OINTMENT

Pharmaceutical ointments (termed unguents) are semisolidsystems that are applied externally, primarily to the skin and also to mucous membranes, e.g. the rectum, the vagina/vulva, the eye.
Typically, medicated ointments are used for the treatment of infection, inflammation and pruritus. However, non-medicated ointments are commonly used due to their emollient/lubricating
properties. 

“Ointments are semisolid preparation intended for application to the skin with or without inunction. they may beoleaginous e.g., white ointment; they may be entirely free of oleaginous substances e.g., polyethylene glycol ointment, or they may be emulsions of fatty or wax like material containing relatively high proportion of water e.g., hydrophilic ointment.”

  ADVANTAGES
Handling of ointments is easier than bulky liquid dosage forms.
They are chemically more stable than liquid dosage forms.
They facilitate application of the directly to the effected body part and avoid exposure of other parts to the drug.
They are suitable for patients who find it difficult to take the drugs by parenteral and oral routes.
They prolong the contact time between the drug and effected area.
The bioavailability of drugs administered as ointments is more since it prevents passage through liver.
DISADVANTAGES
They are bulkier than solid dosage forms.
When applications of an exact quantity of ointment to the affected area is required, it is difficult to ascertain the same.
They are less stable than solid dosage forms.

• The various types of ointments are

Medicated ointments
Unmedicated ointments

MEDICATED OINTMENTS
These ointments contain drugs which show local or systemic effects. These are of several sub-types
Dermatologic ointments
Opthalmic ointments
Rectal ointments
Vaginal ointments
Nasal ointments
DERMATOLOGIC OINTMENTS
These ointments are applied topically on the external skin. The ointment is applied to the affected area as a thin layer and spread evenly using gentle pressure with the fingertips.These are of three types
(1) Epidermic ointments: The drugs present in these type of ointments exert their action on the epidermis of the skin.
Example: Ketoconazole ointment.
(2) Endodermic ointments: The drugs present in these types of ointments exert their action on the deeper layers of cutaneous tissue.
Example: Demodex ointment.
(3) Diadermic ointments: The drugs present in these types of ointments enter into the deeper layers of skin and finally in the systemic circulation and exert systemic effects.
Example: Nitroglycerine ointment.
OPTHALMIC OINTMENTS
These are sterile preparations which are applied inside the lower eye lid. Only anhydrous bases are used in their preparation. The ointment is applied as a narrow band of approximately 0.25 - 0.5 inch.
Example: Sulfacetamide sodium ointment.
RECTAL OINTMENTS
These are the ointments to be applied to the perianal or within the anal canal. The bases used are combinations of PEG 300 and PEG 3350, cetyl alcohol and cetyl esters, wax, liquid paraffin and white paraffin.
Example: Benzocaine ointment.
VAGINAL OINTMENTS
These ointments are applied to the vulvovaginal area or inside the vagina. As vagina is more susceptible to infections, the ointment should be free from micro-organisms, moulds and yeasts.
Example: Candicidin ointment.
NASAL OINTMENTS
These are used in the topical treatment of nasal mucosa. Drugs get absorbed into the general circulation through the rich blood supply of the nasal lining.
Example: Ipratropium bromide ointment.
UNMEDICATED OINTMENTS
These ointments donot contain any drugs. They are useful as emollients, protectants or lubricants.
Example: Petroleum jelly.

CLASSIFICATION OF OINTMENT BASES

Four different classes of bases are available
Hydrocarbon or oleaginous bases
Absorbent bases
Emulsion bases
Water-soluble bases
HYDROCARBON BASES: 
These are semisolid hydrocarbons obtained from petroleum.
Examples: Hard paraffin, yellow soft paraffin, white soft petroleum and gelled oleaginous vehicle.
ABSORBENT BASES: 
These are hydrophilic mixtures of hydrocarbons and substances with polar groups. Substances like cholesterol, lanolin, lanosterol etc., may be used in the formation of absorption bases. 
Examples: Hydrophilic petrolatum, hydrous wool fat and oily cream.
EMULSION BASES:
 These are miscible with water and contain oil-in-water emulgents. They can be easily removed from the skin. They contain surfactants which serve the purpose of emulgents.
Based on the nature of surfactant present, emulsion bases are of three types.
(a) Anionic emulsion bases: contains anionic surfactants like sodium lauryl sulphate.
Examples: Hydrophilic ointment and emulsifying ointment.
(b) Cationic emulsion bases: contains cationic surfactants like cetrimide.
Example: Cetrimide emulsifying ointment.
(c) Non-ionic emulsion bases: contains nonionic surfactants like cetomacrogols.
Examples: Cetomacrogol emulsifying wax.
WATER - SOLUBLE BASES:
 They donot contain oily ingredients and are called greaseless bases. They are completely soluble in water. 
Examples: Polyethylene glycols (PEGs), polyoxyl 40 stearate, and polysorbates.

•   Preparation of Ointments

In either large or small-scale production, the manufacture of ointments generally involves either of two processes—incorporation or fusion.  The objective of both the methods is to disperse the finely divided or dissolved drug substance uniformly through out the vehicle.  The method for a particular preparation depends upon the nature of the ingredients.
The incorporation method involves the blending of an ingredient into the vehicle.  This is done using a glass slab and a pair of spatulas for small volumes or using a mortar and pestle for larger volumes.  Generally, stainless-steel spatulas should be used but if the possibility of any interaction exists between the substance and the spatula blade, hard rubber spatulas must be used.
When solid ingredients are incorporated into a base it is important that the particle size be as small as possible. Solid chemicals are size reduced by levigation.  This is a process of reducing a substance to an extremely fine state of subdivision by rubbing it in a glass mortar using a pestle or on a glass slab with a metal spatula.  The ingredient can be levigated with a small volume of the base until a smooth, grit-free paste is prepared.  This is then geometrically diluted with the remainder of the base.  This procedure is useful with petrolatum or oleaginous bases.
If the compound is water soluble, it is dissolved in water and is incorporated in the base.  If the base is an anhydrous oleaginous base the liquid is first incorporated into lanolin and then blended into the oleaginous base to make the final preparation.  This blending is easily accomplished using an ointment slab and spatula to levigate the mixture until a homogenous preparation is obtained.  Compounds such as volatile oils and camphor are first dissolved in a small quantity of alcohol and then incorporated into oleaginous or emulsion bases.  However, the alcohol will evaporate and result in depositions of gritty solute on standing.  Therefore, it is usually best to evaporate the alcohol from the preparation prior to incorporation into the base.
Large volumes of ointments should be blended in mechanical mixers.  Paint-type and roller-type mills replace the hand-driven spatula or pestle to ensure a uniform consistency and homogeneity of ingredients.
The fusion method is used to incorporate ingredients with solid, hard properties such as waxes or spermaceti with soft oleaginous bases.  Frequently, all of the components are combined, melted together, and cooled with constant stirring until congealing occurs and a homogenous mixture is formed.  When heat-labile substances are incorporated, those with the highest melting point are usually heated first and then as the liquid cools the other ingredients are added at temperature a few degrees above their respective melting points.  This method prevents decomposition or volatilization of heat-labile substances.  On a small scale, the fusion process can be conducted in porcelain dishes or glass beakers; on a large scale it is commonly carried out in large steam-jacketted kettles.  Once congealed, the ointment may be further levigated on an ointment slab or if a large volume is being prepared, a commercial mill can be used.