(8) It has permanency, good keeping qualities, and neither becoming rancid
nor supporting microbial growth.
(9) It is compatible with a wide range of medicinal substances and with
other bases with which it is likely to be mixed.
(10) It releases the incorporated medication effectively to the site of
application, and if so intended, passes into or through the skin.
(11) It is washable. Unfortunately, not all ointments, creams, and pastes
meet this requirement.
CLASSIFICATION OF OINTMENT BASES
Ointment bases can be classified according to composition and general
characteristics. The ointment base or vehicle may or may not be therapeutically active.
It may be used without active ingredients if only protection or emollient properties are
desired. Ointment bases fall into one of these classes: oleaginous, absorption,
emulsion, or water-soluble.
a. Oleaginous Ointment Bases. Oleaginous ointment bases include not only
vegetable oils and animal fats, but also hydrocarbons derived from petroleum. Because
of their nature, oils and fats become rancid and foul smelling on exposure to the
atmosphere and to light. Preservatives and antioxidants are necessary ingredients in
these bases. The hydrocarbon bases may include liquid petrolatum to lower viscosity or
white wax to raise it. White Ointment, USP is a typical combination of hydrocarbons.
(1) Petrolatum (Vaseline). Petrolatum is a tasteless, odorless,
yellowish, greasy solid with a melting point between 38 Celsius (C) and 60C. White
petrolatum is decolorized petrolatum. It is used more frequently than yellow petrolatum.
Petrolatum is very stable, very compatible with most substances, and emollient to the
skin. The consistency can easily be varied by the incorporation of mineral oil (liquid
petrolatum) or white wax. Petrolatum-type ointment bases are more stable than
vegetable- or animal-type bases. However, all of these bases are greasy. The degree
to which they release the incorporated medication is questionable. They are able to
absorb only very small amounts of water, unless treated with cholesterol.
(2) (Jelene (Plastibase). Jelene, a mixture of hydrocarbons in the liquid and
wax ranges, has a jelly-like consistency. It is better than petrolatum in many respects.
It maintains its consistency over a wide range of temperature without additives. It
releases medication more reliably and provides a better appearing ointment.
(3) Silicones. Silicones, polymers of silicon and oxygen, make good
ointments for protecting the skin from moisture.