Ointments

Question 1

What are ointments?

Answer 1

Ointments are semisolid preparations that incorporate a lipid or hydrophobic excipient and are intended for external application to the skin or other mucosal membranes.

An ointment may contain <20% water and other volatile ingredients, such as ethanol, and >50% hydrocarbons, waxes, or oils.

Question 2

Mention 3 uses of ointments.

Answer 2

i. As emollients to soften the skin and soothe it from dryness and irritation
ii. As protective barriers to prevent harmful substances from coming in contact with the skin, and
iii. As vehicles for hydrophobic drugs.

Question 3

What are the types of ointment base?

Answer 3

1. Hydrocarbon bases e.g., petrolatum, wax
2. Absorption bases e.g., hydrophilic petrolatum, anhydrous lanolin
3. Emulsion or water-removable bases e.g.hydophylic ointment, vanishing cream
4. Water-soluble bases e.g PEG 400 + PEG 4000 (40:60), propylene glycol + ethanol with 2% w/w PHC

Question 4

What are the characteristics of the different types of ointment base

Answer 4

Hydrocarbon
i. Water insoluble
ii. Not water washable
iii. Forms occlusive film on skin
iv. Anhydrous

Absorption
i. w/o emulsions or oleaginous
ii. allows incorporation of aqueous solution to form w/o emulsions
iii. Not easily water washable

Emulsion
i. o/w emulsions
ii. Leaves a hydrophobic film on skin surface when water evaporates

Water-soluble
i. Hydrophilic polymer

Question 5

Highlight the typical composition of absorption (hydrophilic) ointment base

Answer 5

1. White petrolatum (oil base of o/w) 25%
2. Stearyl alcohol (oil soluble, emollient, emulsifier and thickener) 25%
3. Propylene glycol (used in aqueous phase to increase viscosity) 12%
4. Sodium lauryl sulphate (surfactant/emulsifier) 1%
5. Water (aqueous base of o/w) 37%

Question 6

Highlight the typical composition of vanishing cream.

Answer 6

1. Stearyl alcohol (oil base of o/w) 14%
2. Other hydrophobic ingredients e.g., cetyl esters wax, glyceryl monostearate
3. Surfactant (emulsifier) 1%
4. Water (aqueous base of o/w)
5. Sorbitol (water-soluble component, humectant and thickener)

Question 7

Highlight the typical composition of a water-soluble base with low (<5%w/w) water incorporation capacity

Answer 7

1. PEG 400 40% (nonaqueous hydrophilic base, liquid at room temp)
2. PEG 4000 60% (nonaqueous hydrophilic base, solid at room temp)

Question 8

Highlight the typical composition of a water-soluble base with low (>5%w/w) water incorporation capacity

Answer 8

1. PEG 400 47.5% (nonaqueous hydrophilic base, liquid at room temp)
2. PEG 4000 47.5% (nonaqueous hydrophilic base, solid at room temp)
3. Cetyl alcohol 5% (hydrophobic content)

Question 9

Mention 5 factors that affect the selection of an ointment base.

Answer 9

1. The solubility characteristics of the drug
2. The desired rate of drug release. For example, hydrophilic drug incorporated in an o/w base would be released immediately, whereas incorporation in a w/o emulsion would lead to slower drug release.
3. Typical properties of various ointment bases, such as tendency for skin occlusion and water washability.
4. Intended use of the ointment, for example, a cosmetic use would require due attention to customer convenience factors such as water washability and nonstaining on the clothing. On the other hand, usage in a clinical setting, such as occlusive barrier on wounds that would be bandaged, might not require such considerations.
5. Whether the final product is intended for drug absorption by the skin (percutaneous drug absorption) or not (topical application).

Question 10

Disccuss two methods of incorporating drugs into ointment bases

Answer 10

i. Levigation: Involves grinding an insoluble drug into small particles while wet. This can be achieve by using a mortar and pestle or a spatula on an ointment slab. Levigating agents e.g., liquid petrolatum (mineral oil) or glycerine promote the wetting of powders for incorporation into bases.
Hydrophobic ointments and w/o emulsions are typically prepared by levigation process.

ii. Fusion: Involves melting components (such as paraffin, yellow wax, white wax, and high-molecular-weight PEGs) together to form a homogeneous mixture.
The hydrophobic components are melted together and added to the aqueous phase/water-soluble components containing an emulsifying agent with constant mixing until the mixture congeals.
Drug substances are in fine powered forms before being dispersed in the vehicle. Water-soluble salts of drugs are incorporated by dissolving them in a small volume of water and incorporating the aqueous solution into a compatible base.

This method is used when the base contains solids that have higher melting points, and when the components are stable at the fusion temperatures.
Hydrophilic o/w emulsions are typically prepared by the fusion process.
Drug substances are in fine powered forms before being dispersed in the vehicle.

Question 11

What are the evaluations of an ointment?

Answer 11

i. Appearance:Note the color, odor, and homogeneity of the ointment
ii. Consistency:Gently rub a small amount of the ointment between your thumb and forefinger to assess its texture
iii. Spreadability:Rate how easy or difficult it is to spread the ointment over the skin
iv. Washability:Rate whether the ointment is washable or non-washable
v. pH:Measure the pH of the ointment
vi. Hardness:Measure the hardness of the ointment
vii. Water number:Measure the water number of the ointment
viii. Viscosity:Measure the viscosity of the ointmentusing a viscometer
ix. Stability:Test the ointment’s stability at different temperatures
x. Non-irritancy:Test whether the ointment is non-irritant
Drug content