Ointment and Pastes Part 3

Question 1

A) What are pastes?

B) How are they different from ointments?

C) List some of the properties of pastes

Answer 1

A)

Semi-solid preparations for application to skin or mucous membranes. Usually consist of a high proportion of finely powdered medicaments dispersed in a base.

B)

• Pastes are ointments which contain a much higher proportion (20-50%) of fine powders
• Higher powder content –> allows evaporation + powders can absorb exudate when with hydrocarbon base
• Stiff consistency – much stiffer than ointments. Viscosity (dilatant flow) makes application difficult

C)

• Applied to small areas of skin –> areas of disease.
• Mostly for local effect
• Intended for prolonged contact
• Adhere well to skin –> protect and soothe inflamed surfaces
• Emollient + provides a protective barrier
• Difficult to apply and cosmetically unappealing
• Cant use on scalp

Question 2

What are the target areas/ regions for pastes?

Answer 2

• Skin Surface: eg Nappy Mate Paste® - protection of nappy area
• Mucuous membrane: Kenalog in Orabase® - treatment of mouth ulcers
• Epidermis: Dithranol Paste APF – psoriasis; Upton’s Paste APF - warts
• Deeper layers of skin/Appendages: Magnesium Sulphate Paste APF13 = Magnoplasm® - drawing out boils (osmotic effect)

Question 3

A) Compare the bases used in pastes and ointments (attached image)

B) Are the same bases used for ointments and pastes

Answer 3

A) see attached

B)

• Same types of bases used for both, but absorption bases not used in pastes
• High powder content (eg 60%) allows use of liquids (eg liquid paraffin) alone as bases for pastes
• Gels may be used as bases for pastes

Ointment bases –> semi-solid

Question 4

Disucss the use of hydrocarbon bases in pastes? Give some examples

Answer 4

1. Liquid paraffin
   * Liquid bases can be used due to the high content of powders.

Eg Compound Aluminium Paste BP (Baltimore Paste)

> Applied thickly around a fistula or sinus to protect the surrounding skin from the discharge

> Presence of high proportion of powders –> not occlusive

2. Soft Paraffin

Examples

• Compound Zinc Paste BP (zinc Paste) –> Astringent and Protective
• Zinc and Salicylic Acid Paste BP (keratolytic in treatment of eczema and psoraisis)
• Coal Tar Paste BP (treatment of ecezema and psoriasis)
• Dithranol Paste APF and BP (treatment of psoriasis)

Question 5

For water miscible bases used in pastes, provide some examples and their uses

Answer 5

1. Emulsifying Wax

• Emulsifying wax combined with YSP –> Emulsifying wax aids the disperion of coal tar and facilitates its removal from skin
• Emulsifying Wax in Emulsifying Ointment –> Keratolytic, exfoliative, antipruritic - may be used in the treatment of acne and seborrhoea dermatitis

2. Glycerol

• Magnesium Sulphate Paste BPC​ –> Drawing agent to treat boils and carbuncles. This is due to the powerful osmotic effect of glycerol and the salt.
• Trichloracetic Acid Paste APF​ –> TCA very caustic, caustic agent for the treatment of warts

Question 6

For water soluble used in pastes, provide some examples and their uses

Answer 6

1) Macrogols
* Unofficial dental paste formulations
2) Gel bases

• Gelatin ( Sodium Carboxymethylcellulose/pectin/gelatin in Plastibase (Orabase®) - water soluble base that adheres to mucous membranes used to treat oral conditions
• Eg Kenalog in Orabase® - contains Triamcinolone – treatment of mouth ulcers

Question 7

Decscribe what the therapeutic ingredients below do

A) Protectants

B) Keratolytics

C) Corticosteroids

D) Drawing Agents

E) Antiproliferative

Answer 7

A)

• Protect skin from harmful stimuli eg Zinc Oxide

B)

• Agents that reduce the thickness of the stratum corneum by loosening keratin eg Salicylic Acid

C)

• Agents that suppress inflammation eg Triamcinolone

D)

• Create osmotic effect to draw moisture from deeper levels of skin eg Magnesium Sulfate, Glycerol

E)

• Reduce the thickness of the epithelium eg Coal Tar

Question 8

A) How are pastes prepared?

B) How are they packaged and stored?

Answer 8

A)

• Fusion - melt base ingredients together and cool (with stirring) to room temperature (unless base is a liquid)
• Trituration of powdered ingredients (in a mortar or on slab)
• Stirring into melted base if very high concentration (50%) of powders

B)

• Packaged in glass or plastic jars or collapsible tubes
• Pastes containing water or volatile ingredients should be supplied in wellclosed containers
• BP/APF specifies storage below 25ºC