Ointments and Pastes part 2 Flashcards
What are the four main types of ointment bases?
- Hydrocarbon
- Absorption
- Water miscible
- Water soluble
A) What are some of the constitutents of hydrocarbon bases?
B) What are the properties of hydocarbon bases?
A)
- Paraffins – liquid and solids – various combinations to achieve different consistencies
- Combine with other constituents to form absorption or emulsion bases.
B)
- Emollient
- Occlusive - limiting the evaporation of moisture from the skin (Pastes less so, due to presence of powders)
- Non-water washable (not readily removed from skin)
- Hydrophobic - have a low capacity to absorb water – presence of powders in pastes increases absorptivity.
What does Wn (Water number) mean?
Wn = Expresses the weight of water that can be absorbed by 100g of base at 20°C
Give three examples of a hydrocarbon base and the uses of them
1) Yellow & White Soft Paraffin BP
- Semi-solid hydrocarbons obtained from petroleum
- Soft Paraffin has a Wn of approximately 12
Uses: Alone as ointment or paste bases or as constituents of ointment or paste bases + For protection and where prolonged contact time is required
(Formulation: Dithranol ointment APF)
2) Hard Paraffin BP
* White solid
Uses: stiffening agent in Paraffin Ointment BP, Simple Ointment BP and Wool Alcohols Ointment BP
3) Liquid Paraffin BP
- Viscous liquid
- Trituration of powders to reduce particle size
(Formulation: Emulsifying ointment APF)
What are the advatages and disadvantages of parrafin bases (hydrocarbon bases)
Advantages of paraffin bases
- Stable
- Low sensitivity index
- Relatively unreactive chemically, stable and compatible with most medicaments.
- Consistency of yellow and white soft paraffin makes them suitable as bases alone
- Protective and prolong contact of medicament.
Disadvantages of parrafin bases
- Greasy
- Difficult to remove from clothing and skin
- Inability to combine with aqueous liquids except through addition of hydrophilic materials
A) What are absorption bases? What are the types of absorption bases?
B) What are their properties?
A)
- Non-aqueous formulations to which significant proportions of aqueous phase may be added (absorbed)
- Non-emulsified bases and Water in Oil (W/O) emulsions
B)
- Emollient
- Occlusive
- Absorb water - Absorption does NOT describe the mode of action of the base
- Greasy
For non-emulsified bases (absorption bases);
A) What are they, what components do they consist of
B)Provide four examples with properties/disadvantages/uses
A)
- Hydrophobic base containing a w/o emulsifier
- Can hold limited amounts of aqueous liquids and solutions of medicaments
- Not easily removed from the skin
- Components not completely hydrophobic (wool fat, wool alcohols, beeswax, cetostearyl alcohol)
B)
- Wool Fat BP: Purified, anhydrous, fat-like substance obtained from the wool of sheep
Properties: Tenacious - very sticky - rarely used alone + Insoluble in water
Disadvantages: Characteristic, slightly objectionable odour + tendency to become rancid on exposure to light, air and moisture
- Wool Alcohols BP: Obtained by treating wool fat with alkali and separating the fraction which contains mainly cholesterol and other alcohols.
Properties: Golden brown solid, characteristic odour + Adding 5% wool alcohols to soft parrafin –> 3% increase in Wn
- Beeswax BP
Properties: Melting point 62-65ºC (high) + Insoluble in water
Uses: Stiffening agent in ointment formulations
- Cetostearyl Alcohol BP: Mixture of solid aliphatic alcohols
Properties: Melts to a clear, colourless or pale yellow liquid + insoluble in water + advantage over wool fat (colourless, lower sensitibity index), increases the Wn of hydrocarbon bases
For Water/OIl (W/O) emulsion bases (absorption bases);
A) Explain what is and how it works
B) Give an example
A)
- Oily external phase
- Can absorb water but immiscible with an excess of water
B)
- Oily Cream BP, Lanolin (Wool fat hydrous – 30% water)
For water miscible bases;
A) How are they formed?
B) Give some examples
C) Properties
D) Uses
A)
- Mix with water, by forming o/w emulsions, and are easily removed from the skin and clothing
B)
- Emulsifying Ointment BP (also APF) –> contains liquid paraffin, white soft paraffin, and some wax
C)
- High patient acceptability
- Not occlusive
- Suitable for application to scalp and hair
- Miscible with exudates from lesions
- Good skin contact
- Form O/W emulsions with water
D)
- Base for topical medicaments eg Benzoic Acid Ointment Compound APF
- Preparation of o/w creams
For Water Soluble Bases;
A) How are they formed
B) Properties
C) Constituents
D) explain the property of this constituent
A)
- Bases that completely dissolve in water. Most are a blend of ingredients, many contain Polyethylene Glycols (Macrogols)
B)
- Usually anhydrous
- Non greasy
- Non occulsive
- Lipid free
- Water soluble and washable
C)
- Macrogols = Polethylene Glycols (PEG)
- They are identified by their approximate molecular weights
> 200-600 are viscous, colourless, hygroscopic liquids
>1000 and above are wax-like solids
- Consistency of base varied by adjusting the balance of liquid and solid macrogols
D)
Properties of Macrogols
- Non toxic, non-irritating
- Well absorbed by skin
- Do not hydrolyse, deteriorate or become rancid or support the growth of mould
- Remain soft on application
- Compatible with many medicaments
Summarise the 4 main types of ointment bases and their properties
What are 5 general ointment ingredients?
- Vegetable Oils eg Olive oil, castor oil – softening agent, emollient
- Silicones – synthetic water-repellent polymers –> barrier
- Organic Esters – stable substitutes for vegetable oils eg isopropyl myristate - emollient
- Preservatives – limited use: not required in anhydrous preparations
- Antioxidants - to prevent oxidation (rancidity) of fixed oils eg BHA; to protect active ingredient from oxidation eg Na metabisulfite
What are some therapeutic ingredients found in ointments?
- Emollients – smooth stratum corneum, reduce moisture loss eg fixed oils, isopropyl myristate
- Humectants – attract and retain transepidermal water at SC eg glycerol
- Anti-pruritics – relieve itching eg menthol
- Keratolytics – reduce thickness of SC eg salicylic acid
- Rubefacients & Counter-irritants – produce warming sensation by vasodilation, and reduce pain eg capsaicin
- Anti-proliferatives - Reduce the thickness of the epithelium eg Coal Tar
- Protectants – protect exposed or damaged skin eg ZnO
- Local Anaesthetics – local pain relief eg lignocaine HCl
- Corticosteroids – suppress inflammation eg hydrocortisone
- Anti-infectives – kill microorganisms eg mupirocin
How to prepare oinments?
Fusion: method used to prepare bases. Melt ingredients with 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
What is the method of preparation?
Incorporation: Powdered or liquid medicaments can be added by trituration with a spatula on a slab (usual) or use of a mortar and pestle
> Goal is to produce an even dispersion of medicament that is free from grittiness
Step 1= particle size reduction
Step 2 = method of doubling
