Saturday, November 1, 2014

What is a cream? what is ointment ? what is lotion ?

What is a cream?
A cream is a semi-solid mixture of water and lipids. Creams usually look opaque white (like fresh cream). Water and lipids do not blend, but can form an ‘emulsion’ in which small droplets of one
are suspended in the other: either droplets of lipids in water or droplets of water in lipids. If the cream is ‘lipids in water’ (e.g. aqueous cream), it will evaporate and so is cooling, and the cream
will mix with water so it can be washed off. If the cream is ‘water in lipids’ (e.g. oily cream), it is more difficult to wash off. Because creams contain water, they can spread easily over moist areas of
diseased skin whereas ointments slip off.


What is in a cream?
• Active drug
• Base (the mixture of water and lipids)
• Emulsifying agents (which help to stabilise the emulsion)
• Antibacterials
• Perfumes (sometimes)
There may be a risk of developing allergic contact dermatitis to these different components, even though the active drug is not allergenic.

What is an ointment?
Ointments are semi-solid mixtures of lipids (no water). They feel greasy and look transparent and grey. Drugs such as corticosteroids may be added to both cream and ointment bases.

Ointments stick well to dry diseased skin.
‘If it’s dry, use an ointment, if it’s wet, use a cream.’

What is a lotion?
A lotion is a liquid, usually water or sometimes alcohol, containing a medication. The liquid evaporates, leaving the medication spread over the surface.

What is an emollient?
An emollient (or ‘moisturiser’) is something that moisturises and softens the skin surface. Both creams and ointments can be emollients.


How often should drugs be applied?

The pharmaco-kinetics of many commonly used topical drugs are not well worked out. Traditionally, topical drugs have been used 2–3 times per day, often with no real evidence. There may sometimes
be a patient-perceived benefit from the emollient action of some drugs, encouraging more frequent use than is pharmacologically necessary. Probably potent topical steroids would be equally
effective used only once daily. Adherence is greater for once daily than for twice daily.

Topical steroids
Topical steroids revolutionised treatment of inflammatory skin
disease in the 1950s. They are still the first choice for most inflammatory skin conditions.
The myths: ‘Topical steroids are dangerous.’ ‘They should only ever be used very sparingly.’
The facts: Topical steroids have a range of potencies (strengths):

• Mild potency: minimal risk of side-effects. Least effective. e.g. hydrocortisone 0.5%, 1.0%, 2.5%.
• Moderate potency: minimal risk of side-effects. Mildly effective. e.g. clobetasone butyrate (Eumovate®).
• Strong potency: side-effects only if used daily for >2–3 weeks. Safe to use for few days in acute situations. Very effective. e.g. betamethasone valerate (Betnovate®).

• Very strong potency: high risk of side-effects. Extremely effective. e.g. clobetasol propionate (Dermovate®). Needed for resistant conditions (e.g. discoid lupus erythematosus), poor absorption
sites (e.g. palms).

Side effects of potent topical steroids if used widely in the long term
Skin:
• Thinning of dermis: ‘atrophy’
• Telangiectasia
• Rosacea, acne, peri-oral dermatitis
• Hirsutism
• Fragility of skin, easy bruising and tearing
• Contact allergy
Systemic absorption (inflamed skin absorbs drugs more easily):
• Cushing’s syndrome.

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