Ointment
From Encyclopedia Jr, free information reference for Kids
An ointment is a viscous semisolid preparation used topically on a variety of body surfaces. These include the skin and the
Related topical preparations include
Ointments generally are inexpensive to purchase.
[edit] Ointment and Cream
Edited by Pharmacist,
Majid H. Al-Attar, B.Pharm.
Principle lecturer of Pharmacy
Technical Institute Of Kuffa/ Pharmacy Department
Majidkuffa 20:04, 16 November 2006 (UTC)Majid
Ointment is a semi soild preparation containing medical agent uniformly dispersed in a fatty base.
our earliest records of the use of various fats and oils date back to the Babylone - Assyria about 3000 - 5000 B.C.
Cream which are usually described as semi solid preparations less viscous than ointment.
Ointment and cream serving as vehicles for topical application of medicinal substances, they also used as emollient for skin and as protective of skin.
Precutaneous Absorption
The skin offers greater resistance to pentration by drug substances than do mucous membrane, the mucous membrane in the rectal absorbed 26% - 29% of the steroid, as compared to only 2% pentration through the skin. the keratin content in the mucous membrane is relatively low or may even be absent.
Drugs may be diffuse through the skin by three different routes : hair follicle region, the sweat gland ducts and intact Stratum corneum.
Factors influencing absorption through the skin
1. Partition Co-efficient of drug
substances possessing both water and lipid solubility are favorable absorbed through the skin. Some studies indicated that those substances with an ether : water partition co-efficient greater than 1 show optimal pentration of the skin.
2. Moisture and temperature in the environment of skin
Humidity and/or temperature show to have influence on the absorption of substances through the skin.
A ten fold increase in the skin pentration of acetylsalicylic acid and glucosteroids was obtained when the environment temperature raised from 10 °C to 37 °C. A similar increase in pentration was noted for these substances when they were applied to completely hydrated skin as compared to skin at environmental humidity of 50%.
3. Pathologic injury to the skin
Injury to the skin which disrupt Stratum corneum,result in increased skin permeability. increase blood vessels dilation may result in enhanced permeability of local capillaries.
4. Vehicle
Skin pentration of drug can be increased by the use of suitable vehicle, the pH of vehicle also can influence the rate of drug release.
Classification Of Bases
Ointment can classified according to type of base in to:
1. Oleaginous ointment base
Anhydrous, dose not absorb water readily, insoluble in water and not water removable.
2. Absorption ointment base
Anhydrous, absorb water, insoluble in water and not water removable.
3. Emulsion ointment base
A. Emulsion ointment base W/O
hydrous, absorb water, insoluble in water and not water removable.
B. Emulsion ointment base O/W
hydrous, absorb water, insoluble in water and water removable.
4. Water soluble ointment base
Anhydrous, absorb water, soluble in water and water removable.
1. Oleaginous ointment base
example:
Liquid paraffin
White soft paraffin
Yellow soft paraffin
Hard paraffin
Ceresin
This group represent the most inert of chemical compounds. Lipophilic vehicles, easily spread on skin , not absorbed by skin, difficult to wash off the skin and used as occlusive effect.
2. Absorption ointment base
example:
Anhydrous wool fat
Hydrophilic vehicles, usually are unhydrous bases which have the property of absorbing several times their weight of water, forming emulsion.
Easily spread on skin, absorbed by skin, less occlusive and good emollient effect.
However, absorption bases still possess the undesirable property of greasiness, but they are less difficult removable from the skin than are oleaginous bases.
3. Emulsion ointment base
example:
Emulsion ointment base W/O
Emulsion ointment base O/W
Lanolin and cold cream bases are classified as water in oil emulsion base, they are used as emollient, the aqueous phase hydrating the skin and the oil phase forming an occlusive covering which prevents water loss due to evaporation.
These bases are used also as vehicle for medicinal agents such as sulfur, zinc oxide,...etc.
Cold cream have characteristic feature that the presence of a relayively large amount of water loosely held in the water in oil mixture, the name cold cream reffered to cooling effect produced by the slow evaporation of water when these cream were applied to the skin.
Rx,Cold cream
Borax
Olive oil
White bees wax
Soft parafin
Distalled water
The inclusion of borax which reacted with fatty acids present in the bees wax to form sodium soap. the soap contributed to the stability of the cream.
Borax-Bees wax soap is used also in preparation of Rose water cream ( Hair cream )
Rx,Rose water cream
Borax
Almond oil
White bees wax
Rose oil
Rose water
In the later years, the vegetable oils were replaced by mineral oil, because of the greater stability of mineral oil. Paraffins such as soft paraffin not used for preparation of cold cream because there are not contain fatty acids in free form so not react with alkaline substances and the result is not forming emulsifying agent.
Bees wax is unhydrous base, consist of ester of higher fatty alcohol and free acids, the presence of this acids making them acting as emulsifying agent.
Wool fat (lanolin), the introduction of lanolin in 1885, is hydrous base consist of a complex mixture of alcohol and fatty acid, so it produced water in oil emulsion: wool fat contain wool alcohol, which is the chief emulsifying agent of wool fat because wool alcohol constitute from cholestrol and lanasterol.
wool alcohol is a crude mixture of sterols and triterpene alcohol prepared by treating wool fat with alkaline.
Rx,Wool alcohol ointment
Wool alcohol
Hard paraffin
Soft paraffin
Liquid paraffin
Wool fat have the ability to absorb water, this ability attribute to the free alcohols in lanolin, mixtures of the alcohol being better emulsifiers than a single alcohol. Many lanolin derivative ( ex, lantrol) developed in order to over come some disadvantages of lanolin such as ; its stickiness, poor solubility in mineral oil, water and alcohol, its inability to pentrate in to skin and its rancidity.
Rx,Simple ointment
Wool fat
Hard paraffin
Cetostearyl alcohol
Soft paraffin
Hydrophilic ointment and vanishing cream are classified as oil in water emulsion base, they are water removable and, hence, can be removed readily from skin.
Vanishing cream, here we have a comparatively small amount of soap emulsifying up to 80% of water, forming O/W emulsion ointment base.
The advantage of these preparation as carriers of medicinal agents supposedly lies in their high water content, this lead to more rapid release of the medicament from the base, there by favoring absorption by the skin and more rapid and satisfactory antiseptic action on the surface of the skin.
Rx,Vanishing cream
Triethanolamine
Stearic acid
White bees wax
White soft paraffin
Propylene glycol
Distalled water
Soap forming by the reaction between a fatty acid such as stearic acid and amine such as triethanolamine are widely used as emulsifying agent. In contrast with metallic soaps, amine soaps are less alkaline, hence, they are less likely to be irritant to injured epidermis.
Emulsions prepared with amine soaps are more stable in the presence of divalent and trivalent metal ions than are those prepared with monovalent metal soap like sodium oleate.
When vanishing cream are to be used as bases, one must keep in mind, that they are essentially soap and,therefore are incompatible with acids or acidic substances.
4. Water soluble ointment base
example;
Polyethylene glycol
complete water soluble base have been developed from the macrogels. They are good absorption by skin, high water solubility so very easily removed from the skin, and have good solvent properties.
PEGs are mixtures of high and low molecular weight of ethylene glycols which have the general formula:HOCH2(CH2OCH2)nCH2OH
* Vegetable oils *
Vegetable oils such as peanut oil, almond oil, sesame oil, olive oil and castor oil are mono-,di-,and tri-glycerides of mixtures of unsaturated and saturated fatty acids.
These oils are used in ointment chiefly to decrease the melting point or soften bases of a higher consistancy and, also as an adjunct to oleaginous bases to increase their emollient effects and decrease their drying effects.
These oils can be used as ointment bases in themselves when a high percentage of powder is incorporated in a small amount of oil, so that the resulting consistency is quit viscous. thus, Zinc oxide in castor oil is prepared occasionally.
Vegetable oils are used extensively in cosmotic preparation such as cold cream. the use of mineral in place of the vegetable oils gives a cream with enhanced spreading properties but less emolliency.
Castor oil differs from the other oils in that it contains hydroxy fatty acids and, therefore, has slightly different solubility properties. its soluble in alcohol 95%, where as the other oils are not.