Ointments Types, Methods, Preparations Pharmaceutics Notes, PDF, Book

Ointments Definition

What are Ointments?

Ointments are preparations for external application but differ from creams in that they have greasy bases. The base is usually anhydrous and immiscible with skin secretions. Ointments usually contain a medicament or a mixture of medicaments dissolved or dispersed in the base.

According to the British Pharmacopoeia (BP):
Ointments are formulated to provide preparations that are immiscible, miscible or emulsifiable with the skin secretion. Hydrophobic ointments and water-emulsifying ointments are intended to be applied to the skin or certain mucous membranes for emollient, protective, therapeutic or prophylactic purposes
where a degree of occlusion is desired.
Hydrophilic ointments are miscible with the skin secretion and are less emollient as a consequence.

Ointment bases

Hydrocarbon bases

These bases are immiscible with water and are not absorbed by the skin. They usually consist of soft paraffin or mixtures of soft paraffin with hard paraffin or liquid paraffin. The paraffins form a greasy waterproof film on the skin. This inhibits water loss from the skin, thereby improving the hydration of the skin, which is particularly important in the treatment of dry scaly conditions

Absorption bases

Absorption bases are good emollients and are less occlusive and easier to apply than hydrocarbon bases. Absorption bases can be divided into non-emulsified bases and water-in-oil emulsions:

Non-emulsified

These bases absorb water to form water-in-oil emulsions. Generally, they consist of a hydrocarbon base combined with a water-in-oil emulsifier such as Wool Alcohols BP or Wool Fat BP.

Water-in-oil emulsions

These are similar to non emulsified bases but are capable of absorbing more water. The constituents of emulsified bases include Hydrous Wool Fat BP (lanolin) and Oily Cream BP (Hydrous Ointment BP).

Water-miscible/emulsifying bases

These are anhydrous bases that contain oil-in-water emulsifying agents, which make them miscible with
water and therefore washable and easily removed after use. The following three emulsifying ointments are used as water-miscible bases:

Emulsifying Ointment BP (anionic)
Cetrimide Emulsifying Ointment BP (cationic)
Cetomacrogol Emulsifying Ointment BPC (non-ionic)

As the bases mix readily with the aqueous secretions of the skin and therefore wash out easily, they
are particularly suitable for use on the scalp

Hydrophilic bases

These have been developed from polyethylene glycols (macrogols). They are non-occlusive, mix readily with skin secretions and are easily removed by washing (e.g. Macrogol Ointment BP). Macrogol bases are commonly used with local anaesthetics such as Lidocaine BP

General method for ointment preparation

Fusion

This involves melting together the bases over a water bath before incorporating any other ingredients. The ointment base may include a mixture of waxes, fats and oils, of which some are solid at room temperature and others are liquid:

Hard – Paraffin BP, Beeswax BP, Cetostearyl Alcohol BP
Soft – Yellow and White Soft Paraffin BP, Wool Fat BP
Liquid – Liquid Paraffin BP and vegetable oils

Incorporating powders into an ointment base

Soluble solids
Soluble solids should be added to the molten fatty bases at the lowest possible temperature and the mixture stirred until cold. Alternatively, if using a preprepared base, soluble solids may be incorporated
using the method employed for insoluble solids.
Insoluble solids
Insoluble solids should be incorporated using an ointment tile and spatula. If there is more than one powder to be added these should be mixed in a mortar using the ‘doubling-up’ method

Coarse powders A minimum quantity of molten fatty base should be placed in the centre of the tile and used to levigate the powders. A considerable shearing force should be applied to avoid a gritty product. The powder/fatty base mixture may then either be returned to the evaporating basin with the remaining fatty base and stirred until cold, or the remaining fatty base in the evaporating basin may be allowed to cool and triturated with the powder/fatty base mixture on the tile.

Fine powders may be triturated into the otherwise finished ointment on an ointment tile. Small amounts of powder should be added to an equal amount of ointment (i.e. using the ‘doubling-up’ technique). These should be well triturated to incorporate all of the ointment bases.

Incorporating liquids into an ointment base

Non-volatile, miscible liquids
Non-volatile, miscible liquids may be mixed with the molten fat in the evaporating basin. Alternatively, if a
pre-prepared base is used, then incorporate as for volatile or immiscible liquids.
Volatile or immiscible liquids
Volatile or immiscible liquids (e.g. coal tar solutions) should be triturated with the ointment on the ointment tile. A very small amount of the ointment should be placed on the tile and a ‘well’ made in the centre.

Traditionally, small quantities of liquid should be gently folded in to avoid splashing. An alternative method is to spread a small amount of the ointment on the tile and then ‘score’ it with a spatula. Then add small quantities of the liquid and fold them into the base gently.

If using coal tar or other volatile ingredients, these should not be weighed until immediately before
use and the beaker in which it has been weighed should be covered with a watch glass to prevent
evaporation

Reference:

Pharmaceutical Compounding and Dispensing, Second Edition, Pharmaceutical Press

Ointments Types, Methods, Preparations Pharmaceutics Notes, PDF, Book