrocarbon Bases

Absorption Bases

Water-miscible Bases

Water-soluble Bases

What are the function of hydrocarbon bases?

• Absorb little water from the skin

• Prevent water in the skin from escaping into the environment

• They are waterproof and occlusive

• They hydrate the skin very well and thus allow a greater amount of any drug they carry to penetrate the skin

• E.g. paraffin

What is the function of absorption bases?

• Can absorb water and secretions from skin to make a resultant W/O emulsion on skin

• Less occlusive than hydrocarbon but still have great moisturising effect

• E.g. wool fat

What is the function of water-miscible bases?

• Easier to remove from skin than hydrocarbon and abs bases

• Commercially available as epaderm and hydromol ointment

What is the function of water-soluble bases?

• Mix readily with skin secretions

• Non-occlusive

• Easily washed off skin

• Commercially available example: Bactroban Ointment

How can a drug’s properties and intended use of a cream/ointment be important for formulation?

• E.g. tracrilomus topical treatment for atopic eczema

  • Presents as dry, cracked/tichkened skin

  • Needs more occlusive treatment to hydrate and soften skin

  • Has poor water solubility so when added to more aq/watery formulation like cream drug wouldn’t mix tg and remain in its solid state

  • If added to oilier form drug would be freely available and would penetrate skin and reduce inflammation faster