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Classification of ointment base

Two ways of classifying

1) composition of base
- oleaginous base
- absorption base
- emulsion base
- water soluble base.

2) degree of penetration of ointment upon application to skin
- Epidermatic Little power of penetration E.g. oleaginous bases (Hydrocarbon)
- Endodermatic Some power of penetration E.g. oleaginous base (Vegetable oil), absorption bases
- Diadermatic Deep penetration promoting systemic drug absorption E.g. emulsion bases, PEG bases


What is an oleaginous bases

Composed of entirely lipophilic materials

may consist of more than one such substances.

eg petrolatum, paraffin wax, liquid paraffin, microcrystalline wax, ceresin, plastibase
Vegetable oils
eg peanut oil, almond oil, sesame oil, olive oil, coconut oil,
Hydrogenated and sulfated oils
eg hydrogenated cotton seed, soya bean, corn and castor oils
Fatty Acids, alcohols and esters
eg stearic acid, oleic acid, palmitic acid, myristic acid, lauric acid, stearyl alcohol, cetyl alcohol, oleyl alcohol, lauryl alcohol, myristyl alcohol, glyceryl tristearate, isopropyl myristate, ethylene glycol dilaurate/distearate
eg dimethylpolysiloxanes methylphenylpolysiloxanes stearyl esters of dimethylpolysiloxanes


What is petrolatum

A type of Hydrocarbon (oleaginous base)

Tasteless,odourless,greasy Melting point:38-60C Excellent emollient Compatible with many drugs
Provides optimal drug stability


Properties of oleaginous base

- Anhydrous
-non hydrophilic
-non-water removable


Advantage of using oleaginous base

1) it can be used to incorporate active ingredients that are prone to hydrolysis.

2) it can be used to hold volatile ingredients (cannot use hydrophilic base)
eg tiger balm

3) Ideal formulation for eyes, piles (hemorrhoid; at rectal)
coz wont be wash off easily by water.

4) Prevent lost of water from skin by forming a layer.

5) good for dry skin and prevent dry skin.


Disadvantage of oleaginous bases

Hard to wash off with water--> use soap

not for hairy places like hair.


What is absorption base

A type of ointment base
which has the ability of absorbing considerable quantities of water (30%) and still retaining their ointment-like consistency (consistency wont decrease)

They do not contain water as a component in their basic formula. Generally composed of oleaginous base incorporated with hydrophilic substance(s), such as cholesterol, wool fat, lanolin alcohols and surfactants.

Hydrophilic substances gives the ability for AB to absorb water.


Absorption bases provide _____

provide some occlusion of the skin, hydrate the strateum corneum and can be left in contact with the tissue for prolonged periods of time.


Wool fat is???

A type of absorption base.

Anhydrous lanolin Complex mixture including cholesterol, lanolin alcohols and lanolin esters A natural absorption base Problem with allergy


Break down the formulation

Simple Ointment BP
Wool fat 50g
Hard paraffin 50g Cetostearyl alcohol 50g White/Yellow soft paraffin 850g

wool fat
- Absorption base
making this formulation more hydrophilic

the rest are oleaginous bases.

Hard paraffin and cetostearyl alcohol are waxy material that helps to increase consistency ,


break down Hydrophilic Petrolatum USP

Cholesterol 3%
Stearyl alcohol 3%
White wax 8%
White petrolatum 86%

Cholesterol is absorption base

stearyl alcohol and wax are to increase consistency


Properties of absorption bases

absorb water
insoluble in water

- open container can absorb water
- not good for Abx that is prone to hydrolysis

Occlusive therefore good emollient.

suitable for incorporation of hydrophilic (aq) solution of drug


What is emulsion base

These are semi-solid emulsions or creams

Composed of one liquid dispersed in another immiscible liquid with the aid of emulgent(s)

water-in-oil emulsion bases
oil-in-water emulsion bases

Small amounts of water can be incorporated into the base without decreasing the consistency of the base markedly


Emulsion bases solid or liquid etc

liquid at higher temp
when cooled = semi-solid


Types of emulsion bases

vanishing cream and cold cream


What is vanishing cream

form from emulsion base

1)Large proportion of water (as high as 80%)

2)Stearic acid(~20%)
in situ soap, pearlescence

3) Humectant e.g. glycerin,
propylene glycol

Vanishing creams get absorbed easily and applied easily on skin

due to the presence of large amount of water it can form O/W emulsion too. thus when bottle is opened, water can be evaporated and water content inside will decrease, thus making spreading on skin difficult.
Thus humectant is needed to absorb water to prevent excess water loss


Function of stearic acid

Can be found in vanishing cream

- to form in situ soap
- pearlescence

Act as emulsifying agent to stabilize the cream.
Most stearic acid are not converted to soap. these are for pearlescence to make the cream more appealing.


Break down

Stearic acid 20% Potassium hydroxide 1.4%
Glycerin 10%
Water to 100%

Stearic acid reacts with potassium to form emulsifying agent and some extras are for pearlescene

Glycerin (humectant) is to prevent excess water loss

No oil presence and stearic acid is the only lipophilic compound.


Break down
Stearic acid 15%
White wax 2%
White vaseline 8% Triethanolamine 1.5% Propylene glycol 8% Water to 100%

Stearic acid reacts with triethanolamine to give triethanolamine stearic

propylene glycol acts as humectant

presence of white vaseline makes formula more greasy.


What is cold cream

A type of emulsion base
Contain less water (W/O emulsion) Leave behind a layer of oil/fat on skin to protect the skin

More occlusive than vanishing cream


Break down
Basic formula
Beeswax 15%
Liquid paraffin 50% Borax 1%

Beeswax and borax are emulgent

beeswax cause formulation to be semi-solid


Properties of emulsion base (O/W and W/O)

O/W type
Hydrophilic (miscible) Insoluble in water Water-removable Non-greasy
Poor emollient

W/O type
Hydrophobic (immisicible)
Insoluble in water Non-Water-removable Greasy
Good emollient (2nd to OB)


What are water-soluble bases

These bases are soluble in water Examples:
- Polyethylene glycol bases
- Gels (can be taken orally)

PEG can be semi-solid or Solid (use as suppository)


What are PEG

Polyethylene glycols (PEGs) are also known as carbowaxes
General chemical formula: HOCH2(CH2OCH2)nCH2OH Non-volatile, water-soluble/miscible
Relatively inert and non-irritating to skin

Do not support mould growth

PEG <1000MW = liquid
PEG >1000MW = Solid or semi-solid


properties of PEG base

- Usually anhydrous
- Hydrophilic
- water soluble
- water removable
- non-greasy
- Lipid-free
- non-occlusive

if we add water then it can be hydrous but consistency will decrease so seldom done

NOT for drugs that are sensitive to hydrolysis

not good sites that is easily washed off

good for hairy region (wash off easily)


What is gel

Gel is water soluble base

Semi-solids consisting of a solid component enclosing and interpenetrated by a liquid component

Solid component : large organic molecules or small inorganic particles
Liquid component: water or organic solvent

Topical gels may be prepared from various types of gelling agents
Depending on the gelling agent used, the gel may be single-phase or two-phase


types of gelling agent

1) Natural gums
- tragacanth,carrageenan pectin, agar, alginic acid

2) Cellulose derivatives
- methyl cellulose (MC)
- carboxymethylcellulose (CMC)
- hydroxypropylmethyl cellulose (HPMC)
- hydroxyethyl cellulose (HEC)

3) Synthetic polymers
- carbopol

4) Clays
- Bentonite, veegum, laponite


what is single phase gels

There are no apparent boundaries between the solid and liquid components

Solid component is lyophilic and disperses readily in the dispersion medium

Generally made up of large organic molecules
E.g. natural gums, cellulose derivatives and synthetic polymers

increase [macromolecules;gelling agent ] increases viscosity and thus become semi-solid
The macromolecules exist as “strands” in the gel


Types of strand form in gel

depending on the gelling agent and dispersion medium

1) twisted matted fibres
2) partially bounded strands

1 --> form entangled network that increases viscosity

2 --> less permeable to drug due to the high crystalline region
--> sustained released of drug; drugs are released slowly


why is gel rigid

The rigidity of the gel is attributed to the intertwining network which traps and holds the dispersion medium

Single-phase gels are generally stable on standing

A change in temperature or agitation may affect the physical state of the gel
ie changed from semi-solid to liquid