Semi solids

Question 1

What are the local uses?

Answer 1

Inflammation, pain, itching, protection, lubricant, emollient

Question 2

What are the types of semi solids?

Answer 2

Ointments, creams, pastes, gels

Question 3

What is the systemic action?

Answer 3

Percutol ointment (vasodilator)

Question 4

What are the features of ointments?

Answer 4

• They are greasy
• have an oily (usually anhydrous) vehicle
• may contain a surfactant if used as a wash
• they are highly occlusive and so good for dry skin

Question 5

What are the features of creams?

Answer 5

• they are semi solid emulsions
• they have a cooling effect on the skin
• less greasy and less occlusive than ointments
• they are hydrous so require preservatives

Question 6

What are the features of pastes?

Answer 6

• stiff preparations so less spreadable
• they are ointments with up to 50% water
• they provide precise localised treatment
• forms a thick, impermeable layer on the skin
• they are used for lesions, sun block, rashes

Question 7

What are the features of gels?

Answer 7

• they have two components, a polymer to produce a matrix, and a high water content
• they are used for lubrication or for mouth ulcers

Question 8

What are the types of excipients needed in semi solids?.

Answer 8

oily/water miscible vehicles, gelling agents, surfactants, humectants, solids, preservatives, anti-oxidants

Question 9

What are the different types of oily vehicles used?

Answer 9

• mineral oils such as liquid paraffin (these are occlusive but have limited penetration)
• Vegetable oils such as caster/olive/coconut (these can turn rancid)
• synthetic oils such as dimethacone (water repellent and occlusive)

Question 10

What surfactant would be used for a w/o emulsion?

Answer 10

lanolin or bees wax

Question 11

What do antioxidants do?

Answer 11

they prevent decomposition

Question 12

In what ways can the stability of semi solids be affected?

Answer 12

They are affected by heat, light and microbial growth. Emulsions can crack
Oils can turn rancid
The higher the water content, the less stable

Question 13

How can semi solids be packaged?

Answer 13

glass/plastic jars, aluminium/plastic tubes, pump dispensers, nozzles, sachets

Question 14

What are the advantages of ointments and pastes?

Answer 14

• more stable than creams and gels
• occlusive and protective
• good for dry skin
• less need for preservatives
• some ointments can be used as washes

Question 15

What are the disadvantages of ointments and pastes?

Answer 15

• they’re greasy and sticky
• slow skin absorption
• can’t be used on macerated skin
• high oil content can be flammable

Question 16

What are the advantages of creams and gels?

Answer 16

• non greasy and more acceptable to patients
• rapid skin absorption
• have a cooling effect on evaporation
• can be used on macerated skin
• gels have less additives

Question 17

What are the disadvantages of creams and gels?

Answer 17

• susceptible to microbial contamination
• require preservatives
• less stable and creams can crack (have a short expiry)
• short duration of action due to rapid absorption

Question 18

Discuss aerosols for topical application

Answer 18

• They can be in solution or suspension formulated as liquid or foam
• They require a propellant such as CFC’s or HFA’s
• They’re packaged in metal canisters which can’t be stored above 50 degrees (chance of explosion)
• You have to shake the aerosol to disperse the propellant and drug