ointments and pastes

PHAR2001

• semi solid preparations intended for application to skin or mucous membranes

• one or more medicament, dispersed, dissolved or emulsified

• local or systemic effect

• consistency that allows for rubbing

• viscosity that allows for spreading

• can act as a solid but when force is applied can act as a liquid - plastic flow with yield value

• skin, eye, nasal, vaginal or rectal

ointments

• single phase

• solid - solid dispersions - solid substance or powdered medicament dispersed in an ointment base

• two phase - water and oil

semi solids ointments

• often occlusive - prevent moisture loss

• lubricant action

• extended duration of action

• enhanced stability for drugs prone to hydrolysis

• hydrophobic bases avoid being diluted from mucous secretions

advantages of ointments

• greasy - not patient acceptable

• difficult to remove

• staining of clothes

• high viscosity ointment

• often unsuitable for weeping sites

• poor drug release

disadvantages of ointments

• outermost layer

• absorbes alot of water

• keratinised

stratum corneum

• continuous phase - moves from high to low concentration through the skin in one phase - oily

• disperse phase - oily droplets of the water must be moved into the continuous phase - from high to low concentration

• partition - dissolved drug molecules move from the topical formulation into the stratum corneum

passage of dosage form through skin

• move through the stratum corneum cells

intracellular penetration

• move in between stratum corneum cells

intercellular penetration

• moves through sweat and sebum

shunt routes

• act on the surface and epidermis of the skin and gives local action

Epidermic ointments

• these ointments are intended to release the medicament that penetrate deeper into the skin. Partially

  absorbed.

• Simulant and local irritant

Endodermic ointments

• produce systemic effect

• nature of the drug - some water solubility, moderate lipophilicity, low molecular weight, must permeate the skin causing no irritation and sensitization to the skin

• nature of vehicle - viscosity, Drug solubility, occlusive layer; hydrate skin

• Nature of skin: thickness, Wet/hydrated or Dry skin, Density and distribution of hair follicles and sweat pores,

  pH, temperature

Diadermic ointments

• Stable

• Inert

• Non-greasy

• Non-irritating – low sensitisation index

• Non-dehydrating

• Good washability (easily removed by water)

• Compatible with all medication

• Free from objectionable odour

properties of ideal ointment base

• soft, hard and liquid paraffin

• can be combined with emulgents (substances that usually separate) to form absorption or water miscible bases.

• needs to forms an occlusive layer

• protect the skin from external factors: moisture, air, sun, chemical

• soften the skin, forming - limiting the evaporation but can cause maceration

• Hydrophobic - have a low capacity to absorb water

• greasy

• inert

hydrocarbon base

• emollient and protective properties

• Use as ointment or paste bases where prolonged contact time is required

• white is bleached to form yellow

white and yellow soft paraffin

• stiffening agent (increases melting point)

• Used as an ingredient in other types of ointment bases

hard paraffin

• Viscous liquid

• Trituration of powders to reduce particle size

liquid paraffin

• relatively unreactive chemically and compatible with most medicaments.

• Stable

• low sensitivity index

• consistency of yellow and white soft paraffin makes them suitable as bases alone.

• protective and prolong contact of medicament.

paraffin advantages

• Greasy

• Inability to combine with aqueous liquids except through addition of

hydrophilic materials.

• Difficult to remove from clothing and skin

In ointments may cause congestion by preventing evaporation or drainage

from oozing areas.

• Variable release of medicaments

paraffin disadvantages

• non-aqueous formulations to which significant proportions of aqueous phase may be added

• moderately occlusive

• Emollient - soothing

• Absorb water

• includes non-emulsified bases and water in Oil emulsions

absorption bases

• hydrophilic end and lipophilic end, facilitates the formation of links between aqueous and oily phases

• added to hydrocarbon base

emulsifying agent

• mixture of Hydrophobic base with components that has a W/O emulgent properties

• Allow incorporation of aqueous solution, resulting W/O emulsions

• Can hold limited amounts of aqueous liquids and solutions of medicaments.

• Components not completely hydrophobic, Not easily removed from the skin

• e.g wool fat wool alcohols (solid) beeswax

• tenacious - very sticky - rarely used alone.

• insoluble in water but will take up 50% of its weight of water.

Non-emulsified Bases

• Characteristic, slightly objectionable odour.

• tendency to become rancid on exposure to light, air and moisture for long periods.

• quite stable and odourless.

• may produce skin sensitivity or allergy.

Non-emulsified Bases disadvantages

• Absorbs 12x its own weight of water.

• 3x water number

Wool Alcohols

• Melting point 62-65ºC (high)

• Insoluble in water

• Stiffening agent (increases melting point) in ointment formulations

• Increases Wn – helps to form W/O emulsions/stabilizer

beeswax

• mixture of solid aliphatic alcohols

• Melts to a clear, colourless or pale-yellow liquid.

• Insoluble in water.

• Advantage over wool fat - colourless, lower sensitivity index.

• increases the Wn of hydrocarbon bases.

Cetostearyl Alcohol BP

• Oily external phase

• Can absorb water but immiscible with an excess of water

Water/Oil Emulsion base

• Mix with water, by forming o/w emulsions, and are easily removed

  from the skin and clothing.

• High patient acceptability

• Not occlusive

• Suitable for application to scalp and hair

• Miscible with exudates from lesions

• Good skin contact

• used for base for topical medicaments preparation of o/w creams

water miscible bases

• macrogols

• completely dissolve in water

• Usually anhydrous

• Water soluble and washable

• Non-greasy

• Non-occlusive

• Lipid-free

• viscous, colourless, hygroscopic liquids

• wax-like solids

water soluble bases

• Do not hydrolyse, deteriorate or become rancid or support the growth of

mould

• Non-toxic, non-irritating

• Well-absorbed by skin

• Readily washed from the skin

• Compatible with many medicaments

• Incompatible with some phenols, organic acids (eg salicylic and benzoic

acids) and Cetrimide (QAC)

macrogrol properties

• Melt ingredients over low heat and stir gently until product cools to room

temperature.

• avoid overheating as this can damage oils and waxes → yellow product

• avoid rapid or uneven cooling as high MP ingredients may solidify first →

granular product

• emulsion bases are prepared as for creams

fusion method

• trituration with a spatula on a slab (usually) or use of a mortar and pestle (rarely).

• produce an even dispersion of medicament that is free from

  grittiness.

• insoluble powders requires particle size reduction/comminution via Triturate in a mortar and pestle , Pulverization by intervention, Levigation: Small amount of ointment bases

• Levigating agent should be miscible with the ointment base

• method of doubling

• heat stable, soluble medicaments may be stirred into the molten base (Iow heat), dissolving solids in solvent/ mineral oil or finely powdered insoluble medicaments can be incorporated once the base starts to thicken

• mills have a three closely mounted ceramic rollers that the ointment is squeezed between to reduce particle size of incorporatedmedicaments.

method or preparation

• should be stored below 25oC 

• Well-sealed containers. APF recommends metal or plastic tubes. Glass or plastic jars may be used

packaging and storage

• Semi-solid preparations for application to skin or mucous membranes. Usually consist of a high

  proportion of finely powdered medicaments dispersed in a base.

• 20-50% of fine powder

• porosity allows evaporation + powders can absorb exudate even with hydrocarbon base.

• much stiffer than ointments.

• viscosity (dilatant flow) makes application difficult. Remain in place. Not suited for hairy parts.

• Applied to small areas of skin → areas of disease.

• Mostly for local effect

• prolonged contact

pastes

• Emollient

• Capable of absorbing serous exudates

• Not occlusive

• Adhere well to skin

• Provide a protective barrier

• Difficult to apply

paste properties

• surface - barrier, protective, emollient

• Stratum corneum – keratolytics

• Epidermis – antiproliferatives (eg dithranol)

• Appendages – osmotic agents

• mucous membranes – anti- inflammatories

paste site of actions

• same base type but no absorption in pastes

• High powder content (eg 60%) allows use of liquids (eg liquid paraffin)alone as bases for pastes

• Consistency of ointment bases is largely unchanged by therapeutic ingredients, so needs to be semi-solid

• Gels as bases for pastes

bases for ointments and pastes

• used due to high powder content - not occlusive

• applied thickly around a fistula or sinus to protect the surrounding skin from the discharge.

liquid paraffin paste base

• 50% powders can be prepared by ‘melt and stir’. If less than 50% powders, this method will

produce a granular product.

• Very firm product and better protective and absorptive than ointment

• Dithranol is very potent and reactive (metal, air).

soft paraffin paste base

• aids the dispersion of coal tar and facilitates its removal from skin.

• keratolytic, exfoliative, antipruritic 

emulsifying wax paste base

• Drawing agent to treat boils and carbuncles. This is due to the powerful osmotic effect of glycerol and the salt.

glycerol paste base

• adheres to mucous membranes used to treat oral conditions.

gel paste bases

• Reduce the thickness of the epithelium 

antiproliferative

• Fusion - melt base ingredients together and cool (with stirring) to room temperature (unless

base is a liquid)

• Comminute solids. Trituration of powdered ingredients (in a mortar or on slab).

• Stirring in powder into melted base if very high concentration (50%) of powders.

preparation of pastes

• Packaged in glass or plastic jars or collapsible tubes

• water or volatile ingredients should be supplied in well-closed containers .

• store below 25

packaging and storage of pastes

• not specific mandatory tests for bases

• Assay and impurities

• Single dose, systemic acting: Uniformity of dosage units

• Sterility

• Microbiological testing

• Viscosity testing

• Appropriate release of active ingredient

• Homogeneity

• Particle size analysis as appropriate

BP controls for both ointments and pastes