Ointment and bases Part 1

Question 1

How may ointment bases be classified?

Answer 1

1) . According to composition of base
- oleaginous base
- absorption base
- emulsion base
- water-soluble base

2) . According to degree of penetration upon application to skin
- epidermatic: little power of penetration (oleaginous base)
- endodermatic: some power of penetration (oleaginous base, absorption base)
- diadermatic: deep penetration promoting systemic drug absorption (emulsion base, PEG base)

Question 2

What are oleaginous bases made of?

Answer 2

• composed entirely of lipophilic materials

- e.g. hydrocarbon, vegetable oils, hydrogenated and sulfated oils, fatty acids, alcohols and esters, silicones

Question 3

What are the properties of oleaginous bases?

Answer 3

• anhydrous
• non-hydrophilic
  (excellent ointment bases for drugs prone to hydrolysis)
• non-water-removable
  (excellent for eye or rectal ointment base)
• greasy
• occlusive
  (layer formed on skin prevents loss of water, keeping skin hydrated plus supple)

Question 4

What is an example of an oleaginous base?

Answer 4

petrolatum

Question 5

What are the properties of petrolatum?

Answer 5

• tasteless, odourless and greasy
• melting point : 38-60 degree celsius
• excellent emollient
• compatible with many drugs
• provides optimal drug stability

Question 6

What are the properties of absorption bases?

Answer 6

• can absorb considerable quantities of water, yet still retaining their ointment-like consistency
• do not contain water as a component in their basic formula (anhydrous)
• generally composed of oleaginous base incorporated with hydrophilic substances (e.g. cholesterol, wool fat, lanolin, alcohols and surfactants).
• insoluble in water
• greasy
• occlusive

Question 7

What is an example of an absorption base?

Answer 7

wool fat

Question 8

What are the properties of wool fat?

Answer 8

• anhydrous lanolin
• complex mixture including cholesterol, lanolin alcohols and lanolin esters.
• a natural absorption base
• problem with allergy

Question 9

What are the characteristics of emulsion bases?

Answer 9

• also known as creams (semi-solids)
• composed of one phase dispersed in another immiscible phase with the aid of emulgents (e.g. water-in-oil emulsion bases, oil-in-water emulsion bases).
• small amounts of water can be incorporated without significantly decreasing the consistency of the base.

Question 10

What are examples of emulsion bases?

Answer 10

A). Vanishing creams

• contain large proportion of water
• stearic acid (~20%): in situ soap, pearlescence
• humectant (e.g. glycerin, propylene glycol)

B). Cold creams

• contain much less water (water <50%, is found in the disperse phase)
• leaves behind a layer of oil/fat on skin.

Question 11

What are the properties of oil-in-water type of emulsion bases?

Answer 11

• hydrophilic
• insoluble in water
• water-removable
• non-greasy
• poor emollient
• non-occlusive

Question 12

What are the properties of water-in-oil type of emulsion bases?

Answer 12

• hydrophobic / lipophilic
• insoluble in water
• not water-removable
• greasy (continuous phase in oil)
• good emollient
• occlusive (forms a layer on the skin, good emollient)

Question 13

What are the different examples of water-soluble bases?

Answer 13

• polyethylene glycol bases (PEG)

- gels

Question 14

What are the characteristics of PEG bases?

Answer 14

• non-volatile, water-soluble/miscible
• relatively inert and non-irritating to skin
• do not support mould growth
• PEGs range from liquids to waxy solids
• Blends are used to produce base with desired consistency.

Question 15

What do gels consist of?

Answer 15

• semi-solids
• solid component enclosing and interpenetrated by a liquid component.
• solid component: large organic molecules or small inorganic molecules
• liquid component: water or organic solvent

Question 16

What are the characteristics of single-phase gels?

Answer 16

• solid component is lyophilic and disperses readily in the dispersion medium.
• generally made up of large, organic molecules (e.g. natural gums, cellulose derivatives and synthetic polymers)
• macromolecules –> increased viscosity
• macromolecules exist as “strands” in the gel, either in the form of twisted matted fibres or partially bounded strands.
• the rigidity of the gel is attributed to the intertwining network which traps and holds the dispersion medium.
• single-phase gels are generally stable on standing
• a change in temperature or agitation may affect the physical state of the gel.

Question 17

What are the characteristics of two-phase gels?

Answer 17

• solid component is lyophobic, does not disperse readily in the dispersion medium.
• generally made of small inorganic particles (e.g. clays)
• increase in particles –> little effect on consistency of the gel
• particles exist as floccules in the gel
• two-phase gels are generally less stable.

Question 18

What are the properties of gels?

Answer 18

1. Sol-gel transformation
   Induced by temperature –> thermal gels (e.g. methylcellulose, gelatin)
   Induced by shear stress –> thixotropic gels (e.g. bentonite)
2. Ability to absorb water with significant or insignificant increase in volume (swelling vs imbibition)
3. Syneresis (shrinkage of gel on storage, which causes some liquid to be squeezed out)

Question 19

What are the general indications for ointment bases?

Answer 19

• as a vehicle for drug to be applied to the skin

- as an emollient