Pharmaceutical Ointments and Pastes Quiz

Study Notes

Ointments are greasy or oily semisolid systems applied topically to skin and mucous membranes (e.g., rectum, vagina, eye).
Medicated ointments treat infections and inflammation.
Non-medicated ointments are used for their emollient/lubricating properties.

Pastes are semisolid dosage forms containing a high proportion of solid components.
They are thicker and stiffer than ointments.
Pastes can be made from fatty bases (e.g., petrolatum, hydrophilic petrolatum) or aqueous gels (e.g., celluloses).
They may contain one or more drugs for topical application.
Pastes are well absorbed and easily removed from the skin.
Some pastes contain hydrophobic components that prevent dehydration.
Examples include toothpaste and zinc oxide paste.
Toothpaste contains an abrasive solid for cleansing and sometimes a fluoride salt.

The choice of ointment base depends on factors such as application site, drug release rate, stability and the therapeutic agent's effect on formulation viscosity.
There are four main types of bases:
- Hydrocarbon (oleaginous) bases
- Absorption bases
- Water-miscible/removable bases
- Water-soluble bases

They are non-aqueous paraffin-based formulations.
They are emollient, restricting water loss due to an occlusive film.
They provide excellent skin retention.
Predominantly hydrophobic, making them difficult to remove with washing.
Low water concentration (<5%) can be incorporated.
Chemically inert.
Provide optimum stability for drugs like antibiotics.
Components often include hard paraffin, white/yellow soft paraffin, liquid paraffin, and microcrystalline wax.

These can contain significant amounts of aqueous phase (water in oil emulsion), unlike hydrocarbon bases.
Non-emulsified bases or water-in-oil emulsions may be used to incorporate the aqueous phase.
While containing more aqueous phase than hydrophobic bases, they remain difficult to remove with washing due to their hydrophobic nature.

These anhydrous bases contain emulsifying agents (oil in water), making them miscible with water and washable.
These bases offer several advantages like containing large volumes of water, not being occlusive, and being easily washably from skin/clothing and hair.
Examples include emulsifying ointment, cetrimide emulsifying ointment, and cetomacrogol emulsifying ointment, each of which contains varying amounts of liquid paraffin, white soft paraffin, and emulsifying wax.

These bases are entirely composed of water-soluble ingredients.
They are non-greasy, and easily removed by washing.
Are miscible with exudates from inflamed sites.
Typically compatible with most therapeutic agents.
Primarily prepared using mixtures of polyethylene glycol with different molecular weights.
Lower average molecular weights are liquid, higher weights are waxy solids.

Additional/alternative solvents (like silicone, vegetable oils, organic esters).
Preservatives
Antioxidants (lipophilic and hydrophilic)

Selection is influenced by factors like desired release rate, occlusion need, stability (short-term and long-term).
The effect of the drug's consistency on the ointment base is considered.
Patient factors like dry or weeping skin are also important.