Dermal Formulations

Question 1

What are the properties of ointments? What are the bases?

Answer 1

semi-solid

• usually occlusive = retain moisture
• more oily than creams

may contain active ingredients for local delivery or for emollients and/or protective roles

hydrophobic
- water free, low polarity
emulsifying
- contain o/w emulsions, anhydrous

Question 2

What are pastes? What are the bases?

Answer 2

semi-solid
- up to 60% w/w dry solids

do not dissolve in aqueous or organic systems 
used to absorb exudates 
- fluid filtered from circulatory system
highly occlusive 
photo-protective
- protects from light

bases can be

• hydrocarbons
• fats
• aqueous gel bases = less commonly used

Question 3

What are creams?

Answer 3

semi-solid

• emulsions = more fluid than ointments or paste due to high water content (above 50%)
• external application

oil in water emulsions

Question 4

What are the advantages of creams?

Answer 4

rapidly absorbed
leaves mo residues
lubricating yet pleasant feel

easily dispersed from containers

have greatest patient acceptability/compliance

Question 5

What are the disadvantages of creams?

Answer 5

watery bases require preservatives to prevent microbial growth

may require pH buffer due to high water content

may need an anti-oxidant

formulation is more complex

Question 6

What are waxes?

Answer 6

esters of an alcohol and carboxylic acid
- both have long alkyl chains

hydrophobic malleable solids of low melting points and low viscosities when liquefied

often are blended with true waxes

Question 7

What are lotions?

Answer 7

external application to the skin

• should only be applied to intact skin
• excipients may cause damage to granulating tissues in wounds or systemic toxicity

have continuous aqueous phase
can be solutions, emulsions, suspensions

Question 8

What are gels?

Answer 8

viscous semi-solid
- contain a gelling agent

usually aqueous
- can contain polar or non-polar solvents

thickening agent provides a scaffold to provide structure to the gel

gels can dry the skin
- especially if alcohol based

gels evaporate quickly

• leaves drug in contact with the epidermis
• evaporation of solvent can cause a cooling effect

Question 9

What are powders?

Answer 9

solids

• rarely contain any potent drug substance
• may act as lubricants

adsorption is one of the most common purposes

• can adsorb sweat or other exudates
• talc, starch

highly inefficient delivery into the skin
powders are very simple, cheap, and stable medications