Ointments and Their Bases

• Ointments are semisolid preparations intended for external application to the skin or mucous membranes.

Ointment Classification

• Unmedicated ointments are used for their physical effects as protectants, emollients, lubricants, and vehicles for medicated ointments
• Medicated ointments contain active constituents for their therapeutic effects.

Ointment Base Ideal Properties

• Non-irritating
• Easily removable
• Non-staining
• Stable
• pH independent
• Widely compatible with a variety of medicaments
• Melts or softens at body temperature
• Releases medicament easily

Ointment Base Classifications

• Fatty Oleaginous bases: oily and thick, good for dry skin
• Absorption bases: can soak up liquids and help medicine get deep into the skin
• Water removable bases: light and easy to wash off with water
• Water-soluble bases: completely water-based, dries quickly and feels light
• Fatty oleaginous bases do not contain water and are non-washable
• Prevention of water evaporation has an occlusive effect and acts as an emollient

Fatty (Oleaginous) Bases

• Also termed hydrocarbon bases
• Water-free
• Has an emollient effect on the skin
• Prevents moisture from escaping the skin
• Remains on the skin for a long time without drying out
• Difficult to wash off
• Acts as an occlusive dressing
• Water and aqueous preparations may be incorporated but only in small amounts and with difficulty
• Some powdered substances are incorporated after levigation with mineral oil

Paraffins

• Semisolid

Petrolatum (Soft Paraffin) Properties

• A purified mixture of semisolid hydrocarbons obtained from petroleum
• Melting point is between 38°C to 56°C, meaning it's solid at room temperature but melts when it gets a little warmer.
• Varies from yellow to light amber color
• Also known as yellow petrolatum and petroleum jelly
• Vaseline is a commercial product

White Petrolatum Properties

• Petrolatum that has been decolorized
• Used for the same purposes as petrolatum
• The non-water washable characteristics are useful for treating diaper rash and dry skin
• Also known as white petroleum jelly and white Vaseline

Mineral Oil (Liquid Paraffin) Properties

• A purified mixture of liquid hydrocarbons obtained from petroleum
• Used as a levigating substance to wet and incorporate solid substances, e.g., salicylic acid and zinc oxide
• Colorless, odorless, tasteless, oily liquid
• Insoluble in water and alcohol, but soluble in ether and chloroform

Hard Paraffin Properties

• A mixture of solid hydrocarbon obtained from petroleum
• Colorless, odorless, tasteless, translucent, wax-like substances
• Used to stiffen/strengthen the ointment base
• Congeals between 47°C and 65°C

Plastibase (Jelene) Properties

• Mixture of hydrocarbons in liquid form and wax; consists of mineral oil jelled with high molecular weight hydrocarbon wax
• Has a jelly-like consistency
• Maintains its consistency over a wide range of temperatures, from 15°C to 60°C
• Medications are released more rapidly than with petrolatum
• Provides a better-appearing ointment
• Compatible with most medicaments

Plastibase (Jelene) Disadvantages

• Menthol, salicylates, and camphor dissolved in plastibase produce ointments that are too soft, probably due to interaction with the high molecular wax used to gel the mineral oil
• Prescriptions using plastibase as the vehicle cannot be prepared by fusion because it is difficult to cool the resulting mixture to a smooth consistency
• Preparation of plastibase commercially is carried out with a shock cooling procedure (very rapid cooling to a low temperature)

Lard

• Similar to butter with a suitable ointment consistency
• Lard has poor water-absorbing power
• Lard is liable to oxidation (rancidity)

Vegetable Oils

• Liquid oils are used to give ointments a smooth and creamy consistency, e.g., olive oil, cottonseed oil, and almond oil.

Silicones

• Polymers of silicon with carbon, hydrogen, and oxygen
• Some common forms include silicone oil, silicone grease, silicone rubber, and silicone resin, make good ointments for protecting the skin from moisture